Abstract
The ferroelectric degenerate semiconductor exhibits superconductivity with critical temperatures, , of up to 0.3 K for hole densities of order . When doped on the tin site with greater than 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 than for . By examining the effect of In dopant atoms on both and the temperature of the ferroelectric structural phase transition, , we show that phonon modes related to this transition are not responsible for this enhancement, and discuss a plausible candidate based on negative pairing associated with mixed valency on the indium impurity sites.
- Received 15 August 2008
DOI:https://doi.org/10.1103/PhysRevB.79.024520
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