A Striped Electron Fluid on (111) KTaO$_3$

TL;DR

This paper models the electron behavior at the EuO/(111) KTaO$_3$ interface, revealing a magnetic stripe instability that explains observed transport anisotropy and suggesting a link to superconductivity.

Contribution

It introduces a minimal tight binding and $k ext{ extperiodcentered}p$ model capturing the magnetic stripe order and its effects on the 2DEG in EuO/KTaO$_3$.

Findings

Hexagonal Fermi surface with enhanced 2$k_F$ susceptibility.

Magnetic stripe instability leads to partial Fermi surface gapping.

Possible connection between stripe order and superconductivity.

Abstract

A recent study has revealed that the low carrier density electron gas (2DEG) induced at the interface of EuO and (111) KTaO$_3$ exhibits a broken symmetry phase with a strong in-plane anisotropy of the resistivity. We present a minimal tight binding model of this (111) 2DEG, including the large spin-orbit coupling from the Ta ions, which reveals a hexagonal Fermi surface with a highly enhanced 2$k_F$ electronic susceptibility. We argue that repulsive electronic interactions, together with a ferromagnetic EuO substrate, favor a magnetic stripe instability leading to a partially gapped Fermi surface. Such a stripe state, or its vestigial nematicity, could explain the observed transport anisotropy. We propose a $k\cdot p$ theory for the low energy $j=3/2$ states, which captures the key results from our tight-binding study, and further reveals the intertwined dipolar and octupolar modulations underlying this magnetic stripe order. We conclude by speculating on the relation of this stripe order to the superconductivity seen in this material.