@misc{CeaBucheliSeiboldetal., author = {Cea, Tommaso and Bucheli, Daniel and Seibold, G{\"o}tz and Benfatto, Lara and Lorenzana, Jos{\´e} and Castellani, Claudio}, title = {Optical excitation of phase modes in strongly disordered superconductors}, series = {Physical Review B}, volume = {89}, journal = {Physical Review B}, issn = {2469-9969}, doi = {10.1103/PhysRevB.89.174506}, pages = {174506}, abstract = {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.}, language = {en} } @misc{BucheliGrilliPeronacietal., author = {Bucheli, Daniel and Grilli, Marco and Peronaci, F. and Seibold, G{\"o}tz and Caprara, Sergio}, title = {Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling}, series = {Physical Review B}, volume = {89}, journal = {Physical Review B}, issn = {2469-9969}, doi = {10.1103/PhysRevB.89.195448}, abstract = {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.}, language = {en} } @misc{SeiboldDiCastroGrillietal., author = {Seibold, G{\"o}tz and Di Castro, Carlo and Grilli, Marco and Lorenzana, Jos{\´e}}, title = {Spin excitations of ferronematic order in underdoped cuprate superconductors}, series = {Scientific reports}, journal = {Scientific reports}, number = {4}, issn = {2045-2322}, doi = {10.1038/srep05319}, pages = {5319}, abstract = {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.}, language = {en} } @misc{SeiboldMarkiewiczLorenzana, author = {Seibold, G{\"o}tz and Markiewicz, Richard S. and Lorenzana, Jos{\´e}}, title = {Magnetic Structure of Electronic Inhomogeneities in Cuprates: Competition between Stripes and Spirals}, series = {Acta Physica Polonica A}, volume = {121}, journal = {Acta Physica Polonica A}, number = {5-6}, issn = {1898-794X}, pages = {1019 -- 1021}, abstract = {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.}, language = {en} } @misc{SeiboldMarkiewiczLorenzana, author = {Seibold, G{\"o}tz and Markiewicz, Richard S. and Lorenzana, Jos{\´e}}, title = {Stripes with Spin Canting in the Three-Band Hubbard Model}, series = {Journal of Superconductivity and Novel Magnetism}, volume = {26}, journal = {Journal of Superconductivity and Novel Magnetism}, number = {1}, issn = {1557-1939}, doi = {10.1007/s10948-012-1701-3}, pages = {49 -- 52}, abstract = {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.}, language = {en} } @misc{LemarieKamlapureBenfattoetal., author = {Lemari{\´e}, Gabriel and Kamlapure, Anand and Benfatto, Lara and Lorenzana, Jos{\´e} and Seibold, G{\"o}tz and Ganguli, S. C. and Raychaudhuri, Pratap and Castellani, Claudio}, title = {Universal scaling of the order-parameter distribution in strongly disordered superconductors}, series = {Physical Review B}, volume = {87}, journal = {Physical Review B}, number = {18}, issn = {2469-9977}, doi = {10.1103/PhysRevB.87.184509}, pages = {184509}, abstract = {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.}, language = {en} } @misc{SeiboldCapatiGrillietal., author = {Seibold, G{\"o}tz and Capati, Matteo and Grilli, Marco and Di Castro, Carlo and Grilli, Marco and Lorenzana, Jos{\´e}}, title = {Hidden ferronematic order in underdoped cuprates}, series = {Physical Review B}, volume = {87}, journal = {Physical Review B}, number = {3}, issn = {2469-9969}, doi = {10.1103/PhysRevB.87.035138}, pages = {035138}, abstract = {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.}, language = {en} } @misc{SeiboldPickhardt, author = {Seibold, G{\"o}tz and Pickhardt, Michael}, title = {Lapse of time effects on tax evasion in an agent-based econophysics model}, series = {Physica A: Statistical Mechanics and its Applications}, volume = {392}, journal = {Physica A: Statistical Mechanics and its Applications}, number = {9}, issn = {0378-4371}, doi = {10.1016/j.physa.2013.01.016}, pages = {2079 -- 2087}, abstract = {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.}, language = {en} } @misc{PickhardtSeibold, author = {Pickhardt, Michael and Seibold, G{\"o}tz}, title = {Income tax evasion dynamics: Evidence from an agent-based econophysics model}, series = {Journal of Economic Psychology}, volume = {40}, journal = {Journal of Economic Psychology}, issn = {0167-4870}, doi = {10.1016/j.joep.2013.01.011}, pages = {147 -- 160}, abstract = {• 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.}, language = {en} } @misc{BuenemannCaponeLorenzanaetal., author = {B{\"u}nemann, J{\"o}rg and Capone, Michael and Lorenzana, Jos{\´e} and Seibold, G{\"o}tz}, title = {Linear-response dynamics from the time-dependent Gutzwiller approximation}, series = {New Journal of Physics}, volume = {15}, journal = {New Journal of Physics}, issn = {1367-2630}, abstract = {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.}, language = {en} }