Effects of disorder on high-temperature superconductivity in cubic MoN

Abstract

Three types of calculations have been used to help us understand the effects of disorder, alloying, and nonstoichiometry on the superconducting transition temperature ${T}_{c}$ of MoN, predicted to have ${T}_{c}$=29 K in the ideal B1 structure. (1) Simple disorder broadening indicates a strong lowering of ${T}_{c}$ which, however, does not account for the very low ${T}_{c}$'s measured in ${\mathrm{MoN}}_{\mathrm{x}}$ thin films. (2) Rigid-band calculations of the alloy system ${\mathrm{Nb}}_{1\mathrm{\ensuremath{-}}\mathrm{y}}$${\mathrm{Mo}}_{\mathrm{y}}$${\mathrm{N}}_{1.0}$ reproduce the measured trend in ${T}_{c}$ for y\ensuremath{\le}0.5. (3) Taking explicit account of metal ${t}_{2g}$--N p bonding in a coherent-potential-approximation model of ${\mathrm{MoN}}_{\mathrm{x}}$ leads to a semiquantitative understanding of the low measured ${T}_{c}$ values in films in terms of N vacancies, despite the nominal stoichiometry in some of the films.