@misc{SeiboldCapraraGrillietal., author = {Seibold, G{\"o}tz and Caprara, Sergio and Grilli, Marco and Raimondi, Roberto}, title = {On the Evaluation of the Spin Galvanic Effect in Lattice Models with Rashba Spin-Orbit Coupling}, series = {Condensed matter}, volume = {3}, journal = {Condensed matter}, number = {33}, issn = {2410-3896}, doi = {10.3390/condmat3030022}, pages = {1 -- 10}, abstract = {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.}, language = {en} } @misc{CapraraDiCastroSeiboldetal., author = {Caprara, Sergio and Di Castro, Carlo and Seibold, G{\"o}tz and Grilli, Marco}, title = {Dynamical charge density waves rule the phase diagram of cuprates}, series = {Physical Review B}, volume = {95}, journal = {Physical Review B}, number = {22}, issn = {2469-9950}, doi = {https://doi.org/10.1103/PhysRevB.95.224511}, pages = {224511}, abstract = {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.}, language = {en} } @inproceedings{SeiboldCapraraRaimondi, author = {Seibold, G{\"o}tz and Caprara, Sergio and Raimondi, Roberto}, title = {Theory of charge-spin conversion at oxide interfaces: the inverse spin-galvanic effect}, series = {Spintronics XI, SPIE Nanoscience + Engineering, 19-23 August 2018, San Diego, California, United States}, booktitle = {Spintronics XI, SPIE Nanoscience + Engineering, 19-23 August 2018, San Diego, California, United States}, editor = {Drouhin, Henri-Jean and Wegrowe, Jean-Eric and Razeghi, Manijeh and Jaffr{\`e}s, Henri}, publisher = {Spie}, address = {Bellingham, USA}, doi = {10.1117/12.2319592}, abstract = {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.}, language = {en} } @misc{BovenziFinocchiaroScopignoetal., author = {Bovenzi, Nicolo and Finocchiaro, Francesca and Scopigno, Nicantro and Bucheli, Daniel and Caprara, Sergio and Seibold, G{\"o}tz and Grilli, Marco}, title = {Possible Mechanisms of Electronic Phase Separation in Oxide Interfaces}, series = {Journal of Superconductivity and Novel Magnetism}, volume = {28}, journal = {Journal of Superconductivity and Novel Magnetism}, number = {4}, issn = {1557-1939}, doi = {10.1007/s10948-014-2903-7}, pages = {1273 -- 1277}, abstract = {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.}, language = {en} } @misc{SeiboldUdinaCastellanietal., author = {Seibold, G{\"o}tz and Udina, Mattia and Castellani, Claudio and Benfatto, Lara}, title = {Third harmonic generation from collective modes in disordered superconductors}, series = {Physical Review B}, volume = {103}, journal = {Physical Review B}, number = {1}, doi = {10.1103/PhysRevB.103.014512}, pages = {19}, abstract = {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.}, language = {en} } @misc{SeiboldCastellaniLorenzana, author = {Seibold, G{\"o}tz and Castellani, Claudio and Lorenzana, Jos{\´e}}, title = {Adiabatic transition from a BCS superconductor to a Fermi liquid and phase dynamics}, series = {Physical Review B}, volume = {105}, journal = {Physical Review B}, number = {18}, issn = {2469-9969}, doi = {10.1103/PhysRevB.105.184513}, pages = {184513-1 -- 184513-14}, abstract = {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.}, language = {en} } @misc{CapraraDiCastroMirarchietal., author = {Caprara, Sergio and Di Castro, Carlo and Mirarchi, Giovanni and Seibold, G{\"o}tz and Grilli, Marco}, title = {Dissipation-driven strange metal behavior}, series = {Communications Physics}, journal = {Communications Physics}, number = {5}, issn = {2399-3650}, doi = {10.1038/s42005-021-00786-y}, pages = {1 -- 7}, abstract = {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.}, language = {en} } @misc{SeiboldArpaiaYingYingetal., author = {Seibold, G{\"o}tz and Arpaia, Riccardo and Ying Ying, Peng and Fumagalli, Roberto and Braicovich, Lucio and Di Castro, Carlo and Grilli, Marco and Ghiringhelli, Giacomo Claudio and Caprara, Sergio}, title = {Strange metal behaviour from charge density fluctuations in cuprates}, series = {Communications Physics}, volume = {4}, journal = {Communications Physics}, issn = {2399-3650}, doi = {10.1038/s42005-020-00505-z}, pages = {1 -- 6}, abstract = {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.}, language = {en} } @misc{SeiboldBenfattoCastellani, author = {Seibold, G{\"o}tz and Benfatto, Lara and Castellani, Claudio}, title = {Application of the Mattis-Bardeen theory in strongly disordered superconductors}, series = {Physical Review B}, volume = {96}, journal = {Physical Review B}, number = {14}, doi = {10.1103/PhysRevB.96.144507}, pages = {144507}, abstract = {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.}, language = {en} } @misc{NoatschkHofmannDabrowskietal., author = {Noatschk, Katharina and Hofmann, E. V. S. and Dabrowski, J. and Curson, N. J. and Schr{\"o}der, Thomas and Klesse, Wolfgang Matthias and Seibold, G{\"o}tz}, title = {Ge(001) surface reconstruction with Sn impurities}, series = {Surface Science}, volume = {713}, journal = {Surface Science}, doi = {10.1016/j.susc.2021.121912}, pages = {1 -- 8}, abstract = {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.}, language = {en} }