Non--Ginsburg-Landau Critical Current Behavior in MgCNi3

TL;DR

This study investigates the critical current behavior of MgCNi3 superconductors, revealing unconventional scaling laws and an anomalous temperature dependence of the London penetration depth, indicating an unusual superconducting ground state.

Contribution

It provides the first detailed transport critical current measurements of MgCNi3 microfibers, showing non-Ginsburg-Landau behavior and exponential field dependence, suggesting novel superconducting properties.

Findings

Critical current density follows a power law near Tc without Ginsburg-Landau crossover.

Extrapolated Jc(0) is significantly higher than magnetization estimates.

Critical current exhibits purely exponential decay with magnetic field.

Abstract

We present transport critical current measurements on microfibers consisting of a 80-nm thick layer of polycrystalline MgCNi3 synthesized directly onto 7-micron diameter carbon fibers. Near the transition temperature, Tc, the critical current density, Jc, is well described by the power law form [1-(T/T_c)^2)]^2, with no crossover to the Ginsburg-Landau exponent 1.5. We extrapolate Jc(0) ~ 4 x 10^7 A/cm^2, which is an order of magnitude greater than estimates obtained from magnetization measurements of polycrystalline powders. The field dependence is purely exponential Jc(T,H) = Jc(T) exp(-H/Ho) over the entire field range of 0 to 9 T. The unconventional scaling behavior of the critical current appears rooted in an anomalous temperature dependence of the London penetration depth, suggesting an unusual superconducting ground state in MgCNi3.