Imaging pinning and expulsion of individual superconducting vortices in amorphous MoSi thin films

TL;DR

This study employs a scanning SQUID to image and analyze individual vortices in amorphous MoSi thin films, revealing vortex behavior, pinning, and flux expulsion, which are vital for optimizing superconducting devices.

Contribution

It provides the first detailed imaging and quantification of vortex pinning and expulsion in amorphous MoSi films using a scanning SQUID.

Findings

Vortices follow the Pearl model in thin films.

Quantified vortex pinning and flux expulsion.

Measured Pearl length and penetration depth at 4.2 K.

Abstract

We use a scanning nanometer-scale superconducting quantum interference device (SQUID) to image individual vortices in amorphous superconducting MoSi thin films. Spatially resolved measurements of the magnetic field generated by both vortices and Meissner screening satisfy the Pearl model for vortices in thin films and yield values for the Pearl length and bulk penetration depth at 4.2 K. Flux pinning is observed and quantified through measurements of vortex motion driven by both applied currents and thermal activation. The effects of pinning are also observed in metastable vortex configurations, which form as the applied magnetic field is reduced and magnetic flux is expelled from the film. Understanding and controlling vortex dynamics in amorphous thin films is crucial for optimizing devices such as superconducting nanowire single photon detectors (SNSPDs), the most efficient of which are made from MoSi, WSi, and MoGe.