@misc{BovenziCapraraGrillietal., author = {Bovenzi, Nicandro and Caprara, Sergio and Grilli, Marco and Raimondi, Roberto and Scopigno, Niccol{\`o} and Seibold, G{\"o}tz}, title = {Density inhomogeneities and Rashba spin-orbit coupling interplay in oxide interfaces}, series = {Journal of Physics and Chemistry of Solids}, journal = {Journal of Physics and Chemistry of Solids}, issn = {0022-3697}, pages = {12}, abstract = {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.}, language = {en} } @misc{SeiboldCapraraGrillietal., author = {Seibold, G{\"o}tz and Caprara, Sergio and Grilli, Marco and Raimondi, Roberto}, title = {Theory of the Spin Galvanic Effect at Oxide Interfaces}, series = {Physical Review Letters}, volume = {119}, journal = {Physical Review Letters}, number = {25}, issn = {1092-0145}, doi = {10.1103/PhysRevLett.119.256801}, abstract = {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.}, language = {en} } @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{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{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{MirarchiSeiboldDiCastroetal., author = {Mirarchi, Giovanni and Seibold, G{\"o}tz and Di Castro, Carlo and Grilli, Marco and Caprara, Sergio}, title = {The Strange-Metal Behavior of Cuprates}, series = {Condensed Matter}, volume = {7}, journal = {Condensed Matter}, number = {1}, issn = {2410-3896}, doi = {10.3390/condmat7010029}, pages = {1 -- 17}, abstract = {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.}, language = {en} } @misc{MirarchiGrilliSeiboldetal., author = {Mirarchi, Giovanni and Grilli, Marco and Seibold, G{\"o}tz and Caprara, Sergio}, title = {The Shrinking Fermi Liquid Scenario for Strange-Metal Behavior from Overdamped Optical Phonons}, series = {Condensed Matter}, volume = {9}, journal = {Condensed Matter}, number = {1}, issn = {2410-3896}, doi = {10.3390/condmat9010014}, pages = {1 -- 13}, abstract = {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.}, language = {en} } @misc{CapraraDiCastroMirarchietal., author = {Caprara, Sergio and Di Castro, Carlo and Mirarchi, Giovanni and Seibold, G{\"o}tz and Grilli, Marco}, title = {The shrinking fermi liquid scenario for cuprates under the scrutiny of optical conductivity measurements}, series = {Materials}, volume = {17}, journal = {Materials}, number = {23}, publisher = {MDPI AG}, issn = {1996-1944}, doi = {10.3390/ma17235849}, abstract = {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.}, language = {en} } @misc{MirarchiArpaiaWahlbergetal., author = {Mirarchi, Giovanni and Arpaia, Riccardo and Wahlberg, Eric and Bauch, Thilo and Kalaboukhov, Alexei and Caprara, Sergio and Di Castro, Carlo and Grilli, Marco and Lombardi, Floriana and Seibold, G{\"o}tz}, title = {Tuning the ground state of cuprate superconducting thin films by nanofaceted substrates}, series = {Communications Materials}, journal = {Communications Materials}, number = {5}, doi = {10.1038/s43246-024-00582-5}, pages = {1 -- 6}, abstract = {Anisotropic transport properties have been assessed in a number of cuprate superconductors, providing evidence for a nematic state. We have recently shown that in ultra-thin YBa2Cu3O7-δ films, where nematicity is induced via strain engineering, there is a suppression of charge density wave scattering along the orthorhombic a-axis and a concomitant enhancement of strange metal behavior along the b-axis. Here we develop a microscopic model, that is based on the strong interaction between the substrate facets and the thin film, to account for the unconventional phenomenology. Based on the atomic force microscopy imaging of the substrates' surface, the model is able to predict the absence (presence) of nematicity and the resulting transport properties in films grown on SrTiO3 (MgO) substrates. Our result paves the way to new tuning capabilities of the ground state of high-temperature superconductors by substrate engineering.}, language = {en} } @misc{GrilliDiCastroMirarchietal., author = {Grilli, Marco and Di Castro, Carlo and Mirarchi, Giovanni and Seibold, G{\"o}tz and Caprara, Sergio}, title = {Dissipative Quantum Criticality as a Source of Strange Metal Behavior}, series = {Symmetry}, volume = {15}, journal = {Symmetry}, number = {3}, issn = {2073-8994}, doi = {10.3390/sym15030569}, abstract = {The strange metal behavior, usually characterized by a linear-in-temperature (T) resistivity, is a still unsolved mystery in solid-state physics. It is often associated with the proximity to a quantum critical point (a second order transition at temperature T=0, leading to a broken symmetry phase) focusing on the related divergent order parameter correlation length. Here, we propose a paradigmatic shift, focusing on a divergent characteristic time scale due to a divergent dissipation acting on the fluctuating critical modes while their correlation length stays finite. To achieve a divergent dissipation, we propose a mechanism based on the coupling between a local order parameter fluctuation and electron density diffusive modes that accounts both for the linear-in-T resistivity and for the logarithmic specific heat versus temperature ratio CV/T∼log(1/T), down to low temperatures.}, language = {en} }