Critical flux pinning and enhanced upper-critical-field in magnesium diboride films

TL;DR

This study investigates flux pinning and the upper-critical-field in magnesium diboride films, revealing significant enhancements due to intrinsic disorder and three-dimensionality, with implications for superconductor performance.

Contribution

It provides new insights into flux pinning mechanisms and critical field enhancements in MgB2 films through comprehensive pulsed transport measurements.

Findings

Six-fold increase in $H_{c2}$ due to disorder and dimensionality

Depinning current density $j_c$ approaches depairing current $j_d$

Non-linear current-voltage response with no Ohmic flux-flow regime

Abstract

We have conducted pulsed transport measurements on c-axis oriented magnesium diboride films over the entire relevant ranges of magnetic field $0 \alt H \alt H_{c2}$ (where \hcu is the upper critical field) and current density $0 \alt j \alt j_{d}$ (where $j_{d}$ is the depairing current density). The intrinsic disorder of the films combined with the large coherence length and three-dimensionality, compared to cuprate superconductors, results in a six-fold enhancement of $H_{c2}$ and raises the depinning current density $j_{c}$ to within an order of magnitude of $j_{d}$. The current-voltage response is highly non-linear at all fields, resulting from a combination of depinning and pair-breaking, and has no trace of an Ohmic free-flux-flow regime. Keywords: pair, breaking, depairing, superconductor, superconductivity, flux, fluxon, vortex, mgb2