Campbell Penetration Depth of a Superconductor in the Critical State

TL;DR

This study measures how the magnetic penetration depth in a superconductor varies with supercurrent and magnetic history, revealing hysteresis linked to vortex pinning effects in high-temperature superconductors.

Contribution

It introduces a detailed analysis of the Campbell penetration depth's dependence on supercurrent and hysteresis in cuprate and organic superconductors.

Findings

Penetration depth shows strong hysteresis below 25 K in Bi2Sr2CaCu2O8.

Hysteresis is attributed to vortex position shifts within pinning wells.

Similar effects observed in other cuprates and organic superconductors.

Abstract

The magnetic penetration depth $\lambda(T,H,j)$ was measured in the presence of a slowly relaxing supercurrent, $j$. In single crystal $\mathrm{Bi_2Sr_2CaCu_2O_8}$ below approximately 25 K, $\lambda(T,H,j)$ is strongly hysteretic. We propose that the irreversibility arises from a shift of the vortex position within its pinning well as $j$ changes. The Campbell length depends upon the ratio $j/j_{c}$ where $j_{c}$ is the critical current defined through the Labusch parameter. Similar effects were observed in other cuprates and in an organic superconductor.