Thickness dependence of critical currents in thin superconductors

TL;DR

This paper investigates how the critical current density in thin superconducting films depends on thickness, proposing a model based on vortex pinning and thermal fluctuations, and discusses experimental approaches to distinguish underlying mechanisms.

Contribution

It introduces a theoretical model for the thickness dependence of J_c in thin superconductors and suggests experimental methods to identify dominant factors.

Findings

J_c scales as (1/√d)exp[-(d_m/d)^{1/2}] at low fields for d < pinning length

Model explains observed J_c dependence in YBa2Cu3O7 films under 2 μm thickness

Proposes measurements in strong fields to differentiate pinning effects from microstructural changes

Abstract

Mechanisms of vortex dynamics and pinning and self-field effects which could account for the thickness dependence of the critical current density J_c of superconducting films are addressed. It is shown that at low magnetic fields B, the 2D single-vortex pinning and thermal fluctuations yield J_c proportional to (1/sqrt{d})exp[-(d_m/d)^{1/2}], if the film thickness d is smaller than the pinning correlation length along B. The model describes the dependence of J_c on d observed on YBa_2Cu_3O_7 coated conductors for d < 2(mu)m. Measurements of J_c(d) in strong magnetic fields are proposed to probe whether the dependence of J_c on d is mostly determined by the 2D pinning or changes in the material microstructure as the film gets thicker.