Super-hard Superconductivity

TL;DR

This paper investigates the magnetic response of Type-II superconductors in an extreme pinning limit, revealing a cascade of Meissner-like phases and a flux penetration model with implications for superconductor hardness.

Contribution

It introduces the concept of 'super-hard' superconductivity in highly disordered Nb and V wires, demonstrating a cascade of phases and validating an exponential flux penetration model.

Findings

Magnetization response shows cascade of Meissner-like phases.

Flux penetration depth fits exponential model J_c(B)=J_co exp(-B/B_o).

Implications for fundamental superconductor hardness discussed.

Abstract

We present a study of the magnetic response of Type-II superconductivity in the extreme pinning limit, where screening currents within an order of magnitude of the Ginzburg-Landau depairing critical current density develop upon the application of a magnetic field. We show that this "super-hard" limit is well approximated in highly disordered, cold drawn, Nb and V wires whose magnetization response is characterized by a cascade of Meissner-like phases, each terminated by a catastrophic collapse of the magnetization. Direct magneto-optic measurements of the flux penetration depth in the virgin magnetization branch are in excellent agreement with the exponential model in which J_c(B)=J_co exp(-B/B_o), where J_co~5x10^6 A/cm^2 for Nb. The implications for the fundamental limiting hardness of a superconductor are discussed.