Heat capacity ofV3Xcompounds and the relationship betweenTcand anharmonicity

Abstract

The heat capacities of ${\mathrm{V}}_3$Si, ${\mathrm{V}}_3$Ga, ${\mathrm{V}}_3$Sn, and ${\mathrm{V}}_3$ ${\mathrm{Sn}}_{0.5}$ ${\mathrm{Ga}}_{0.5}$ were measured between 2 and 400°K. The high-$T_c$ compounds ${\mathrm{V}}_3$Ga and ${\mathrm{V}}_3$Si have smaller high-temperature heat capacities than the two lower-$T_c$ materials. Given the magnitudes of the measured low-temperature heat capacities, this observation can only result from unusually large anharmonicity of the higher-$T_c$ compounds. A phenomenological model is proposed that semiquantitatively relates the electron-phonon mass enhancement, and hence $T_c$, to the high-temperature anharmonic heat capacity observed in these materials. The model assumes a temperature-dependent screening caused by sharp structure in the electronic density of states, which renormalizes the bare phonon-mode frequencies.