Phase diagrams of voltage-gated oxide interfaces with strong Rashba coupling

TL;DR

This paper models the two-dimensional electron gas at oxide interfaces with Rashba spin-orbit coupling, revealing phase separation instabilities and quantum critical points influenced by temperature, magnetic fields, and gating potential.

Contribution

It introduces a comprehensive model incorporating electric field-dependent Rashba coupling and analyzes phase separation and quantum criticality at oxide interfaces.

Findings

Phase separation instability occurs at realistic parameters.

Phase diagrams show a phase separation dome affected by temperature and magnetic fields.

Quantum critical points emerge where phase separation vanishes.

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 which 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.