Enhanced superconducting pairing interaction in indium-doped tin telluride

TL;DR

This study reveals that indium doping in SnTe enhances superconducting pairing interaction without significantly changing carrier density, with specific heat data indicating a stronger pairing for higher indium concentrations.

Contribution

It demonstrates that indium doping increases superconducting pairing strength in SnTe independently of carrier density changes, and rules out phonon modes related to ferroelectric transition as the cause.

Findings

Superconductivity increases up to 2 K with indium doping.

Stronger pairing interaction observed for x > x_c.

Phonon modes related to ferroelectric transition are not responsible.

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.