Magnetic field-induced quantum superconductor-insulator transition in $Nb_{0.15}Si_{0.85}$

TL;DR

This paper investigates how magnetic fields induce superconductor-insulator transitions in amorphous NbSi films, revealing different quantum and classical behaviors depending on field orientation.

Contribution

It identifies a clear signature of quantum superconductor-insulator transitions and shows the transition nature varies with magnetic field orientation.

Findings

Perpendicular field induces quantum fluctuations and possibly a Bose insulator.

Parallel field causes classical transition via Cooper pair breaking.

Critical magnetic field exhibits a kink in temperature profile as a signature.

Abstract

A study of magnetic-field tuned superconductor-insulator transitions in amorphous $Nb_{0.15}Si_{0.85}$ thin films shows that quantum superconductor-insulator transitions are characterized by an unambiguous signature -- a kink in the temperature profile of the critical magnetic field. Using this criterion, we show that the nature of the magnetic-field tuned superconductor-insulator transition depends on the orientation of the field with respect to the film. For perpendicular magnetic field, the transition is controlled by quantum fluctuations with indications for the existence of a Bose insulator; while for parallel magnetic field, the transition is classical, driven by the breaking of Cooper pairs at the temperature dependent critical field $H_{c2}$.