Enhancement of the high-magnetic field critical current density of superconducting MgB2 by proton irradiation

Magnesium diboride, MgB2, has a relatively high superconducting transition temperature(1), placing it between the families of low- and high-temperatur e (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhind ered by grain boundaries(2,3), making it potentially attractive for technol ogical applications in the temperature range 20-30 K. But in the bulk mater ial, the critical current density (J(c)) drops rapidly with increasing magn etic field strength(4). The magnitude and field dependence of the critical current are related to the presence of structural defects that can 'pin' th e quantized magnetic vortices that permeate the material, and a lack of nat ural defects in MgB2 may be responsible for the rapid decline of J(c) with increasing field strength(3). Here we show that modest levels of atomic dis order induced by proton irradiation enhance the pinning of vortices, thereb y significantly increasing J(c) at high field strengths. We anticipate that either chemical doping or mechanical processing should generate similar le vels of disorder, and so achieve performance that is technologically attrac tive in an economically viable way.