TY - JOUR A1 - Bill, Andreas A1 - Hizhnyakov, Vladimir A1 - Nevedrov, D. A1 - Seibold, Götz A1 - Sigmund, Ernst T1 - Electronic inhomogeneities, electron-lattice and pairinginteractions in high-Tc superconductors Y1 - 1997 ER - TY - GEN A1 - Seibold, Götz A1 - Castellani, Claudio A1 - Di Castro, Carlo A1 - Grilli, Marco T1 - Striped phases in the two-dimensional Hubbard model with long-rangeCoulomb interaction Y1 - 1998 ER - TY - JOUR A1 - Seibold, Götz A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir T1 - Unrestricted slave-boson mean-field approximation for the two-dimensional Hubbard model JF - Physical review Y1 - 1998 SN - 0556-2805 VL - 57 IS - 12 SP - 6937 EP - 6942 ER - TY - JOUR A1 - Feinberg, D. A1 - Germain, P. A1 - Grilli, Marco A1 - Seibold, Götz T1 - Joint superexchange - Jahn-Teller mechanism for A-typeantiferromagnetism in LaMnO3 Y1 - 1998 ER - TY - GEN A1 - Seibold, Götz T1 - Vortex, skyrmion and elliptical domain wall textures in thetwo-dimensional Hubbard model T2 - Physical review B Y1 - 1998 SN - 1550-235X VL - 58 IS - 23 SP - 15520 EP - 15527 ER - TY - JOUR A1 - Seibold, Götz A1 - Varlamov, Sergej T1 - Relationship between incommensurability and superconductivity in Peierls distorted charge-density-wave systems JF - Physical review : B Y1 - 1999 SN - 0556-2805 VL - 60 SP - 13056 ER - TY - GEN A1 - Seibold, Götz A1 - Castellani, Claudio A1 - Di Castro, Carlo A1 - Grilli, Marco T1 - Fermi surface and photoemission lineshape of incommensurate CDW systems Y1 - 2000 ER - TY - JOUR A1 - Ruckh, R. A1 - Seibold, Götz A1 - Sigmund, Ernst T1 - Influence of quantum fluctuations on solitary-wave acoustic polaron motion Y1 - 1993 ER - TY - JOUR A1 - Seibold, Götz A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir T1 - Spin-cluster states in CuO2 planes JF - Physical review B Y1 - 1993 SN - 0556-2805 VL - 48 IS - 10 SP - 7537 EP - 7544 ER - TY - JOUR A1 - Seibold, Götz A1 - Sigmund, Ernst T1 - Metal-insulator transition in doped bismuthate superconductors Y1 - 1993 ER - TY - JOUR A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir A1 - Seibold, Götz T1 - Phase-Separation in High-Tc Superconductors JF - Physica C : Superconductivity Y1 - 1994 SN - 0921-4534 VL - Vol. 235–240 IS - 1 SP - 253 EP - 256 ER - TY - JOUR A1 - Letz, M. A1 - Seibold, Götz A1 - Sigmund, Ernst T1 - Percolative Phase-Separation-Mean Field Calculations of Spin-Polarized States in CuO2 Planes Y1 - 1994 ER - TY - JOUR A1 - Seibold, Götz A1 - Letz, M. A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir T1 - Mean-Field Theories of Spin-Cluster States in copper oxide planes Y1 - 1994 ER - TY - JOUR A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir A1 - Seibold, Götz T1 - Electronic Phase Separation in High-Tc Superconductors Y1 - 1994 ER - TY - JOUR A1 - Sigmund, Ernst A1 - Seibold, Götz A1 - Bill, Andreas A1 - Wulf, Ulrich A1 - Isenmann, G. A1 - Essl, W. T1 - Dynamische Eigenschaften von Festkörpern und Molekularen Strukturen Y1 - 1995 ER - TY - THES A1 - Seibold, Götz T1 - Spin-polarisierte Quasiteilchen in der Hochtemperatursupraleitung Y1 - 1995 PB - Aachen : Shaker ER - TY - JOUR A1 - Seibold, Götz A1 - Sigmund, Ernst T1 - Differences between one and multiband Hubbard models Y1 - 1995 ER - TY - JOUR A1 - Seibold, Götz A1 - Varlamov, Sergej T1 - Spectral properties of incommensurate CDW scattering in cuprates Y1 - 2003 ER - TY - JOUR A1 - Lorenzana, José A1 - Seibold, Götz T1 - Metallic mean-field stripes, incommensurability and chemicalpotential in cuprates Y1 - 2002 ER - TY - JOUR A1 - Varlamov, Sergej A1 - Seibold, Götz T1 - Effective interactions in the stripe state of the two-dimensional Hubbard model Y1 - 2002 ER - TY - JOUR A1 - Varlamov, Sergej A1 - Seibold, Götz T1 - Influence of the pseudogap on the superconductivity-inducedphonon renormalization in high-Tc superconductors Y1 - 2002 ER - TY - GEN A1 - Seibold, Götz A1 - Varlamov, Sergej T1 - Effect of incommensurate charge-density wave scattering on theelectronic structure of high-Tc cuprates (I) T2 - Journal of Superconductivity Y1 - 2002 SN - 0896-1107 VL - 15 IS - 5 SP - 387 EP - 388 ER - TY - GEN A1 - Seibold, Götz A1 - Varlamov, Sergej T1 - Effect of incommensurate charge-density wave scattering on theelectronic structure of high-Tc cuprates (II) T2 - Journal of Superconductivity Y1 - 2002 SN - 0896-1107 VL - 15 IS - 6 SP - 505 EP - 506 ER - TY - JOUR A1 - Seibold, Götz T1 - Grundlagen und Anwendungen der Supraleitung JF - Unterrichtsblätter Deutsche Telekom Y1 - 2002 SN - 0949-3387 VL - 55 SP - S. 240 ER - TY - CHAP A1 - Seibold, Götz A1 - Castellani, Claudio A1 - Di Castro, Carlo A1 - Grilli, Marco ED - Bianconi, Antonio ED - Saini, Naurang L. T1 - Domain wall structures in the two-dimensional Hubbard modelwith long-range Coulomb interaction T2 - Stripes and Related Phenomena Y1 - 2000 SN - 0-306-46419-5 U6 - https://doi.org/10.1007/0-306-47100-0_18 SP - 151 EP - 157 PB - Kluwer Academic Plenum CY - New York ER - TY - GEN A1 - Seibold, Götz A1 - Castellani, Claudio A1 - Di Castro, Carlo A1 - Grilli, Marco ED - Barnes, Stewart E. T1 - Role of the long-range Coulomb interaction on the formation of striped phases in the two-dimensional Hubbard model T2 - High temperature superconductivity, Coral Gables, Florida, January 1999 Y1 - 1999 SN - 1-56396-880-0 U6 - https://doi.org/10.1063/1.59651 PB - AIP Publishing CY - Melville, New York ER - TY - CHAP A1 - Hizhnyakov, Vladimir A1 - Sigmund, Ernst A1 - Seibold, Götz T1 - Polaron Formation and Percolative Phase Separation T2 - Phase Separation in Cuprate Superconductors Y1 - 1994 SN - 3-540-57681-9 SP - 50 EP - 65 PB - Springer CY - Berlin [u.a.] ER - TY - JOUR A1 - Seibold, Götz A1 - Grilli, Marco T1 - Theory of isotope dependence of photoemission spectra ofhigh-Tc superconducting cuprates Y1 - 2005 ER - TY - JOUR A1 - Seibold, Götz A1 - Lorenzana, José T1 - Magnetic fluctuations of stripes in the high temperature cuprate superconductors Y1 - 2005 ER - TY - JOUR A1 - Seibold, Götz A1 - Lorenzana, José T1 - Stability of metallic stripes in the extended one-band Hubbard model Y1 - 2004 ER - TY - JOUR A1 - Seibold, Götz A1 - Becca, Federico A1 - Rubin, P. A1 - Lorenzana, José T1 - Time-dependent Gutzwiller theory of magnetic excitations in the Hubbard model Y1 - 2004 ER - TY - JOUR A1 - Lorenzana, José A1 - Seibold, Götz T1 - Dynamical and statical properties of stripes in cuprates Y1 - 2004 ER - TY - JOUR A1 - Varlamov, Sergej A1 - Seibold, Götz T1 - Temperature dependence of the collective mode and its influence on theband splitting in bilayer cuprates Y1 - 2003 ER - TY - JOUR A1 - Lorenzana, José A1 - Seibold, Götz T1 - Dynamics of metallic stripes in cuprates Y1 - 2003 ER - TY - JOUR A1 - Seibold, Götz A1 - Becca, Federico A1 - Lorenzana, José T1 - Inhomogeneous Gutzwiller approximation with random phase fluctuationsfor the Hubbard model Y1 - 2003 ER - TY - GEN A1 - Schmeißer, Dieter A1 - Schmidt, Stephan A1 - Seibold, Götz A1 - Cherkashinin, Gennady A1 - Jaegermann, Wolfram T1 - Localized Gap States in LiCoO2 and their Influence on the Transport Properties in Li-Ion Batteries T2 - ECS Transactions Y1 - 2010 SN - 1938-5862 VL - 25 IS - 35 SP - 37 EP - 45 ER - TY - GEN A1 - Oelsen, E. von A1 - Seibold, Götz A1 - Bünemann, Jörg T1 - The time-dependent Gutzwiller theory for multi-band Hubbard models T2 - New Journal of Physics Y1 - 2011 SN - 1367-2630 VL - 13 SP - 113031-01 EP - 113031-42 ER - TY - GEN A1 - Mondal, Mintu A1 - Kumar, Sanjeev A1 - Chand, Madhavi A1 - Kamlapure, Anand A1 - Saraswat, Garima A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Raychaudhuri, Pratap T1 - Role of the Vortex-Core Energy on the Berezinskii-Kosterlitz-Thouless Transition in Thin Films of NbN Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.107.217003 ER - TY - GEN A1 - Oelsen, E. von A1 - Seibold, Götz A1 - Bünemann, Jörg T1 - Time-Dependent Gutzwiller Theory for Multiband Hubbard Models T2 - Physical Review Letters Y1 - 2011 SN - 1079-7114 VL - 107 IS - 7 SP - 076402-01 EP - 076402-04 ER - TY - GEN A1 - Seibold, Götz A1 - Markiewicz, Richard S. A1 - Lorenzana, José T1 - Spin canting as a result of the competition between stripesand spirals in cuprates Y1 - 2011 ER - TY - GEN A1 - Markiewicz, Richard S. A1 - Lorenzana, José A1 - Seibold, Götz A1 - Bansil, Arun T1 - Competing phases on the cuprates: Charge vs spin order Y1 - 2011 ER - TY - GEN A1 - Seibold, Götz A1 - Grilli, Marco A1 - Lorenzana, José T1 - Influence of correlations on transitive electron-phonon couplings in cuprate superconductors Y1 - 2011 ER - TY - GEN A1 - Seibold, Götz A1 - Grilli, Marco A1 - Lorenzana, A. T1 - Dynamics of Electronic Inhomogeneities in Cuprates Y1 - 2011 ER - TY - JOUR A1 - Seibold, Götz A1 - Grilli, Marco T1 - Influence of incommensurate dynamic charge-density wave scatteringon the line shape of superconducting high-Tc cuprates JF - Physical Review B Y1 - 2001 SN - 1550-235X VL - 63 IS - 22 SP - 224505 ER - TY - CHAP A1 - Sigmund, Ernst A1 - Hizhnyakov, Vladimir A1 - Seibold, Götz T1 - Percolative Phase Separation and High-Tc superconductivity T2 - Proceedings of the Workshop on Phase Separation in Cuprate Semiconductors, Erice, Italy, 1992 Y1 - 1993 SN - 981-02-1274-7 SP - 46 EP - 66 PB - World Scientific CY - Singapore [u.a.] ER - TY - GEN A1 - Bazart, Cécile A1 - Bonein, Aurélie A1 - Hokamp, Sascha A1 - Seibold, Götz T1 - Bahavioural Economics and Tax Evasion: Calibrating an Agent-based Econophysics Model with Experimental Tax Compliance Data T2 - Journal of Tax Administration Y1 - 2016 UR - http://jota.website/article/view/74 VL - 2 IS - 1 SP - 126 EP - 144 ER - TY - GEN A1 - Markiewicz, Richard S. A1 - Lorenzana, José A1 - Seibold, Götz A1 - Bansil, Arun T1 - Short range smectic order driving long range nematic order: example of cuprates T2 - Scientific reports Y1 - 2016 UR - http://www.nature.com/articles/srep19678 U6 - https://doi.org/10.1038/srep19678 SN - 2045-2322 VL - 6 SP - 19678 ER - TY - GEN A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Castellani, Claudio A1 - Lorenzana, José T1 - Current Correlations in Strongly Disordered Superconductors T2 - Journal of Superconductivity and Novel Magnetism Y1 - 2016 UR - http://link.springer.com/article/10.1007%2Fs10948-015-3300-6 U6 - https://doi.org/10.1007/s10948-015-3300-6 VL - 29 IS - 3 SP - 577 EP - 580 ER - TY - GEN A1 - Tea, C. A1 - Castellani, Claudio A1 - Seibold, Götz A1 - Benfatto, Lara T1 - Nonrelativistic Dynamics of the Amplitude (Higgs) Mode in Superconductors T2 - Physical Review Letters Y1 - 2015 UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.157002 U6 - https://doi.org/http://dx.doi.org/10.1103/PhysRevLett.115.157002 SN - 1079-7114 VL - 115 SP - 157002 ER - TY - GEN A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto T1 - Intrinsic spin Hall effect in systems with striped spin-orbit coupling T2 - epl : a letters journal exploring the frontiers of physics KW - Condensed Matter Y1 - 2015 UR - http://epljournal.edpsciences.org/articles/epl/abs/2015/19/epl17411/epl17411.html U6 - https://doi.org/http://dx.doi.org/10.1209/0295-5075/112/17004 SN - 1286-4854 VL - 112 IS - 1 SP - 17004-p1 EP - 17004-p6 ER - TY - GEN A1 - Cea, Tommaso A1 - Bucheli, Daniel A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Lorenzana, José A1 - Castellani, Claudio T1 - Optical excitation of phase modes in strongly disordered superconductors T2 - Physical Review B N2 - According to the Goldstone theorem the breaking of a continuous U(1) symmetry comes along with the existence of low-energy collective modes. In the context of superconductivity these excitations are related to the phase of the superconducting (SC) order parameter and for clean systems are optically inactive; that is, single-mode excitations do not directly couple to light. Here we show that for strongly disordered superconductors phase modes acquire a dipole moment and appear as a subgap spectral feature in the optical conductivity. This finding is obtained with both a gauge-invariant random-phase approximation scheme based on a fermionic Bogoliubov–de Gennes state and a prototypical bosonic model for disordered superconductors. In the strongly disordered regime, where the system displays an effective granularity of the SC properties, the optically active dipoles are linked to the isolated SC islands, offering a new perspective for realizing microwave optical devices. Y1 - 2014 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.174506 U6 - https://doi.org/10.1103/PhysRevB.89.174506 SN - 2469-9969 VL - 89 SP - 174506 ER - TY - GEN A1 - Bucheli, Daniel A1 - Grilli, Marco A1 - Peronaci, F. A1 - Seibold, Götz A1 - Caprara, Sergio T1 - Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling T2 - Physical Review B N2 - We propose a model for the two-dimensional electron gas formed at the interface of oxide heterostructures that includes a Rashba spin-orbit coupling proportional to an electric field oriented perpendicularly to the interface. Taking into account the electron density dependence of this electric field confining the electron gas at the interface, we report the occurrence of a phase separation instability (signaled by a negative compressibility) for realistic values of the spin-orbit coupling and of the electronic band-structure parameters at zero temperature. We extend the analysis to finite temperatures and in the presence of an in-plane magnetic field, thereby obtaining two phase diagrams that exhibit a phase separation dome. By varying the gating potential, the phase separation dome may shrink and vanish at zero temperature into a quantum critical point where the charge fluctuates dynamically. Similarly, the phase separation may be spoiled by a planar magnetic field even at zero temperature leading to a line of quantum critical points. Y1 - 2014 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.195448 U6 - https://doi.org/10.1103/PhysRevB.89.195448 SN - 2469-9969 VL - 89 ER - TY - GEN A1 - Seibold, Götz A1 - Di Castro, Carlo A1 - Grilli, Marco A1 - Lorenzana, José T1 - Spin excitations of ferronematic order in underdoped cuprate superconductors T2 - Scientific reports N2 - High-temperature superconductors exhibit a characteristic hourglass-shaped spectrum of magnetic fluctuations which most likely contribute to the pairing glue in the cuprates. Recent neutron scattering experiments in strongly underdoped compounds have revealed a significant low energy anisotropy of these fluctuations which we explain by a model in which topological defects of the antiferromagnet clump to producing domain wall segments with ferronematic order. This state does not invoke global charge order but breaks C4 rotational and inversion symmetry. The incommensurability of the low doping charge-disordered state is in good agreement with experiment and interpolates smoothly with the incommensurability of the stripe phase at higher doping. Within linear spin-wave theory the dynamic structure factor is in very good agreement with inelastic neutron scattering data and can account for the observed energy dependent anisotropy. Y1 - 2014 UR - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4060504/ U6 - https://doi.org/10.1038/srep05319 SN - 2045-2322 IS - 4 SP - 5319 ER - TY - GEN A1 - Seibold, Götz A1 - Markiewicz, Richard S. A1 - Lorenzana, José T1 - Magnetic Structure of Electronic Inhomogeneities in Cuprates: Competition between Stripes and Spirals T2 - Acta Physica Polonica A N2 - It is shown that the magnetic structure of high-T c superconductors is strongly influenced by the next-nearest neighbor hopping parameter t' which distinguishes different families of cuprates. Our investigations indicate that uniform spirals get favored by a large t'=t ratio but are unstable at small doping towards stripes with spin canting. For large /t'/t/ spirals can be stabilized under certain conditions in the overdoped regime which may explain the elastic incommensurate magnetic response recently observed in iron-co-doped Bi2201 materials. Y1 - 2012 UR - https://www.researchgate.net/publication/230739012_Magnetic_Structure_of_Electron ic_Inhomogeneities_in_Cuprates_Competition_between_Stripes_and_Spirals SN - 1898-794X VL - 121 IS - 5-6 SP - 1019 EP - 1021 ER - TY - GEN A1 - Seibold, Götz A1 - Markiewicz, Richard S. A1 - Lorenzana, José T1 - Stripes with Spin Canting in the Three-Band Hubbard Model T2 - Journal of Superconductivity and Novel Magnetism N2 - In underdoped cuprates, both stripes and spiral states may account for the incommensurate spin response observed by elastic neutron scattering experiments. Here, we investigate the respective stability of both textures within the framework of the three-band Hubbard model which we treat within the unrestricted Gutzwiller approximation. Our calculations indicate that for parameter sets appropriate for lanthanum cuprates and small doping nor purely longitudinal stripes nor uniform spirals are stable but stripes with significant spin canting. Indeed at small doping uniform spirals are unstable toward nanoscale phase separation. KW - Stripes KW - Spirals KW - High-temperature superconductors Y1 - 2013 UR - http://link.springer.com/article/10.1007/s10948-012-1701-3 U6 - https://doi.org/10.1007/s10948-012-1701-3 SN - 1557-1939 SN - 1557-1947 VL - 26 IS - 1 SP - 49 EP - 52 ER - TY - GEN A1 - Lemarié, Gabriel A1 - Kamlapure, Anand A1 - Benfatto, Lara A1 - Lorenzana, José A1 - Seibold, Götz A1 - Ganguli, S. C. A1 - Raychaudhuri, Pratap A1 - Castellani, Claudio T1 - Universal scaling of the order-parameter distribution in strongly disordered superconductors T2 - Physical Review B N2 - We investigate theoretically and experimentally the statistical properties of the inhomogeneous order-parameter distribution (OPD) at the verge of the superconductor-insulator transition (SIT). We find within two prototype fermionic and bosonic models for disordered superconductors that one can identify a universal rescaling of the OPD. By performing scanning-tunneling microscopy experiments in three samples of NbN with increasing disorder we show that such a rescaling also describes the experimental data with excellent accuracy. These results can provide a breakthrough in our understanding of the SIT. Y1 - 2013 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.87.184509 U6 - https://doi.org/10.1103/PhysRevB.87.184509 SN - 2469-9977 VL - 87 IS - 18 SP - 184509 ER - TY - GEN A1 - Seibold, Götz A1 - Capati, Matteo A1 - Grilli, Marco A1 - Di Castro, Carlo A1 - Grilli, Marco A1 - Lorenzana, José T1 - Hidden ferronematic order in underdoped cuprates T2 - Physical Review B N2 - We study a model for low-doped cuprates where holes aggregate into oriented stripe segments which have a magnetic vortex and antivortex at the extremes. We argue that due to the interaction between segments a ferronematic state with macroscopic polarization is stabilized. This state can be characterized as a charge nematic which, due to the net polarization, breaks inversion symmetry and also exhibits an incommensurate spin modulation. Our calculation can reproduce the doping-dependent spin structure factor of lanthanum cuprates in excellent agreement with experiment and allows to rationalize experiments in which the incommensurability has an order-parameter-like temperature dependence. Y1 - 2013 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.87.035138 U6 - https://doi.org/10.1103/PhysRevB.87.035138 SN - 2469-9969 VL - 87 IS - 3 SP - 035138 ER - TY - GEN A1 - Seibold, Götz A1 - Pickhardt, Michael T1 - Lapse of time effects on tax evasion in an agent-based econophysics model T2 - Physica A: Statistical Mechanics and its Applications N2 - We investigate an inhomogeneous Ising model in the context of tax evasion dynamics where different types of agents are parameterized via local temperatures and magnetic fields. In particular, we analyze the impact of lapse of time effects (i.e. backauditing) and endogenously determined penalty rates on tax compliance. Both features contribute to a microfoundation of agent-based econophysics models of tax evasion. Y1 - 2013 UR - http://www.sciencedirect.com/science/article/pii/S0378437113000307 U6 - https://doi.org/10.1016/j.physa.2013.01.016 SN - 0378-4371 VL - 392 IS - 9 SP - 2079 EP - 2087 ER - TY - GEN A1 - Pickhardt, Michael A1 - Seibold, Götz T1 - Income tax evasion dynamics: Evidence from an agent-based econophysics model T2 - Journal of Economic Psychology N2 - • We extend existing econophysics models with respect to the behavioral heterogeneity of agents. • We analyze enforcement or audit efficiency. • We compare agent-based tax evasion models in the economics versus the econophysics domain. KW - Tax evasion KW - Tax compliance KW - Ising model KW - Econophysics KW - Numerical simulation Y1 - 2013 UR - http://www.sciencedirect.com/science/article/pii/S0167487013000408 U6 - https://doi.org/10.1016/j.joep.2013.01.011 SN - 0167-4870 VL - 40 SP - 147 EP - 160 ER - TY - GEN A1 - Bünemann, Jörg A1 - Capone, Michael A1 - Lorenzana, José A1 - Seibold, Götz T1 - Linear-response dynamics from the time-dependent Gutzwiller approximation T2 - New Journal of Physics N2 - Within a Lagrangian formalism, we derive the time-dependent Gutzwiller approximation for general multi-band Hubbard models. Our approach explicitly incorporates the coupling between time-dependent variational parameters and a time-dependent density matrix from which we obtain dynamical correlation functions in the linear-response regime. Our results are illustrated for the one-band model where we show that the interacting system can be mapped to an effective problem of fermionic quasiparticles coupled to 'doublon' (double occupancy) bosonic fluctuations. The latter have an energy on the scale of the on-site Hubbard repulsion U in the dilute limit but become soft at the Brinkman–Rice transition, which is shown to be related to an emerging conservation law of doublon charge and the associated gauge invariance. Coupling with the boson mode produces a structure in the charge response and we find that a similar structure appears in dynamical mean-field theory. Y1 - 2013 UR - http://iopscience.iop.org/article/10.1088/1367-2630/15/5/053050 SN - 1367-2630 VL - 15 ER - TY - GEN A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Castellani, Claudio A1 - Lorenzana, José T1 - Superfluid Density and Phase Relaxation in Superconductors with Strong Disorder T2 - Physical Review Letters N2 - We consider the attractive Hubbard model with on-site disorder as a prototype of a disordered superconductor. We solve the Bogoliubov–de Gennes equations on two-dimensional finite clusters at zero temperature and evaluate the electromagnetic response to a vector potential. We find that the standard decoupling between transverse and longitudinal response does not apply in the presence of disorder. Moreover, the superfluid density is strongly reduced by the relaxation of the phase of the order parameter already at mean-field level when disorder is large. We also find that the anharmonicity of the phase fluctuations is strongly enhanced by disorder. Beyond mean field, this provides an enhancement of quantum fluctuations inducing a zero-temperature transition to a nonsuperconducting phase of disordered preformed pairs. Finally, the connection of our findings with the glassy physics for extreme dirty superconductors is discussed. Y1 - 2012 UR - http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.108.207004 U6 - https://doi.org/10.1103/PhysRevLett.108.207004 SN - 1092-0145 VL - 108 IS - 20 SP - 207004 ER - TY - GEN A1 - Seibold, Götz A1 - Grilli, Marco A1 - Lorenzana, José T1 - Stripes in cuprate superconductors: Excitations and dynamic dichotomy T2 - Physica C: Superconductivity N2 - We present a short account of the present experimental situation of stripes in cuprates followed by a review of our present understanding of their ground state and excited state properties. Collective modes, the dynamical structure factor, and the optical conductivity of stripes are computed using the time-dependent Gutzwiller approximation applied to realistic one band and three band Hubbard models, and are found to be in excellent agreement with experiment. On the other hand, experiments like angle-resolved photoemission and scanning tunneling microscopy show the coexistence of stripes at high energies with Fermi liquid quasiparticles at low energies. We show that a phenomenological model going beyond mean-field can reconcile this dynamic dichotomy. Y1 - 2012 UR - http://www.sciencedirect.com/science/article/pii/S0921453412001864 U6 - https://doi.org/10.1016/j.physc.2012.03.072 SN - 0921-4534 VL - 481 SP - 132 EP - 145 ER - TY - GEN A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto T1 - Non-equilibrium Spin Currents in Systems with Striped Rashba Spin-Orbit Coupling T2 - Journal of Superconductivity and Novel Magnetism N2 - It is shown that non-homogeneity in the spin-orbit coupling (SOC) arising from structure inversion asymmetry gives rise to a finite intrinsic spin Hall conductivity in contrast with the corresponding case of a homogeneous SOC in the disordered two-dimensional electron gas. In particular, we examine the inhomogeneity arising from a striped modulation of the Rashba type spin-orbit coupling. A corresponding structure could be realized at oxide interfaces with periodic top gating or in semiconductor heterostructures. Y1 - 2017 UR - http://link.springer.com/article/10.1007/s10948-016-3774-x U6 - https://doi.org/10.1007/s10948-016-3774-x SN - 1557-1939 VL - 30 IS - 1 SP - 123 EP - 128 ER - TY - GEN A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Di Castro, Carlo A1 - Seibold, Götz T1 - Pseudogap and (An)isotropic Scattering in the Fluctuating Charge-Density Wave Phase of Cuprates T2 - Journal of Superconductivity and Novel Magnetism N2 - We present a general scenario for high-temperature superconducting cuprates, based on the presence of dynamical charge density waves (CDWs) and to the occurrence of a CDW quantum critical point, which occurs, e.g., at doping p ≈ 0.16 in YBa2Cu3O6 + δ (YBCO). In this framework, the pseudogap temperature T∗ is interpreted in terms of a reduction of the density of states due to incipient CDW and, at lower temperature to the possible formation of incoherent superconducting pairs. The dynamically fluctuating character of CDW accounts for the different temperatures at which the CDW onset revealed by X-ray scattering (Tons(p)), and the static three-dimensional CDW ordering appear. We also investigate the anisotropic character of the CDW-mediated scattering. We find that this is strongly anisotropic only close to the CDW quantum critical point (QCP) at low temperature and very low energy. It rapidly becomes nearly isotropic and marginal-Fermi-liquid-like away from the CDW QCP and at finite (even rather small) energies. This may reconcile the interpretation of Hall measurements in terms of anisotropic CDW scattering with recent photoemission experiments Bok, J.M., et al. Sci. Adv. 2, e1501329 (2016). KW - Charge-density waves KW - High-Tc superconducting cuprates KW - Anisotropic scattering Y1 - 2017 UR - http://link.springer.com/article/10.1007/s10948-016-3775-9 U6 - https://doi.org/10.1007/s10948-016-3775-9 SN - 1557-1939 SN - 1557-1947 VL - 30 IS - 1 SP - 25 EP - 30 ER - TY - GEN A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Castellani, Claudio A1 - Lorenzana, José T1 - Amplitude, density, and current correlations of strongly disordered superconductors T2 - Physical Review B N2 - We investigate the disorder dependence of the static density, amplitude, and current correlations within the attractive Hubbard model supplemented with onsite disorder. It is found that strong disorder favors a decoupling of density and amplitude correlations due to the formation of superconducting (SC) islands. This emergent granularity also induces an enhancement of the density correlations on the SC islands whereas amplitude fluctuations are most pronounced in the “insulating” regions. While density and amplitude correlations are short ranged at strong disorder, we show that current correlations have a long-range tail due to the formation of percolative current paths in agreement with the constant behavior expected from the analysis of one-dimensional models. Y1 - 2015 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.92.064512 U6 - https://doi.org/10.1103/PhysRevB.92.064512 SN - 2469-9969 VL - 92 IS - 6 SP - 064512 ER - TY - GEN A1 - Bovenzi, Nicolo A1 - Finocchiaro, Francesca A1 - Scopigno, Nicantro A1 - Bucheli, Daniel A1 - Caprara, Sergio A1 - Seibold, Götz A1 - Grilli, Marco T1 - Possible Mechanisms of Electronic Phase Separation in Oxide Interfaces T2 - Journal of Superconductivity and Novel Magnetism N2 - LaAlO 3/SrTiO 3 and LaTiO 3/SrTiO 3 (LXO / STO) interfaces are known to host a strongly inhomogeneous (nearly) two-dimensional electron gas (2DEG). In this work, we present three unconventional electronic mechanisms of electronic phase separation (EPS) in a 2DEG as a possible source of inhomogeneity in oxide interfaces. Common to all three mechanisms is the dependence of some (interaction) potential on the 2DEGs density. We first consider a mechanism resulting from a sizable density-dependent Rashba spin-orbit coupling. Next, we point out that an EPS may also occur in the case of a density-dependent superconducting pairing interaction. Finally, we show that the confinement of the 2DEG to the interface by a density-dependent, self-consistent electrostatic potential can by itself cause an EPS. KW - Oxide interfaces KW - Superconductivity KW - Electronic phase separation Y1 - 2015 UR - http://link.springer.com/article/10.1007/s10948-014-2903-7 U6 - https://doi.org/10.1007/s10948-014-2903-7 SN - 1557-1939 SN - 1557-1947 VL - 28 IS - 4 SP - 1273 EP - 1277 ER - TY - GEN A1 - Seibold, Götz A1 - Bucheli, Daniel A1 - Caprara, Sergio A1 - Grilli, Marco T1 - Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems T2 - EPL Europhysics Letters N2 - We investigate a two-dimensional electron model with Rashba spin-orbit interaction where the coupling