Specific-heat measurements in superconducting indium-thallium alloys and the pseudopotential form factor

Abstract

Normal-state specific heats between 1 and 4.4 K and superconducting transition temperatures of pure indium and In-Tl alloys have been measured. Excellent agreement with previous results was found. ${N}_{\mathrm{BS}}(0)$ was extracted using our $\ensuremath{\gamma}$ values and Dynes's $\ensuremath{\lambda}$ values and shows a large variation. The measured variation of $\ensuremath{\lambda}〈{\ensuremath{\omega}}^{2}〉$ was also obtained from Dynes's results and found to be nearly linear in spite of the large variation of ${N}_{\mathrm{BS}}(0)$. This is shown to be a consequence of the fact that the ratio of the calculated average screened pseudopotential form factor to electron density of states, $\frac{〈{v}_{s}^{2}〉}{{N}_{\mathrm{BS}}(0)}$, is nearly constant across the alloy series for each element. No anomaly was found in the specific heat of ${\mathrm{In}}_{0.69}$${\mathrm{Tl}}_{0.31}$ at the expected martensitic transition temperature.