Magnetic Field Tuned Quantum Phase Transition in the Insulating Regime of Ultrathin Amorphous Bi Films

TL;DR

This study investigates a magnetic field-induced quantum phase transition in ultrathin amorphous Bi films, revealing a crossover between insulating states characterized by resistance peaks and Arrhenius behavior.

Contribution

It provides evidence of a magnetic field-tuned quantum phase transition between two insulating ground states in amorphous Bi films, with unique resistance and magnetoresistance behaviors.

Findings

Resistance peaks at specific magnetic fields.

Magnetoresistance isotherms cross at a well-defined field.

Activation energy and prefactor behaviors indicate quantum phase transition.

Abstract

A surprisingly strong variation of resistance with perpendicular magnetic field, and a peak in the resistance vs. field, R(B) has been found in insulating films of a sequence of homogeneous, quench-condensed films of amorphous Bi undergoing a thickness-tuned superconductor-insulator transition. Isotherms of magnetoresistance, rather than resistance, vs. field were found to cross at a well-defined magnetic field higher than the field corresponding to the peak in R(B). For all values of B, R(T) was found to obey an Arrhenius form. At the crossover magnetic field the prefactor became equal to the quantum resistance of electron pairs, h/4e^2, and the activation energy returned to its zero field value. These observations suggest that the crossover is the signature of a quantum phase transition between two distinct insulating ground states, tuned by magnetic field.