constant $g=g(n)$ depends on the electronic density. It is shown that this dependence may drive the system unstable towards a long-wavelength charge density wave (CDW) where the associated second-order instability occurs in close vicinity to global phase separation. For very low electron densities the CDW instability is nesting-induced and the modulation follows the Fermi momentum kF. At higher density the instability criterion becomes independent of kF and the system may become unstable in a broad momentum range. Finally, upon filling the upper spin-orbit split band, finite momentum instabilities disappear in favor of phase separation alone. We discuss our results with regard to the inhomogeneous phases observed at the LaAlO3/SrTiO3 or LaTiO3/SrTiO3 interfaces. Y1 - 2015 UR - http://iopscience.iop.org/article/10.1209/0295-5075/109/17006;jsessionid=34AAE2057398BD7AE51C0C4719FC29DD.c2.iopscience.cld.iop.org U6 - https://doi.org/10.1209/0295-5075/109/17006 SN - 1286-4854 VL - 109 IS - 1 SP - 17006 ER - TY - GEN A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto T1 - Inhomogeneous Rashba spin–orbit coupling and intrinsic spin-Hall effect T2 - Journal of Magnetism and Magnetic Materials N2 - The spin-Hall effect is the generation of a transverse spin-current induced by a longitudinal electric field. Among the various scattering mechanisms which can induce a finite spin-Hall effect we focus on the intrinsic contribution arising from a Rashba-type spin–orbit (RSO) coupling which for couplings linear in momentum usually vanishes. Here we show that non-homogeneity in the spin–orbit coupling arising from structure inversion asymmetry gives rise to a finite spin-Hall effect which we exemplify for a system with striped Rashba spin–orbit coupling. KW - Spin Hall effect KW - Rashba spin–orbit coupling KW - Inhomogeneity Y1 - 2016 UR - http://www.sciencedirect.com/science/article/pii/S0304885316317772 U6 - https://doi.org/10.1016/j.jmmm.2016.12.066 VL - 440 SP - 63 EP - 65 ER - TY - GEN A1 - Capati, Matteo A1 - Caprara, Sergio A1 - Di Castro, Carlo A1 - Grilli, Marco A1 - Seibold, Götz A1 - Lorenzana, José T1 - Electronic polymers and soft-matter-like broken symmetries in underdoped cuprates T2 - Nature Communications N2 - Empirical evidence in heavy fermion, pnictide and other systems suggests that unconventional superconductivity appears associated to some form of real-space electronic order. For the cuprates, despite several proposals, the emergence of order in the phase diagram between the commensurate antiferromagnetic state and the superconducting state is not well understood. Here we show that in this regime doped holes assemble in ‘electronic polymers’. Within a Monte Carlo study, we find that in clean systems by lowering the temperature the polymer melt condenses first in a smectic state and then in a Wigner crystal both with the addition of inversion symmetry breaking. Disorder blurs the positional order leaving a robust inversion symmetry breaking and a nematic order, accompanied by vector chiral spin order and with the persistence of a thermodynamic transition. Such electronic phases, whose properties are reminiscent of soft-matter physics, produce charge and spin responses in good accord with experiments. KW - Molecular electronics KW - Polymers KW - Superconducting properties and materials Y1 - 2015 UR - http://www.nature.com/articles/ncomms8691 U6 - https://doi.org/doi:10.1038/ncomms8691 SN - 2041-1723 VL - 6 SP - 7691 ER - TY - CHAP A1 - Bill, Andreas A1 - Hizhnyakov, Vladimir A1 - Seibold, Götz ED - Bussmann-Holder, Annette ED - Keller, Hugo ED - Bianconi, Antonio T1 - Electronic Phase Separation and Electron–Phonon Coupling in Cuprate Superconductors T2 - High-Tc Copper Oxide Superconductors and Related Novel Materials N2 - Nanoscale electronic inhomogeneities are nowadays a well established feature of high-temperature superconductors, most prominently exemplified by the observation of charge-ordered states in a large number of cuprate materials. These inhomogeneities have profound consequences for the electron–phonon coupling since they allow for long-range pairing interactions due to the reduced screening supplemented by the enhancement of the electron–phonon vertex due to strong correlations. In this chapter we review the particular contribution of the Stuttgart-Tartu-Cottbus group to this field and discuss how the current status of experimental results provides affirmation to their ideas. KW - Strongly Correlated Systems KW - Optical and Electronic Materials KW - Nanochemistry KW - Ceramics KW - Spectroscopy and Microscopy KW - Superconductivity KW - Glass KW - Composites KW - Natural Materials Y1 - 2017 UR - http://link.springer.com/chapter/10.1007/978-3-319-52675-1_1 SN - 978-3-319-52674-4 SN - 978-3-319-52675-1 U6 - https://doi.org/10.1007/978-3-319-52675-1_1 SP - 1 EP - 14 PB - Springer International Publishing CY - Cham ER - TY - GEN A1 - Markiewicz, Richard S. A1 - Seibold, Götz A1 - Lorenzana, José A1 - Bansil, Arun T1 - Gutzwiller charge phase diagram of cuprates, including electron–phonon coupling effects T2 - New Journal of Physics N2 - Besides significant electronic correlations, high-temperature superconductors also show a strong coupling of electrons to a number of lattice modes. Combined with the experimental detection of electronic inhomogeneities and ordering phenomena in many high-Tc compounds, these features raise the question as to what extent phonons are involved in the associated instabilities. Here we address this problem based on the Hubbard model including a coupling to phonons in order to capture several salient features of the phase diagram of hole-doped cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard U near half-filling, are found to become active at a fairly low doping level. We find that possible charge order is mainly driven by Fermi surface nesting, with competition between a near-$(\pi ,\pi )$ order at low doping and antinodal nesting at higher doping, very similar to the momentum structure of magnetic fluctuations. The resulting nesting vectors are generally consistent with photoemission and tunneling observations, evidence for charge density wave order in YBa2Cu3O$_{7-\delta }$ including Kohn anomalies, and suggestions of competition between one- and two-q-vector nesting. Y1 - 2015 UR - http://iopscience.iop.org/article/10.1088/1367-2630/17/2/023074/meta U6 - https://doi.org/10.1088/1367-2630/17/2/023074 SN - 1367-2630 VL - 17 IS - 2 SP - 023074 ER - TY - GEN A1 - Caprara, Sergio A1 - Di Castro, Carlo A1 - Seibold, Götz A1 - Grilli, Marco T1 - Dynamical charge density waves rule the phase diagram of cuprates T2 - Physical Review B N2 - In the last few years, charge density waves (CDWs) have been ubiquitously observed in high-temperature superconducting cuprates and are now the most investigated among the competing orders in the still hot debate on these systems. A wealth of new experimental data raises several fundamental issues that challenge the various theoretical proposals. We here relate our mean-field instability line T0CDW of a strongly correlated Fermi liquid to the pseudogap T∗(p) line, marking in this way the onset of CDW-fluctuations. These fluctuations reduce strongly the mean-field critical line. Controlling this reduction via an infrared frequency cutoff related to the characteristic time of the probes, we account for the complex experimental temperature versus doping phase diagram. We provide a coherent scenario explaining why different CDW onset curves are observed by different experimental probes and seem to extrapolate at zero temperature into seemingly different quantum critical points (QCPs) in the intermediate and overdoped region. The nearly singular anisotropic scattering mediated by these fluctuations also accounts for the rapid changes of the Hall number seen in experiments and provides the first necessary step for a possible Fermi surface reconstruction fully establishing at lower doping. Finally, we show that phase fluctuations of the CDWs, which are enhanced in the presence of strong correlations near the Mott insulating phase, naturally account for the disappearance of the CDWs at low doping with yet another QCP as seen by the experiments. Y1 - 2017 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.224511 U6 - https://doi.org/https://doi.org/10.1103/PhysRevB.95.224511 SN - 2469-9950 SN - 2469-9969 VL - 95 IS - 22 SP - 224511 ER - TY - GEN A1 - Hokamp, Sascha A1 - Seibold, Götz T1 - Tax Compliance and Public Goods Provision An Agent-based Econophysics Approach T2 - Central European Journal of Economic Modelling and Econometrics N2 - We calculate the dynamics of tax evasion within a multi-agent econophysics model which is adopted from the theory of magnetism and previously has been shown to capture the main characteristics from agent-based based models which build on the standard Allingham and Sandmo approach. In particular, we implement a feedback of public goods provision on the decision-making of selfish agents which aim to pursue their self interest. Our results imply that such a feedback enhances the moral attitude of selfish agents thus reducing the percentage of tax evasion. Two parameters govern the behavior of selfish agents, (i) the rate of adaption to changes in public goods provision and (ii) the threshold of perception of public goods provision. Furtheron we analyze the tax evasion dynamics for different agent compositions and under the feedback of public goods provision. We conclude that policymakers may enhance tax compliance behavior via the threshold of perception by means of targeted public relations. Y1 - 2014 UR - http://cejeme.eu/publishedarticles/2014-35-24-635550501521093750-4578.pdf SN - 2080-0886 VL - 6 IS - 4 SP - 217 EP - 236 ER - TY - CHAP A1 - Hokamp, Sascha A1 - Seibold, Götz ED - Kaminski, Bogumil ED - Koloch, Grzegorz T1 - How Much Rationality Tolerates the Shadow Economy? – An Agent-Based Econophysics Approach T2 - Advances in social simulation : proceedings of the 