Research: Negative-U Superconductivity

High-Tc has left us with a series of unanswered questions, and developing model systems to address some of these issues is an important task. One particular question that we are currently addressing is whether charge-transfer layers play a totally passive role in achieving the highest Tc values. Negative-U interactions due to heavy ions in these layers could possibly enhance Tc, but the cuprates are very complex materials to investigate such an effect. PbTe lightly doped with Tl, and more recently SnTe doped with In, provide simpler model systems to explore the possibility of pairing interactions due to the action of valence-skipping elements.
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Fisher Research Group
Geballe Laboratory for Advanced Materials
Dept. of Applied Physics
Stanford University
CA 94305-4045
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