Superconductivity at the highest transition temperature of 8.1 K in a simple cubic Au_xSb_1-x-yTey alloy system synthesized under high pressure

Abstract

We have investigated superconductivity and structure in a gold–antimony–tellurium ternary alloy system (Au_xSb_1-x-yTey) synthesized under high pressure. We found that Au_0.125Sb_0.75Te_0.125 and AuSb₆Te when crystallized in simple cubic structures (α-Po type), which are reported to be semiconductors above 20 K, are superconductors with a transition temperature (T_c) of 6.7 K. The structure and T_c are mapped on an Au–Sb–Te triangular diagram. A β-Po-type rhombohedral structure appears before the crystal structure changes from As type (Sb) to α-Po type. Superconductivity is observed in the β-Po-type structure as well as in the α-Po-type structure. T_c increases with decreasing Te concentration toward the Te-free Au–Sb end of the diagram. A T_c of 8.1 K was achieved for the Au–Sb alloy with a typical composition of Au0.15Sb0.85. This T_c value is the highest among materials with the α-Po-type structure under ambient pressure. Our Au_0.125Sb_0.75Te_0.125 sample exhibits a weak metallic behavior in resistivity. The discrepancy in the normal state resistivity behaviors between the previous study and ours must originate from a difference in the number of lattice defects in the samples.