Zeeman driven superconductor insulator transition in strongly disordered MoC film. STM and transport studies in transverse magnetic field

TL;DR

This study investigates the superconductor-insulator transition in highly disordered MoC films under transverse magnetic fields, revealing dominant Zeeman effects and their impact on electronic states and transport properties.

Contribution

It demonstrates that Zeeman paramagnetic effects dominate over orbital effects in disordered MoC films, with detailed STM and transport evidence of their role in the transition.

Findings

Zeeman effects dominate over orbital coupling in the transition

High upper critical magnetic field with square root temperature dependence

Logarithmic anomaly in density of states at critical field

Abstract

Superconductor insulator transition in transverse magnetic field is studied in the highly disordered MoC film with the product of the Fermi momentum and the mean free path $k_F*l$ close to unity. Surprisingly, the Zeeman paramagnetic effects dominate over orbital coupling on both sides of the transition. In superconducting state it is evidenced by a high upper critical magnetic field $B_{c2}$, by its square root dependence on temperature, as well as by the Zeeman splitting of the quasiparticle density of states (DOS) measured by scanning tunneling microscopy. At $B_{c2}$ a logarithmic anomaly in DOS is observed. This anomaly is further enhanced in increasing magnetic field, which is explained by the Zeeman splitting of the Altshuler-Aronov DOS driving the system into a more insulating or resistive state. Spin dependent Altshuler-Aronov correction is also needed to explain the transport behavior above $B_{c2}$.