9th Conference of the European Social Simulation Association N2 - We calculate the size of the shadow economy within a multi-agent econophysics model previously developed for the study of tax evasion. In particular, we analyze deviating behavior depending on the fraction of rational agents which aim to pursue their self interest. Two audit mechanisms are considered within our model, that are, (i) a constant compliance period which is enforced after black market activities of an agent have been detected and (ii) a backauditing method which determines the compliance period according to the particpation rate in the shadow economy within a previously preassigned time interval. We calibrate our simulation with respect to experimental evidence of tax compliance in France and Germany and give estimates for the percentage of selfish agents in these countries. This implies different policy recommendations that may work to fight the shadow economy, tax evasion, and the like. KW - shadow economy KW - econophysics KW - multi-agent model Y1 - 2014 UR - http://link.springer.com/chapter/10.1007/978-3-642-39829-2_11 SN - 978-3-642-39828-5 U6 - https://doi.org/10.1007/978-3-642-39829-2_11 SP - 128 PB - Springer CY - Berlin [u.a.] ER - TY - GEN A1 - Bovenzi, Nicandro A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto A1 - Scopigno, Niccolò A1 - Seibold, Götz T1 - Density inhomogeneities and Rashba spin-orbit coupling interplay in oxide interfaces T2 - Journal of Physics and Chemistry of Solids N2 - There is steadily increasing evidence that the two-dimensional electron gas (2DEG) formed at the interface of some insulating oxides like LaAlO3/SrTiO3 and LaTiO3/SrTiO3 is strongly inhomogeneous. The inhomogeneous distribution of electron density is accompanied by an inhomogeneous distribution of the (self-consistent) electric field confining the electrons at the interface. In turn this inhomogeneous transverse electric field induces an inhomogeneous Rashba spin-orbit coupling (RSOC). After an introductory summary on two mechanisms possibly giving rise to an electronic phase separation accounting for the above inhomogeneity, we introduce a phenomenological model to describe the density-dependent RSOC and its consequences. Besides being itself a possible source of inhomogeneity or charge-density waves, the density-dependent RSOC gives rise to interesting physical effects like the occurrence of inhomogeneous spin-current distributions and inhomogeneous quantum-Hall states with chiral “edge” states taking place in the bulk of the 2DEG. The inhomogeneous RSOC can also be exploited for spintronic devices since it can be used to produce a disorder-robust spin Hall effect. Y1 - 2017 UR - https://www.sciencedirect.com/science/article/pii/S0022369717305991 SN - 0022-3697 ER - TY - GEN A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Castellani, Claudio T1 - Application of the Mattis-Bardeen theory in strongly disordered superconductors T2 - Physical Review B N2 - The low-energy optical conductivity of conventional superconductors is usually well described by Mattis-Bardeen (MB) theory, which predicts the onset of absorption above an energy corresponding to twice the superconducing (SC) gap parameter Δ. Recent experiments on strongly disordered superconductors have challenged the application of the MB formulas due to the occurrence of additional spectral weight at low energies below 2Δ. Here we identify three crucial items that have to be included in the analysis of optical-conductivity data for these systems: (a) the correct identification of the optical threshold in the Mattis-Bardeen theory and its relation with the gap value extracted from the measured density of states, (b) the gauge-invariant evaluation of the current-current response function needed to account for the optical absorption by SC collective modes, and (c) the inclusion into the MB formula of the energy dependence of the density of states present already above Tc. By computing the optical conductivity in the disordered attractive Hubbard model, we analyze the relevance of all these items, and we provide a compelling scheme for the analysis and interpretation of the optical data in real materials. KW - Superconductivity KW - Superconductivity fluctuations KW - Impurities in superconductors Y1 - 2017 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.144507 U6 - https://doi.org/10.1103/PhysRevB.96.144507 VL - 96 IS - 14 SP - 144507 ER - TY - GEN A1 - Miao, Hu A1 - Lorenzana, José A1 - Seibold, Götz A1 - Peng, Yingying A1 - Amorese, Andrea A1 - Yakhou-Harris, Flora A1 - Kummer, Kurt A1 - Brookes, Nicholas B. A1 - Konik, R. M. A1 - Thampy, Vivek A1 - Gu, G. D. A1 - Ghiringhelli, Giacomo Claudio A1 - Braicovich, Lucio A1 - Dean, M. P. M. T1 - High-temperature charge density wave correlations in La1.875Ba0.125CuO4 without spin–charge locking T2 - Proceedings of the National Academy of Sciences of the United States of America PNAS N2 - Although all superconducting cuprates display charge-ordering tendencies, their low-temperature properties are distinct, impeding efforts to understand the phenomena within a single conceptual framework. While some systems exhibit stripes of charge and spin, with a locked periodicity, others host charge density waves (CDWs) without any obviously related spin order. Here we use resonant inelastic X-ray scattering to follow the evolution of charge correlations in the canonical stripe-ordered cuprate La1.875Ba0.125CuO4 across its ordering transition. We find that high-temperature charge correlations are unlocked from the wavevector of the spin correlations, signaling analogies to CDW phases in various other cuprates. This indicates that stripe order at low temperatures is stabilized by the coupling of otherwise independent charge and spin density waves, with important implications for the relation between charge and spin correlations in the cuprates. KW - charge density waves KW - stripes KW - high-temperature superconductivity KW - cuprates KW - X-rays Y1 - 2017 UR - http://www.pnas.org/content/early/2017/10/31/1708549114.abstract U6 - https://doi.org/10.1073/pnas.1708549114 SN - 1091-6490 SN - 0027-8424 VL - 114 IS - 47 SP - 12430 EP - 12435 ER - TY - GEN A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto T1 - Theory of the Spin Galvanic Effect at Oxide Interfaces T2 - Physical Review Letters N2 - The spin galvanic effect (SGE) describes the conversion of a nonequilibrium spin polarization into a transverse charge current. Recent experiments have demonstrated a large conversion efficiency for the two-dimensional electron gas formed at the interface between two insulating oxides, LaAlO3 and SrTiO3. Here, we analyze the SGE for oxide interfaces within a three-band model for the Ti t2g orbitals which displays an interesting variety of effective spin-orbit couplings in the individual bands that contribute differently to the spin-charge conversion. Our analytical approach is supplemented by a numerical treatment where we also investigate the influence of disorder and temperature, which turns out to be crucial to providing an appropriate description of the experimental data. KW - Spin polarization KW - Spin-orbit coupling KW - Spintronics KW - Two-dimensional electron gas Y1 - 2017 UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.256801 U6 - https://doi.org/10.1103/PhysRevLett.119.256801 SN - 1092-0145 VL - 119 IS - 25 ER - TY - GEN A1 - Bünemann, Jörg A1 - Seibold, Götz T1 - Charge and pairing dynamics in the attractive Hubbard model: Mode coupling and the validity of linear-response theory T2 - Physical Review B N2 - Pump-probe experiments have turned out as a powerful tool in order to study the dynamics of competing orders in a large variety of materials. The corresponding analysis of the data often relies on standard linear-response theory generalized to nonequilibrium situations. Here we examine the validity of such an approach for the charge and pairing response of systems with charge-density wave and (or) superconducting (SC) order. Our investigations are based on the attractive Hubbard model which we study within the time-dependent Hartree-Fock approximation. In particular, we calculate the quench and pump-probe dynamics for SC and charge order parameters in order to analyze the frequency spectra and the coupling of the probe field to the specific excitations. Our calculations reveal that the “linear-response assumption” is justified for small to moderate nonequilibrium situations (i.e., pump pulses) in the case of a purely charge-ordered ground state. However, the pump-probe dynamics on top of a superconducting ground state is determined by phase and amplitude modes which get coupled far from the equilibrium state indicating the failure of the linear-response assumption. KW - Charge density waves KW - Hartree-Fock methods KW - Hubbard model KW - Linear response theory KW - Mean field theory KW - Variational wave functional methods Y1 - 2017 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.245139 U6 - https://doi.org/10.1103/PhysRevB.96.245139 SN - 2469-9977 SN - 1538-4489 VL - 96 IS - 24 ER - TY - CHAP A1 - Seibold, Götz ED - Hokamp, Sascha ED - Gulyas, Lazlo ED - Koehler, Matthew ED - Wijesinghe, Sanith T1 - From Spins to Agents: An Econophysics Approach to Tax Evasion T2 - Agent-based Modeling of Tax Evasion: Theoretical Aspects and Computational Simulations N2 - The only single-source guide to understanding, using, adapting, and designing state-of-the-art agent-based modeling of tax evasion A computational method for simulating the behaviour of individuals or groups and their effects on an entire system, agent-based modeling has proven itself to be a powerful new tool for detecting tax fraud. While interdisciplinary groups and individuals working in the tax domain have published numerous articles in diverse peer-reviewed journals and presented their findings at international conferences, until Agent-based Modeling of Tax Evasion there has been no authoritative, single-source guide to