Superconducting quantum phase transitions tuned by magnetic impurity and magnetic field in ultrathin a-Pb films

TL;DR

This study investigates how superconducting quantum phase transitions in ultrathin a-Pb films are influenced by disorder, magnetic impurities, and magnetic fields, revealing different natures of these transitions and complex phase behaviors.

Contribution

It provides a comparative analysis of disorder, magnetic impurity, and magnetic field effects on superconducting transitions, highlighting the fermionic and bosonic characteristics of these processes.

Findings

Magnetic impurity suppresses critical temperature and induces a weakly insulating state.

Disorder-induced transition closely resembles impurity-tuned transition, both fermionic.

Magnetic field induces a potentially bosonic transition with mesoscale phase separation.

Abstract

Superconducting quantum phase transitions tuned by disorder (d), paramagnetic impurity (MI) and perpendicular magnetic field (B) have been studied in homogeneously disordered ultrathin a-Pb films. The MI-tuned transition is characterized by progressive suppression of the critical temperature to zero and a continuous transition to a weakly insulating normal state with increasing MI density. In all important aspects, the d-tuned transition closely resembles the MI-tuned transition and both appear to be fermionic in nature. The B-tuned transition is qualitatively different and probably bosonic. In the critical region it exhibits transport behavior that suggests a B-induced mesoscale phase separation and presence of Cooper pairing in the insulating state.