@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 = {Intrinsic spin Hall effect in systems with striped spin-orbit coupling}, series = {epl : a letters journal exploring the frontiers of physics}, volume = {112}, journal = {epl : a letters journal exploring the frontiers of physics}, number = {1}, issn = {1286-4854}, doi = {http://dx.doi.org/10.1209/0295-5075/112/17004}, pages = {17004-p1 -- 17004-p6}, 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{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{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{CapatiCapraraDiCastroetal., author = {Capati, Matteo and Caprara, Sergio and Di Castro, Carlo and Grilli, Marco and Seibold, G{\"o}tz and Lorenzana, Jos{\´e}}, title = {Electronic polymers and soft-matter-like broken symmetries in underdoped cuprates}, series = {Nature Communications}, volume = {6}, journal = {Nature Communications}, issn = {2041-1723}, doi = {doi:10.1038/ncomms8691}, pages = {7691}, abstract = {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.}, language = {en} } @misc{CapraraGrilliDiCastroetal., author = {Caprara, Sergio and Grilli, Marco and Di Castro, Carlo and Seibold, G{\"o}tz}, title = {Pseudogap and (An)isotropic Scattering in the Fluctuating Charge-Density Wave Phase of Cuprates}, series = {Journal of Superconductivity and Novel Magnetism}, volume = {30}, journal = {Journal of Superconductivity and Novel Magnetism}, number = {1}, issn = {1557-1939}, doi = {10.1007/s10948-016-3775-9}, pages = {25 -- 30}, abstract = {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).}, language = {en} } @misc{WahlbergArpaiaSeiboldetal., author = {Wahlberg, Eric and Arpaia, Riccardo and Seibold, G{\"o}tz and Rossi, Matteo and Fumagalli, Roberto and Trabaldo, Edoardo and Brookes, Nicholas B. and Braicovich, Lucio and Caprara, Sergio and Lombardi, Floriana and Gran, Ulf and Ghiringhelli, Giacomo Claudio and Bauch, Thilo}, title = {Restored strange metal phase through suppression of charge density waves in underdoped YBa2Cu3O7-δ}, series = {Science}, volume = {373}, journal = {Science}, number = {6562}, doi = {10.1126/science.abc8372}, pages = {1506 -- 1510}, abstract = {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.}, 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} } @misc{SeiboldCapraraGrillietal., author = {Seibold, G{\"o}tz and Caprara, Sergio and Grilli, Marco and Raimondi, Roberto}, title = {Inhomogeneous Rashba spin-orbit coupling and intrinsic spin-Hall effect}, series = {Journal of Magnetism and Magnetic Materials}, volume = {440}, journal = {Journal of Magnetism and Magnetic Materials}, doi = {10.1016/j.jmmm.2016.12.066}, pages = {63 -- 65}, abstract = {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.}, 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{SeiboldCapraraGrillietal., author = {Seibold, G{\"o}tz and Caprara, Sergio and Grilli, Marco and Raimondi, Roberto}, title = {Non-equilibrium Spin Currents in Systems with Striped Rashba Spin-Orbit Coupling}, series = {Journal of Superconductivity and Novel Magnetism}, volume = {30}, journal = {Journal of Superconductivity and Novel Magnetism}, number = {1}, issn = {1557-1939}, doi = {10.1007/s10948-016-3774-x}, pages = {123 -- 128}, abstract = {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.}, 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{SeiboldBucheliCapraraetal., author = {Seibold, G{\"o}tz and Bucheli, Daniel and Caprara, Sergio and Grilli, Marco}, title = {Phase separation and long-wavelength charge instabilities in spin-orbit coupled systems}, series = {EPL Europhysics Letters}, volume = {109}, journal = {EPL Europhysics Letters}, number = {1}, issn = {1286-4854}, doi = {10.1209/0295-5075/109/17006}, pages = {17006}, abstract = {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.}, 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} } @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 = {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} }