Observation of Quantum-Criticality-Class Crossover at the LaAlO$_3$/KTaO$_3$ (111) Interface

TL;DR

This study observes different quantum criticality classes at the LaAlO3/KTaO3 (111) interface, revealing how spin-orbit coupling influences quantum fluctuations and phase transitions in 2D superconductors.

Contribution

It reports the first observation of a switch between normal and anomalous quantum Griffiths singularities driven by spin-orbit coupling in the same system.

Findings

Normal QGS in low Tc sample with weaker SOC

Anomalous QGS in high Tc sample with stronger SOC

Enhanced quantum fluctuations near BKT transition temperature

Abstract

In two-dimensional (2D) limit, the quantum fluctuation is significantly enhanced which could induce a quantum phase transition. Investigating the quantum criticality is an effective approach to elucidate the underlying physics of 2D superconductivity. Here we report the observation of different universality classes of quantum criticality at the superconducting LaAlO$_3$/KTaO$_3$ (111) interface, i.e. the normal quantum Griffiths singularity (QGS) and the anomalous QGS. The switch of the quantum criticality class is observed from the normal QGS in a low $T_c$ sample with weaker spin-orbit coupling (SOC) to the anomalous QGS in a high $T_c$ sample with stronger SOC. Moreover, owing to the remarkable SOC strength, the high $T_c$ sample exhibits an unprecedentedly enhanced quantum fluctuation at an unusually elevated temperature approaching the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_{BKT}$. This work provides comprehensive recognition of the different quantum criticality classes in the same superconducting LaAlO$_3$/KTaO$_3$ (111) system, which deepens the understanding of the superconducting mechanism of interfacial superconductors.