Observation of Quantum-Criticality-Class Crossover at the LaAlO_{3}/KTaO_{3} (111) Interface.

In the 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 lower T_{c} sample with weaker spin-orbit coupling (SOC) to the anomalous QGS in a higher T_{c} sample with stronger SOC. Moreover, owing to the remarkable SOC strength, the higher 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 Letter 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.