Enhanced superconducting pairing interaction in indium-doped tin telluride

Abstract

The ferroelectric degenerate semiconductor Sn${}_{1-\delta }$Te exhibits superconductivity with critical temperatures, $T_c$, of up to 0.3 K for hole densities of order 10${}^{21}$ cm${}^{-3}$. When doped on the tin site with greater than $x_c$ $=1.7(3)$ indium atoms, however, superconductivity is observed up to 2 K, though the carrier density does not change significantly. We present specific heat data showing that a stronger pairing interaction is present for $x>x_c$ than for $x<x_c$. By examining the effect of In dopant atoms on both $T_c$ and the temperature of the ferroelectric structural phase transition, $T_{SPT}$, we show that phonon modes related to this transition are not responsible for this $T_c$ enhancement, and discuss a plausible candidate based on the unique properties of the indium impurities.

7 pages