state-of-the-art agent-based tax evasion modeling techniques and technologies. Featuring contributions from distinguished experts in the field from around the globe, Agent-Based Modeling of Tax Evasion provides in-depth coverage of an array of field tested agent-based tax evasion models. Models are presented in a unified format so as to enable readers to systematically work their way through the various modeling alternatives available to them. Three main components of each agent-based model are explored in accordance with the Overview, Design Concepts, and Details (ODD) protocol, each section of which contains several sub elements that help to illustrate the model clearly and that assist readers in replicating the modeling results described. Presents models in a unified and structured manner to provide a point of reference for readers interested in agent-based modeling of tax evasion Explores the theoretical aspects and diversity of agent-based modeling through the example of tax evasion Provides an overview of the characteristics of more than thirty agent-based tax evasion frameworks Functions as a solid foundation for lectures and seminars on agent-based modeling of tax evasion The only comprehensive treatment of agent-based tax evasion models and their applications, this book is an indispensable working resource for practitioners and tax evasion modelers both in the agent-based computational domain and using other methodologies. It is also an excellent pedagogical resource for teaching tax evasion modeling and/or agent-based modeling generally. KW - General & Introductory Statistics KW - Applied Probability & Statistics Statistics for Finance" Business & Economics KW - Statistics for Finance" Business & Economics Y1 - 2018 SN - 978-1-119-15570-6 SP - 315 EP - 336 PB - Wiley CY - Weinheim ER - TY - GEN A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Grilli, Marco A1 - Raimondi, Roberto T1 - On the Evaluation of the Spin Galvanic Effect in Lattice Models with Rashba Spin-Orbit Coupling T2 - Condensed matter N2 - The spin galvanic effect (SGE) describes the conversion of a non-equilibrium spin polarization into a charge current and has recently attracted renewed interest due to the large conversion efficiency observed in oxide interfaces. An important factor in the SGE theory is disorder which ensures the stationarity of the conversion. Through this paper, we propose a procedure for the evaluation of the SGE on disordered lattices which can also be readily implemented for multiband systems. We demonstrate the performance of the method for a single-band Rashba model and compare our results with those obtained within the self-consistent Born approximation for a continuum model. KW - spintronics KW - spin-galvanic effect KW - lattice models Y1 - 2018 UR - http://www.mdpi.com/2410-3896/3/3/22 U6 - https://doi.org/10.3390/condmat3030022 SN - 2410-3896 VL - 3 IS - 33 SP - 1 EP - 10 ER - TY - CHAP A1 - Seibold, Götz A1 - Caprara, Sergio A1 - Raimondi, Roberto ED - Drouhin, Henri-Jean ED - Wegrowe, Jean-Eric ED - Razeghi, Manijeh ED - Jaffrès, Henri T1 - Theory of charge-spin conversion at oxide interfaces: the inverse spin-galvanic effect T2 - Spintronics XI, SPIE Nanoscience + Engineering, 19-23 August 2018, San Diego, California, United States N2 - We evaluate the non-equilibrium spin polarization induced by an applied electric field for a tight-binding model of electron states at oxides interfaces in LAO/STO heterostructures. By a combination of analytic and numerical approaches we investigate how the spin texture of the electron eigenstates due to the interplay of spin-orbit coupling and inversion asymmetry determines the sign of the induced spin polarization as a function of the chemical potential or band filling, both in the absence and presence of local disorder. With the latter, we find that the induced spin polarization evolves from a non monotonous behavior at zero temperature to a monotonous one at higher temperature. Our results may provide a sound framework for the interpretation of recent experiments. Y1 - 2018 UR - https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10732/107322P/Theory-of-charge-spin-conversion-at-oxide-interfaces--the/10.1117/12.2319592.short U6 - https://doi.org/10.1117/12.2319592 PB - Spie CY - Bellingham, USA ER - TY - GEN A1 - Martens, Christian A1 - Bill, Andreas A1 - Seibold, Götz T1 - Phase separation and proximity effects in itinerant ferromagnet/superconductor heterostructures T2 - Physical Review B N2 - Heterostructures made of itinerant ferromagnets and superconductors are studied. In contrast to most previous models, ferromagnetism is not enforced by an effective Zeeman field but induced in a correlated single-band model (CSBM) that displays itinerant ferromagnetism as a mean-field ground state. In this model superconductivity and magnetism are both calculated self-consistently. We calculate the magnitude of the magnetization, the superconducting correlations, and variations of the charge density self-consistently for a superconducting-magnetic bilayer by solving the Bogoliubov–de Gennes equations on a two-dimensional lattice. We determine all three quantities as a function of the Coulomb repulsion U and the ferromagnetic exchange interaction J. The CSBM displays a variety of features not present in the Zeeman exchange model—for example, the occurrence of electronic phase separation and the competition of magnetic and superconducting orders far away from the interface. KW - charge order KW - Exchange interaction KW - Ferromagnetism KW - Local density of states KW - Microphase separation KW - Proximity effect KW - Superconducting order parameter Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevB.98.174513 SN - 2469-9969 SN - 1095-3795 VL - 98 IS - 17 ER - TY - GEN A1 - Miao, Hu A1 - Fumagalli, Roberto A1 - Rossi, M. A1 - Lorenzana, José A1 - Seibold, Götz A1 - Yakhou-Harris, Flora A1 - Kummer, K. A1 - Brookes, Nicholas B. A1 - Gu, G. D. A1 - Braicovich, Lucio A1 - Ghiringhelli, Giacomo Claudio A1 - Dean, M. P. M. T1 - Formation of Incommensurate Charge Density Waves in Cuprates T2 - Physical Review X N2 - Although charge density waves (CDWs) are omnipresent in cuprate high-temperature superconductors, they occur at significantly different wave vectors, confounding efforts to understand their formation mechanism. Here, we use resonant inelastic x-ray scattering to investigate the doping- and temperature-dependent CDW evolution in La₂₋ₓBaₓCuO₄ (x=0.115–0.155). We discover that the CDW develops in two stages with decreasing temperature. A precursor CDW with a quasicommensurate wave vector emerges first at high temperature. This doping-independent precursor CDW correlation originates from the CDW phase mode coupled with a phonon and “seeds” the low-temperature CDW with a strongly doping-dependent wave vector. Our observation reveals the precursor CDW and its phase mode as the building blocks of the highly intertwined electronic ground state in the cuprates. KW - Research Areas Charge density waves KW - Electrical Properties KW - Cuprates KW - Strongly correlated systems KW - Resonant inelastic x-ray scattering KW - Superconductivity Y1 - 2019 UR - https://journals.aps.org/prx/abstract/10.1103/PhysRevX.9.031042 U6 - https://doi.org/10.1103/PhysRevX.9.031042 SN - 2160-3308 VL - 9 IS - 3 SP - 031042-1 EP - 031042-11 ER - TY - RPRT A1 - Noell, M. A1 - Seibold, Götz A1 - Krebs, Andreas T1 - Excitations in disordered superconductors: Inclusion of long-range Coulomb interactions Y1 - 2019 UR - https://www.hlrn.de/HLRN-Report-2019.pdf SN - 978-3-00-063360-7 SP - 269 PB - HLRN CY - Berlin ER - TY - GEN A1 - Noatschk, Katharina A1 - Martens, Christian A1 - Seibold, Götz T1 - Time-Dependent Gutzwiller Approximation: Theory and Applications T2 - Journal of Superconductivity and Novel Magnetism N2 - The time-dependent Gutzwiller approximation is rederived on the basis of a variational wave function which is a direct product of a Slater determinant and a coherent state. The latter can be related to the slave-boson formulation by Kotliar and Ruckenstein, and our approach offers a convenient way to generalize the theory towards the implementation of symmetry-broken states and the study of non-equilibrium phenomena. We discuss the concept with regard to applications in the linear response limit and for quenched antiferromagnetic order for which we evaluate the optical conductivity in non-equilibrium situations. KW - Hubbard model KW - Gutzwiller approximation KW - Non-equilibrium Y1 - 2020 UR - https://link.springer.com/article/10.1007/s10948-019-05406-z#Sec1 U6 - https://doi.org/10.1007/s10948-019-05406-z VL - 33 IS - 8 SP - 2389 EP - 2393 ER - TY - GEN A1 - Seibold, Götz A1 - Lorenzana, Jose T1 - Nonequilibrium dynamics from BCS to the bosonic limit T2 - Physical Review B N2 - Within the time-dependent Gutzwiller approximation applied to the negative-U Hubbard model, we investigate the dynamics of a superconductor after an interaction quench for different values of the final interaction from weak to strong coupling. The equilibrium BCS-BEC crossover becomes a sharp transition in the out-of-equilibrium dynamics between weak- and strong-coupling dynamical phases. Two different frequencies (ΩJ<ΩU) dominate the order parameter dynamics. In the weak coupling phase, ΩJ follows twice the asymptotic average value of the gap (ΩJ≈2Δ∞) and ΩU is much larger but hardy visible in the anomalous density. At long times the BCS dynamics is recovered but surprisingly differences remain during the transient phase. In the strong coupling phase, the dynamics decouples from the asymptotic value of the order parameter except at exactly half filling and close to the dynamical transition where ΩU≈2Δ∞. The out-of-equilibrium transient spectral density and optical conductivity are presented and discussed in relation to pump probe experiments. Both ΩJ and ΩU give rise to a complex structure of self-driven slow Rabi oscillations which are visible in the nonequilibrium optical