Experimental Study of the Inductance of Pinned Vortices in Superconducting YBa2Cu3O7-d Films

TL;DR

This study measures the inductance of pinned vortices in YBa2Cu3O7-d superconducting films, revealing how vortex pinning and thermal fluctuations influence complex resistivity at low temperatures and magnetic fields.

Contribution

It provides a detailed experimental analysis of vortex inductance and introduces a simple model incorporating thermal fluctuations to explain the observed resistivity behavior.

Findings

Inductive vortex resistivity inversely proportional to pinning force constant.

Weakening of pinning with magnetic field consistent with linear defect model.

Thermal fluctuations explain linear temperature dependence of resistivity below 15 K.

Abstract

Using a two-coil mutual inductance method, we have measured the complex resistivity, rho_v(T,Be), of pinned vortices in c-axis pulsed laser deposited YBa2Cu3O7-d films with magnetic field Be applied perpendicular to the film. At low frequencies, (<100 kHz), rho_v is inductive and is inversely proportional to the Labusch parameter, the average vortex pinning force constant, kappa_exp. The observed weakening of kappa_exp with Be is consistent with a simple model based on linear pinning defects. Adding classical thermal fluctuations to the model in a simple way describes the observed linear T dependence of rho_v, below ~15 K and provides reasonable values for the effective radius (.3 nm to >.8 nm) of the defects and the depth of the pinning potential. The success of this model implies that thermal supercurrent (phase) fluctuations have their full classical amplitude down to 5 K for frequencies below the characteristic depinning frequency. To date, no sufficient theory exists to explain the data between ~15 K and the vortex glass melting temperature.