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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.
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.
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.
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.
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.
On the Evaluation of the Spin Galvanic Effect in Lattice Models with Rashba Spin-Orbit Coupling
(2018)
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.