Magnetoresistance in the superconducting state at the (111) LaAlO$_3$/SrTiO$_3$ interface

TL;DR

This study investigates the magnetoresistance of (111) LaAlO$_3$/SrTiO$_3$ interfaces, revealing anisotropic behavior in the superconducting state that suggests the presence of unconventional superconductivity linked to the unique crystal orientation.

Contribution

First measurement of magnetoresistance in (111) LAO/STO heterostructures showing anisotropic effects indicative of unconventional superconductivity.

Findings

Magnetoresistance is hysteretic, indicating coexistence of magnetism and superconductivity.

Magnetoresistance exhibits unexpected anisotropy in the superconducting state.

Results suggest (111) LAO/STO may host unconventional superconducting pairing states.

Abstract

Condensed matter systems that simultaneously exhibit superconductivity and ferromagnetism are rare due the antagonistic relationship between conventional spin-singlet superconductivity and ferromagnetic order. In materials in which superconductivity and magnetic order is known to coexist (such as some heavy-fermion materials), the superconductivity is thought to be of an unconventional nature. Recently, the conducting gas that lives at the interface between the perovskite band insulators LaAlO$_3$ (LAO) and SrTiO$_3$ (STO) has also been shown to host both superconductivity and magnetism. Most previous research has focused on LAO/STO samples in which the interface is in the (001) crystal plane. Relatively little work has focused on the (111) crystal orientation, which has hexagonal symmetry at the interface, and has been predicted to have potentially interesting topological properties, including unconventional superconducting pairing states. Here we report measurements of the magnetoresistance of (111) LAO/STO heterostructures at temperatures at which they are also superconducting. As with the (001) structures, the magnetoresistance is hysteretic, indicating the coexistence of magnetism and superconductivity, but in addition, we find that this magnetoresistance is anisotropic. Such an anisotropic response is completely unexpected in the superconducting state, and suggests that (111) LAO/STO heterostructures may support unconventional superconductivity.