AC conductivity of a niobium thin film in a swept magnetic field

TL;DR

This study investigates the ac conductivity of a niobium superconducting thin film under a swept magnetic field, revealing vortex dynamics and dissipation behavior with a phenomenological model explaining key features.

Contribution

It introduces a phenomenological model that accurately describes the ac response and vortex behavior in a niobium thin film under swept magnetic fields.

Findings

Vortex generation rate is independent of dc field value.

Large plateau region of constant dissipation observed.

Model explains dependence on sweep rate, amplitude, frequency, and harmonics.

Abstract

We report the results of the measurement the ac conductivity of a Nb superconducting thin film in a swept dc magnetic field. In the mixed state the swept dc field creates vortices at the film surface which pass through the film and form the observed ac conductivity. Vortex rate generation does not depend on the value of the dc field and there is a large plateau-like region of dc magnetic fields where the dissipation is approximately constant. A proposed phenomenological model describes quite well the main features of the ac response in these fields including its dependency on the sweep rate, ac amplitude, frequency, and value of the second and third harmonics.