Dual Universality and Unconventional Phase Diagram of a Clean 2D Superconductor with Tunable Disorders

TL;DR

This study investigates quantum phase transitions in a clean 2D superconductor, MoS2, revealing universal scaling behaviors and the conditions for Bose metal states versus localized phases as disorder varies.

Contribution

It demonstrates two disorder-independent universal scalings in a clean 2D superconductor and clarifies the role of disorder in stabilizing different quantum phases.

Findings

Universal power-law scaling for metallic states

Activated dynamical scaling in quantum Griffiths transitions

Bose metal state emerges only after reaching a critical level of cleanness

Abstract

Weakly disordered two-dimensional (2D) superconductors can host richer quantum phase transitions than their highly-disordered counterparts. This is due to the insertion of a metallic state in the transition between a superconductor and an insulator. Disorders were predicted to show profound influences on the boundaries surrounding this intermediate metallic phase, affecting the existence of a metallic ground state called Bose metal and the dynamic processes in a quantum Griffiths state. Here we present a study on quantum phase transitions of a clean 2D superconductor, MoS2, under a perpendicular magnetic field as a function of disorder strength that is tuned electrostatically. We found two universal scaling behaviors independent of disorders: a power-law scaling applies for all metallic states, and an activated dynamical scaling characterizes transitions between quantum Griffiths state and weakly localized metal. A study over a range of disorder states in this unexplored clear regime suggests that a Bose metal ground state is expected only after reaching a critical cleanness. Whereas, stronger disorder stabilizes a true 2D superconductivity and enhances the quantum Griffiths phase.