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 -