Depinning transition in type-II superconductors

TL;DR

This paper investigates the depinning transition in type-II superconductors by measuring surface impedance over a range of frequencies, revealing a new boundary-condition-driven model that aligns well with experimental data.

Contribution

It introduces a novel model emphasizing boundary conditions over classical vortex pinning theories, explaining the ac response in superconductors.

Findings

Universal law for Z(f) matches experimental data

Boundary conditions dominate vortex response

Model applies to YBaCuO films

Abstract

The surface impedance Z(f) of conventional isotropic materials has been carefully measured for frequencies f ranging from 1 kHz to 3 MHz, allowing a detailed investigation of the depinning transition. Our results exhibit the irrelevance of classical ideas to the dynamics of vortex pinning. We propose a new picture, where the linear ac response is entirely governed by disordered boundary conditions of a rough surface, whereas in the bulk vortices respond freely. The universal law for Z(f) thus predicted is in remarkable agreement with experiment, and tentatively applies to microwave data in YBaCuO films.