Interplay between superconductivity and magnetism in one-unit-cell LaAlO3 capped with SrTiO3

TL;DR

This study demonstrates that capping LaAlO3 with SrTiO3 enhances interface stability and reveals unconventional superconductivity with unique magnetic responses, providing a robust platform for exploring interplay between superconductivity and magnetism.

Contribution

It introduces a SrTiO3 capping method that overcomes thickness limitations and stabilizes the LaAlO3/SrTiO3 interface, enabling new insights into their superconducting and magnetic properties.

Findings

Enhanced interface stability and controllability with SrTiO3 capping.

Observation of unconventional superconductivity with increased critical current under magnetic field.

Reversed hysteresis in magnetoresistance indicating novel magnetic behavior.

Abstract

To form a conducting layer at the interface between the oxide insulators LaAlO3 and SrTiO3, the LaAlO3 layer on the SrTiO3 substrate must be at least four unit-cells-thick. The LaAlO3 SrTiO3 heterointerface thus formed exhibits various intriguing phenomena such as ferromagnetism and superconductivity. It has been widely studied for being a low-dimensional ferromagnetic oxide superconducting system with a strong gate-tunable spin-orbit interaction. However, its lack of stability and environmental susceptiveness have been an obstacle to its further experimental investigations and applications. Here, we demonstrate that capping the bilayer with SrTiO3 relieves this thickness limit, while enhancing the stability and controllability of the interface. In addition, the SrTiO3-capped LaAlO3 exhibits unconventional superconductivity; the critical current dramatically increases under a parallel magnetic field, and shows a reversed hysteresis contrary to the conventional hysteresis of magnetoresistance. Its superconducting energy gap of $\Delta \sim 1.31k_BT_c$ also deviates from conventional BCS-type superconductivity. The oxide trilayer could be a robust platform for studying the extraordinary interplay of superconductivity and ferromagnetism at the interface electron system between LaAlO3 and SrTiO3.