Infinite-randomness fixed point of the quantum superconductor-metal transitions in amorphous thin films

TL;DR

This paper demonstrates that amorphous indium oxide films undergoing a superconductor-metal transition exhibit an infinite randomness fixed point, with resistance data collapsing under an activated scaling form, revealing exotic quantum critical behavior.

Contribution

It provides experimental evidence for an infinite randomness fixed point in superconductor-metal transitions in amorphous films, supported by resistance scaling analysis.

Findings

Resistance obeys activated scaling near the transition

Data collapse supports infinite randomness fixed point

Exotic quantum critical behavior observed in films

Abstract

The magnetic-field-tuned quantum superconductor-insulator transitions of disordered amorphous indium oxide films are a paradigm in the study of quantum phase transitions, and exhibit power-law scaling behavior. For superconducting indium oxide films with low disorder, such as the ones reported on here, the high-field state appears to be a quantum-corrected metal. Resistance data across the superconductor-metal transition in these films are shown here to obey an activated scaling form appropriate to a quantum phase transition controlled by an infinite randomness fixed point in the universality class of the random transverse-field Ising model. Collapse of the field-dependent resistance vs. temperature data is obtained using an activated scaling form appropriate to this universality class, using values determined through a modified form of power-law scaling analysis. This exotic behavior of films exhibiting a superconductor-metal transition is caused by the dissipative dynamics of superconducting rare regions immersed in a metallic matrix, as predicted by a recent renormalization group theory. The smeared crossing points of isotherms observed are due to corrections to scaling which are expected near an infinite randomness critical point, where the inverse disorder strength acts as an irrelevant scaling variable.