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

Abstract

We have investigated superconductivity and structure in a gold-antimony-tellurium ternary alloy system (Au x Sb 1−x−y Te y ) synthesized under high pressure. We found that Au 0.125 Sb 0.75 Te 0.125 and AuSb 6 Te 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 Au 0.15 Sb 0.85 . This T c value is the highest among materials with the α-Po-type structure under ambient pressure. Our Au 0.125 Sb 0.75 Te 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.

Electronic Structure of Novel Superconductor AuSb6Te

“…The density of states (DOS) curve of AuSb 6 Te is shown in Fig.1. We can see that the DOS have a sharp peak just around the Fermi level (E F ).…”

“…AuSb 6 Te crystallizes in cubic structure with -Po type, so-called -phase [7]. We have assumed that the atoms are ordered as followings: Au in 1a (0,0,0), Sb in 3c (1/2,0,0) and 3d (1/2,1/2,0), and Te in 1b (1/2,1/2,1/2).…”

“…Moreover, hybridization makes this counting further difficult. Therefore we only compare the number of the 5d electrons of AuSb 6 Te with some typical ionic Au compounds. Table I shows the numbers of the 5d electrons of AuSb 6 Te, AuCl, CsAuCl 3 , and AuSe.…”

“…Apart from the quantitative estimation of |U eff |, this concept may be useful to search new superconductors. From this concept we have found a new superconductor AuSb 6 Te [6]. This compound was known to be a semiconductor [7], but our research has clarified that this compound is a superconductor with T c =6.7K.…”

“…In this paper, we have performed an ab-initio band structure calculation for AuSb 6 Te. Section 2 describes the framework of our calculation.…”