Specific heat of MgB_2 after irradiation

TL;DR

This study investigates how irradiation-induced disorder affects the superconducting gaps and critical fields of MgB_2, revealing gap averaging and significant increases in upper critical field without major T_c loss.

Contribution

It provides new insights into how neutron irradiation modifies the superconducting properties and critical fields of MgB_2, with practical implications for enhancing superconductor performance.

Findings

Irradiation suppresses T_c and averages the two superconducting gaps.

A suitable irradiation increases dH_{c2}/dT at T_c significantly.

Post-irradiation, the upper critical field exceeds 28 T at 0 K.

Abstract

We studied the effect of disorder on the superconducting properties of polycrystalline MgB_2 by specific-heat measurements. In the pristine state, these measurements give a bulk confirmation of the presence of two superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal weights. The scattering introduced by irradiation suppresses T_c and tends to average the two gaps although less than predicted by theory. We also found that by a suitable irradiation process by fast neutrons, a substantial bulk increase of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few degrees in T_c. The upper critical field of the sample after irradiation exceeds 28 T at T goes to 0 K.