conductivity where also sidebands appear due to the modulation of the double occupancy by superconducting amplitude oscillations. Analogous results apply to CDW and SDW systems. Our results show that in systems with long coherence times, pump-probe experiments allow us to characterize the regime (BCS vs preformed pairs) through very specific out-of-equilibrium fingerprints. KW - BEC-BCS crossover KW - Superconductivity fluctuations KW - Superconductivity Y1 - 2020 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.102.144502 U6 - https://doi.org/10.1103/PhysRevB.102.144502 SN - 2469-9969 VL - 102 IS - 14 ER - TY - GEN A1 - Bill, Andreas A1 - Hizhnyakov, Vladimir A1 - Kremer, Reinhard K. A1 - Seibold, Götz A1 - Shelkan, Aleksander A1 - Sherman, Aleksei T1 - Phase Separation and Pairing Fluctuations in Oxide Materials T2 - Condensed Matter N2 - The microscopic mechanism of charge instabilities and the formation of inhomogeneous states in systems with strong electron correlations is investigated. We demonstrate that within a strong coupling expansion the single-band Hubbard model shows an instability towards phase separation and extend the approach also for an analysis of phase separation in the Hubbard-Kanamori hamiltonian as a prototypical multiband model. We study the pairing fluctuations on top of an inhomogeneous stripe state where superconducting correlations in the extended s-wave and d-wave channels correspond to (anti)bound states in the two-particle spectra. Whereas extended s-wave fluctuations are relevant on the scale of the local interaction parameter U, we find that d-wave fluctuations are pronounced in the energy range of the active subband which crosses the Fermi level. As a result, low energy spin and charge fluctuations can transfer the d-wave correlations from the bound states to the low energy quasiparticle bands. Our investigations therefore help to understand the coexistence of stripe correlations and d-wave superconductivity in cuprates. KW - phase separation KW - cuprate superconductors KW - electronic correlations Y1 - 2020 UR - https://www.mdpi.com/2410-3896/5/4/65/htm U6 - https://doi.org/10.3390/condmat5040065 SN - 2410-3896 VL - 5 IS - 4 ER - TY - GEN A1 - Seibold, Götz A1 - Arpaia, Riccardo A1 - Ying Ying, Peng A1 - Fumagalli, Roberto A1 - Braicovich, Lucio A1 - Di Castro, Carlo A1 - Grilli, Marco A1 - Ghiringhelli, Giacomo Claudio A1 - Caprara, Sergio T1 - Strange metal behaviour from charge density fluctuations in cuprates T2 - Communications Physics N2 - Besides the mechanism responsible for high critical temperature superconductivity, the grand unresolved issue of the cuprates is the occurrence of a strange metallic state above the so-called pseudogap temperature T*. Even though such state has been successfully described within a phenomenological scheme, the so-called Marginal Fermi-Liquid theory, a microscopic explanation is still missing. However, recent resonant X-ray scattering experiments identified a new class of charge density fluctuations characterized by low characteristic energies and short correlation lengths, which are related to the well-known charge density waves. These fluctuations are present over a wide region of the temperature-vs-doping phase diagram and extend well above T*. Here we investigate the consequences of charge density fluctuations on the electron and transport properties and find that they can explain the strange metal phenomenology. Therefore, charge density fluctuations are likely the long-sought microscopic mechanism underlying the peculiarities of the metallic state of cuprates. KW - Electronic properties and materials KW - Superconducting properties and materials Y1 - 2021 UR - https://www.nature.com/articles/s42005-020-00505-z U6 - https://doi.org/10.1038/s42005-020-00505-z SN - 2399-3650 VL - 4 SP - 1 EP - 6 ER - TY - GEN A1 - Seibold, Götz A1 - Udina, Mattia A1 - Castellani, Claudio A1 - Benfatto, Lara T1 - Third harmonic generation from collective modes in disordered superconductors T2 - Physical Review B N2 - Recent experiments with strong THz fields in both conventional and unconventional superconductors have clearly evidenced a marked third-harmonic generation below the superconducting temperature Tc. Its interpretation challenged substantial theoretical work aimed at establishing the relative efficiency of quasiparticle excitations and collective modes in triggering such a resonant response. Here we compute the nonlinear current by implementing a time-dependent Bogoljubov–de Gennes approach, with the twofold aim to account nonperturbatively for the effect of local disorder, and to include the contribution of all collective modes, i.e., superconducting amplitude (Higgs) and phase fluctuations, and charge fluctuations. We show that, in agreement with previous work, already at small disorder the quasiparticle response is dominated by paramagnetic effects. We further demonstrate that paramagnetic processes mediate also the response of all collective modes, with a substantial contribution of charge/phase fluctuations. These processes, which have been overlooked so far, turn out to dominate the third-order current at strong disorder. In addition, we show that disorder strongly influences the polarization dependence of the nonlinear response, with a marked difference between the clean and the disordered case. Our results are particularly relevant for recent experiments in cuprates, whose band structure is in a first approximation reproduced by our lattice model. KW - High-order harmonic generation KW - Impurities in superconductors KW - Optical & microwave phenomena KW - Quasiparticles & collective excitations KW - Superconductivity KW - Disordered systems KW - Higgs bosons KW - Bogoliubov-de Gennes equations Y1 - 2021 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.103.014512 U6 - https://doi.org/10.1103/PhysRevB.103.014512 VL - 103 IS - 1 ER - TY - GEN A1 - Noatschk, Katharina A1 - Hofmann, E. V. S. A1 - Dabrowski, Jarek Marek A1 - Curson, Neil J. A1 - Schröder, Thomas A1 - Klesse, Wolfgang Matthias A1 - Seibold, Götz T1 - Ge(001) surface reconstruction with Sn impurities T2 - Surface Science N2 - Defects play an important role for surface reconstructions and therefore also influence the substrate growth. In this work we present a first principle calculation for the Ge(001) surface without and with tin impurities incorporated into the top surface layer. By mapping the system onto an Ising-type model, with interaction constants taken from density functional theory, the stability of the surface reconstructions under the influence of different concentrations of tin impurities is explored. This approach allows us to simulate the possible phase transitions for the different surface reconstructions including the local structure around the tin impurity atoms. In addition, we compare our theoretical results with experimental STM images on clean and Sn-doped Ge(100) surfaces. KW - Gesn KW - DFT KW - Monte carlo simulations KW - Surface reconstruction KW - Impurities Y1 - 2021 UR - https://www.sciencedirect.com/science/article/pii/S0039602821001163?dgcid=author U6 - https://doi.org/10.1016/j.susc.2021.121912 VL - 713 SP - 1 EP - 8 ER - TY - GEN A1 - Wahlberg, Eric A1 - Arpaia, Riccardo A1 - Seibold, Götz A1 - Rossi, Matteo A1 - Fumagalli, Roberto A1 - Trabaldo, Edoardo A1 - Brookes, Nicholas B. A1 - Braicovich, Lucio A1 - Caprara, Sergio A1 - Lombardi, Floriana A1 - Gran, Ulf A1 - Ghiringhelli, Giacomo Claudio A1 - Bauch, Thilo T1 - Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7–δ T2 - Science N2 - The normal state of optimally doped cuprates is dominated by the “strange metal” phase that shows a linear temperature (T) dependence of the resistivity persisting down to the lowest T. For underdoped cuprates, this behavior is lost below the pseudogap temperature T*, where charge density waves (CDWs), together with other intertwined local orders, characterize the ground state. We found that the T-linear resistivity of highly strained, ultrathin, underdoped YBa2Cu3O7–δ films is restored when the CDW amplitude, detected by resonant inelastic x-ray scattering, is suppressed. This observation suggests an intimate connection between the onset of CDWs and the departure from T-linear resistivity in underdoped cuprates. Our results illustrate the potential of using strain control to manipulate the ground state of quantum materials. KW - Cuprate superconductors KW - Charge-Density Wave Y1 - 2021 UR - https://www.science.org/doi/10.1126/science.abc8372 U6 - https://doi.org/10.1126/science.abc8372 VL - 373 IS - 6562 SP - 1506 EP - 1510 ER - TY - GEN A1 - Martens, Christian A1 - Seibold, Götz T1 - Non-equilibrium dynamics of stripes in cuprate superconductors T2 - Journal of Magnetism and Magnetic Materials N2 - We use the time-dependent Gutzwiller approximation for the single-band Hubbard model to analyze the non-equilibrium dynamics for stripe ground states. In particular, we are interested in the interplay between spin and charge dynamics which is analyzed by quenching the system either in the charge or spin sector. This allows us to investigate the coupled relaxation dynamics as a function of the supplied energy. Further insight is provided by mapping the Gutzwiller dynamics onto a time-dependent Landau approach which lacks the double occupancy contribution to the time-evolution but allows to tune the coupling between spin- and charge degrees of freedom. KW - Hubbard model KW - Gutzwiller approximation KW - Landau KW - Non-equilibrium KW - Charge order KW - Spin order Y1 - 2022 UR - https://www.sciencedirect.com/science/article/pii/S030488532100812X U6 - https://doi.org/10.1016/j.jmmm.2021.168565 SN - 1873-4766 VL - 543 SP - 1 EP - 4 ER - TY - GEN A1 - Caprara, Sergio A1 - Di Castro, Carlo A1 - Mirarchi, Giovanni A1 - Seibold, Götz A1 - Grilli, Marco T1 - Dissipation-driven strange metal behavior T2 - Communications Physics N2 - Anomalous metallic properties are often observed in the proximity of quantum critical points, with