Interband and intraband effects in the upper critical field of disorderedMgB2

Abstract

In this work the superconducting properties of disordered ${\text{MgB}}_{2}$ in applied magnetic field are studied within the ${\ensuremath{\lambda}}^{\ensuremath{\theta}\ensuremath{\theta}}$ model, by taking into account the presence of both interband and intraband scattering with impurities. This approach allows to extract the suppression of the critical temperature ${T}_{c}$ and the enhancement of the upper critical field ${H}_{{c}_{2}}$, as a consequence of the introduction of impurities in the samples. We analyze the dependence of ${H}_{{c}_{2}}$ on temperature, anisotropy of the electronic structure, and intraband $\ensuremath{\sigma}$ and $\ensuremath{\pi}$ band scattering rates. Comparing our numerical calculations with experimental data on irradiated samples, we find that irradiation defects mainly affect the mobility of $\ensuremath{\sigma}$ carriers. These results rationalize why the ${H}_{{c}_{2}}$ anisotropy of irradiated samples is quickly reduced with increasing doses and full suppression of superconductivity occurs at rather low-resistivity values. Moreover, our calculations point out that disorder in the $\ensuremath{\pi}$ bands affects only weakly the coupling constants and thus it could yield a significant enhancement of ${H}_{{c}_{2}}$ without severe suppression of ${T}_{c}$.