Influence of In-induced resonant level on the normal-state and superconducting properties of Sn1.03Te

Abstract

Normal-state transport properties (2--300 K) of the polycrystalline series ${\mathrm{Sn}}_{1.03\ensuremath{-}\ensuremath{\delta}\ensuremath{-}x}{\mathrm{In}}_{x}\mathrm{Te} (0\ensuremath{\le}x\ensuremath{\le}0.07$; $\ensuremath{\delta}\ensuremath{\le}0.0025$) were investigated by means of electrical resistivity, thermopower, Hall effect, and thermal conductivity measurements. The distortion of the valence-band structure by the In-induced resonant level (RL) has a profound influence on the evolution of the normal-state properties with $x$ and on the emergence of superconductivity evidenced by specific-heat measurements down to 0.35 K. In addition to a nearly 40-fold increase in the residual electrical resistivity ${\ensuremath{\rho}}_{0}$ on going from $x=0.0$ to 0.05, the thermopower $\ensuremath{\alpha}$ shows a nonlinear, complex behavior as a function of both temperature and $x$. While Hall measurements indicate a dominant holelike response across the entire composition and temperature ranges, $\ensuremath{\alpha}$ changes sign below about 100 K and remains negative down to 5 K for $0.0015\ensuremath{\le}x\ensuremath{\le}0.0045$. Additional measurements under magnetic fields ${\ensuremath{\mu}}_{0}H$ of up to 14 T further shows that $\ensuremath{\alpha}({\ensuremath{\mu}}_{0}H)$ gradually shifts towards positive values, suggestive of a dominant holelike contribution to $\ensuremath{\alpha}$. Superconductivity emerges for $x=0.02$ at a critical temperature ${T}_{\mathrm{c}}=0.67$ K, with ${T}_{\mathrm{c}}$ increasing with $x$ to reach 1.73 K for $x=0.07$. The variations in the superconducting parameters with $x$, notably the specific-heat jump at ${T}_{\mathrm{c}}$, confirm the results reported in prior studies and suggests a nontrivial role of the RL on the electron-phonon coupling strength. The striking similarities between this series and the canonical resonant system ${\mathrm{Pb}}_{1\ensuremath{-}x}{\mathrm{Tl}}_{x}\mathrm{Te}$ provide an excellent experimental opportunity to gain a deeper understanding of the close interplay between resonant level, anomalous transport properties, and superconductivity.