Systematic study of disorder induced by neutron irradiation in MgB2 thin films

TL;DR

This study systematically investigates how neutron irradiation affects the structural, electronic, and superconducting properties of MgB2 thin films, revealing the suppression of superconductivity and high critical fields unaffected by disorder.

Contribution

It provides a comprehensive analysis of neutron-induced disorder in MgB2 thin films and introduces a model explaining the high critical fields independent of resistivity.

Findings

Superconductivity is suppressed with increasing neutron fluence.

Critical fields remain extremely high and are relatively unaffected by disorder at low fluences.

Residual resistivity increases significantly, indicating increased scattering.

Abstract

The effects of neutron irradiation on normal state and superconducting properties of epitaxial magnesium diboride thin films are studied up to fluences of 1020 cm-2. All the properties of the films change systematically upon irradiation. Critical temperature is suppressed and, at the highest fluence, no superconducting transition is observed down to 1.8 K. Residual resistivity progressively increases from 1 to 190 microohmcm; c axis expands and then saturates at the highest damage level. We discuss the mechanism of damage through the comparison with other damage procedures. The normal state magnetoresistivity of selected samples measured up to high fields (28 and 45T) allows to determine unambiguously the scattering rates in each band; the crossover between the clean and dirty limit in each sample can be monitored. This set of samples, with controlled amount of disorder, is suitable to study the puzzling problem of critical field in magnesium diboride thin films. The measured critical field values are extremely high (of the order of 50T in the parallel direction at low fluences) and turns out to be rather independent on the experimental resistivity, at least at low fluences. A simple model to explain this phenomenology is presented.