Novel Emergent Phases in a Two-Dimensional Superconductor

TL;DR

This study uncovers complex emergent phases in a 2D superconductor heterostructure, revealing unexpected suppression of quantum Griffiths phases and challenging existing theories of quantum criticality.

Contribution

It reports the discovery of novel emergent phases and phenomena in a 2D superconductor, including suppression of QGP and deviations from infinite-randomness criticality predictions.

Findings

Observation of a rich phase diagram with superconducting and magnetic phases.

Suppression of quantum Griffiths phase below a crossover temperature.

Destruction of the superconducting quantum critical point at low temperatures.

Abstract

In this letter, we report our observation of an extraordinarily rich phase diagram of a LaScO$_3$/SrTiO$_3$ heterostructure. Close to the superconducting transition temperature, the system hosts a superconducting critical point of the Infinite-randomness type characterized by an effective dynamical exponent $\nu z$ that diverges logarithmically. At lower temperatures, we find the emergence of a magnetic field-tuned metallic phase that co-exists with a quantum Griffiths phase (QGP). Our study reveals a previously unobserved phenomenon in 2D superconductors -- an unanticipated suppression of the QGP below a crossover temperature in this system. This concealment is accompanied by the destruction of the superconducting quantum critical point signaled by a power-law divergence (in temperature) of the effective dynamical exponent. These observations are entirely at odds with the predictions of the infinite-randomness scenario and challenge the very concept of a vanishing energy scale associated with a quantum critical point. We develop and discuss possible scenarios like smearing of the phase transition that could plausibly explain our observations. Our findings challenge the notion that QGP is the ultimate ground state in two-dimensional superconductors.