violation of the Fermi Liquid paradigm. We propose a scenario where, near the quantum critical point, dynamical fluctuations of the order parameter with finite correlation length mediate a nearly isotropic scattering among the quasiparticles over the entire Fermi surface. This scattering produces a strange metallic behavior, which is extended to the lowest temperatures by an increase of the damping of the fluctuations. We phenomenologically identify one single parameter ruling this increasing damping when the temperature decreases, accounting for both the linear-in-temperature resistivity and the seemingly divergent specific heat observed, e.g., in high-temperature superconducting cuprates and some heavy-fermion metals. KW - Electronic properties and materials KW - Superconducting properties and materials Y1 - 2022 UR - https://www.nature.com/articles/s42005-021-00786-y U6 - https://doi.org/10.1038/s42005-021-00786-y SN - 2399-3650 IS - 5 SP - 1 EP - 7 ER - TY - GEN A1 - Mirarchi, Giovanni A1 - Seibold, Götz A1 - Di Castro, Carlo A1 - Grilli, Marco A1 - Caprara, Sergio T1 - The Strange-Metal Behavior of Cuprates T2 - Condensed Matter N2 - Recent resonant X-ray scattering experiments on cuprates allowed to identify a new kind of collective excitations, known as charge density fluctuations, which have finite characteristic wave vector, short correlation length and small characteristic energy. It was then shown that these fluctuations provide a microscopic scattering mechanism that accounts for the anomalous transport properties of cuprates in the so-called strange-metal phase and are a source of anomalies in the specific heat. In this work, we retrace the main steps that led us to attributing a central role to charge density fluctuations in the strange-metal phase of cuprates, discuss the state of the art on the issue and provide an in-depth analysis of the contribution of charge density fluctuations to the specific heat. KW - high-temperature superconductors KW - cuprates KW - charge density fluctuations KW - strange metal KW - dynamical quantum criticality Y1 - 2022 UR - https://www.mdpi.com/2410-3896/7/1/29/htm U6 - https://doi.org/10.3390/condmat7010029 SN - 2410-3896 VL - 7 IS - 1 SP - 1 EP - 17 ER - TY - GEN A1 - Seibold, Götz A1 - Castellani, Claudio A1 - Lorenzana, José T1 - Adiabatic transition from a BCS superconductor to a Fermi liquid and phase dynamics T2 - Physical Review B N2 - We investigate the physics of an adiabatic transition from a BCS superconductor to a Fermi liquid for an exponentially slow decreasing pairing interaction. We show that, depending on the order of the thermodynamic limit and large times, a situation can arise in which the Fermi liquid keeps a memory of the parent BCS state. Furthermore, a time inversion of the interaction, supplemented by a manipulation analogous to a spin-/photon-echo experiment, allows us to recover the parent BCS state. Moreover, we study the evolution of the order parameter phase ϕ in transforming the BCS superconductor to a conventional metal. Since the global phase is the conjugate variable of the density, we explicitly show how to use the dynamics of ϕ together with gauge invariance to build up the noninteracting chemical potential away from particle-hole symmetry. We further analyze the role of ϕ in restoring the gauge-invariant current response when the noninteracting Fermi liquid is approached starting from a BCS superconductor in the presence of an external vector field. KW - Superconductivity KW - Nonequilibrium systems KW - Adiabatic approximation KW - BCS theory KW - Gauge symmetries KW - Variational approach Y1 - 2022 UR - https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.184513 U6 - https://doi.org/10.1103/PhysRevB.105.184513 SN - 2469-9969 VL - 105 IS - 18 SP - 184513-1 EP - 184513-14 ER - TY - GEN A1 - Udina, Mattia A1 - Fioro, Jacopo A1 - Cea, Tommaso A1 - Castellani, Claudio A1 - Seibold, Götz A1 - Benfatto, Lara T1 - THz non-linear optical response in cuprates: predominance of the BCS response over the Higgs mode T2 - Faraday Discussions N2 - Recent experiments with strong THz fields in unconventional cuprate superconductors have clearly evidenced an increase of the non-linear optical response below the superconducting critical temperature Tc. As in the case of conventional superconductors, a theoretical estimate of the various effects contributing to the non-linear response is needed in order to interpret the experimental findings. Here, we report a detailed quantitative analysis of the non-linear THz optical kernel in cuprates within a realistic model, accounting for the band structure and disorder level appropriate for these systems. We show that the BCS quasiparticle response is the dominant contribution for cuprates, and its polarization dependence accounts very well for the third-harmonic generation measurements. On the other hand, the polarization dependence of the THz Kerr effect is only partly captured by our calculations, suggesting the presence of additional effects when the system is probed using light pulses with different central frequencies. Y1 - 2022 UR - https://pubs.rsc.org/en/content/articlelanding/2022/FD/D2FD00016D U6 - https://doi.org/10.1039/D2FD00016D SN - 1364-5498 VL - 237 SP - 168 EP - 185 ER - TY - GEN A1 - Mirarchi, Giovanni A1 - Grilli, Marco A1 - Seibold, Götz A1 - Caprara, Sergio T1 - The Shrinking Fermi Liquid Scenario for Strange-Metal Behavior from Overdamped Optical Phonons T2 - Condensed Matter N2 - We discuss how the interaction of electrons with an overdamped optical phonon can give rise to a strange-metal behavior over extended temperature and frequency ranges. Although the mode has a finite frequency, an increasing damping shifts spectral weight to progressively lower energies so that despite the ultimate Fermi liquid character of the system at the lowest temperatures and frequencies, the transport and optical properties of the electron system mimic a marginal Fermi liquid behavior. Within this shrinking Fermi liquid scenario, we extensively investigate the electron self-energy in all frequency and temperature ranges, emphasizing similarities and differences with respect to the marginal Fermi liquid scenario. KW - strange-metal behavior KW - marginal Fermi liquid KW - high-temperature cuprate superconductors Y1 - 2024 UR - https://www.mdpi.com/2410-3896/9/1/14 U6 - https://doi.org/10.3390/condmat9010014 SN - 2410-3896 VL - 9 IS - 1 SP - 1 EP - 13 ER - TY - GEN A1 - Katsumi, Kota A1 - Fiore, Jacopo A1 - Udina, Mattia A1 - Romero, Ralph A1 - Barbalas, David A1 - Jesudasan, John A1 - Raychaudhuri, Pratap A1 - Seibold, Götz A1 - Benfatto, Lara A1 - Armitage, N. P. T1 - Revealing novel aspects of light-matter coupling by Terahertz Two-Dimensional Coherent Spectroscopy: the case of the amplitude mode in superconductors T2 - Physical Review Letters N2 - Recently developed terahertz (THz) two-dimensional coherent spectroscopy (2DCS) is a powerful technique to obtain materials information in a fashion qualitatively different from other spectroscopies. Here, we utilized THz 2DCS to investigate the THz nonlinear response of conventional superconductor NbN. Using broadband THz pulses as light sources, we observed a third-order nonlinear signal whose spectral components are peaked at twice the superconducting gap energy 2⁢Δ. With narrow-band THz pulses, a THz nonlinear signal was identified at the driving frequency Ω and exhibited a resonant enhancement at temperature when Ω=2⁢Δ. General theoretical considerations show that such a resonance can arise only from a disorder-activated paramagnetic coupling between the light and the electronic current. This proves that the nonlinear THz response can access processes distinct from the diamagnetic Raman-like density fluctuations, which are believed to dominate the nonlinear response at optical frequencies in metals. Our numerical simulations reveal that, even for a small amount of disorder, the Ω=2⁢Δ resonance is dominated by the superconducting amplitude mode over the entire investigated disorder range. This is in contrast to other resonances, whose amplitude-mode contribution depends on disorder. Our findings demonstrate the unique ability of THz 2DCS to explore collective excitations inaccessible in other spectroscopies. Y1 - 2024 UR - https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.132.256903 U6 - https://doi.org/10.1103/PhysRevLett.132.256903 VL - 132 ER - TY - GEN A1 - Caprara, Sergio A1 - Di Castro, Carlo A1 - Mirarchi, Giovanni A1 - Seibold, Götz A1 - Grilli, Marco T1 - The shrinking fermi liquid scenario for cuprates under the scrutiny of optical conductivity measurements T2 - Materials N2 - In a recent paper [B. Michon et al., Nat. Commun. (2023) 14:3033], optical conductivity experiments in cuprate superconductors were shown to display scaling properties consistent with the Marginal Fermi Liquid theory. Here, we argue that the temperature regime studied in these experiments does not allow for distinguishing between Marginal Fermi Liquid and Shrinking Fermi Liquid. In the latter scenario, which we recently proposed and which applies near a quantum critical point, dynamical fluctuations of the order parameter with a short correlation length mediate a nearly isotropic scattering among the quasiparticles over the entire Fermi surface leading to strange metal behavior. If the damping of these nearly local fluctuations increases by decreasing the temperature, the Fermi liquid regime shrinks and the strange metal behavior is extended to the lowest temperatures. This Shrinking Fermi Liquid scenario has many similarities and some differences with respect to the Marginal Fermi Liquid theory. In particular, we show that the approximate scaling properties of the optical conductivity in some high-frequency regimes predicted by the Shrinking Fermi Liquid scenario account for a very good description of the experimental data. Y1 - 2024 U6 - https://doi.org/10.3390/ma17235849 SN - 1996-1944 VL - 17 IS - 23 PB - MDPI AG ER -