rf-studies of vortex dynamics in isotropic type-II superconductors

TL;DR

This study investigates vortex dynamics in isotropic type-II superconductors by measuring surface impedance over a broad frequency range, revealing a broad depinning crossover and size effects that challenge classical models.

Contribution

It introduces a two-mode model of vortex dynamics that explains the complex spectrum of apparent penetration depth, accounting for surface pinning and bulk vortex flow.

Findings

Depinning crossover is broader than classical theories predict.

Size effects invalidate the single penetration depth interpretation.

A two-mode model accurately describes vortex dynamics spectrum.

Abstract

We have measured the surface impedance of thick superconductors in the mixed state over a broad 2 kHz - 20 MHz frequency range. The depinning cross-over is observed; but it is much broader than expected from classical theories of pinning. A striking result is the existence of size effects which invalidate the common interpretation of the low-frequency surface inductance in terms of a single penetration depth. Instead, a two-mode description of vortex dynamics, assuming free vortex flow in the bulk and surface pinning, accounts quantitatively for the spectrum of the complex apparent penetration depth.