Superconductivity and valence state in layered single-crystal HfAs1.67Te0.12

Abstract

We report a detailed study on single crystals of HfAs1.67Te0.12 within a PbFCl-type layered structure. The single crystals of the title compound were successfully grown using a chemical transport reaction. The temperature dependence of electrical resistivity , AC magnetic susceptibility and specific heat C(T) show a bulk superconductivity with transition temperature Tc = 1.67 K. The jump of C/T at Tc is comparable to the traditional BCS weak-coupling model. A full H–T phase diagram is established using the results of and C(T) under fields, suggesting a rather weak anisotropy [( of 1.8 in orbital limit dominated three-dimension-like superconducting system. The mixed-valence states of Hf and As observed in the binding energy from x-ray photoelectron spectroscopy are consistent with the single-crystal x-ray diffraction analysis, indicating that the As–Te disorder prefers to occur in the [HfAs] layer and a large amount of vacancies are present in tetragonal As layer. As compared to HfAs1.7Se0.2 (Tc = 0.52 K), a positive-like vacancy effect on Tc has been confirmed in HfAs1.67Te0.12. The analysis of the Hall coefficient implies that the hole-type carriers dominate the transport properties, which is in good agreement with the hole pockets at Fermi surface obtained in a band structure calculation. The detailed study of single-crystal HfAs1.67Te0.12 provides a possible candidate to discuss the non-magnetic Kondo effect.