Characterizations of Anisotropic Superconductivity in (BiSe)_1+δNbSe₂

Abstract

Anisotropy of superconductivity in misfit layered compounds (BiSe)1+δNbSe2 was studied. We synthesized single crystals of (BiSe)1+δNbSe2 using CsCl/KCl flux method. There existed two phases with different T c depending on the starting composition δ, although their structures were almost unaffected by changing δ. Anisotropy of the upper critical field was determined by magneto-resistance measurements with various out-of-plane and in-plane field angles. The out-of-plane anisotropy of H c2 showed a cusp-like behavior for fields close to ab-plane similar to that predicted by 2D Tinkham model. Furthermore, a clear two-fold symmetry was observed in the in-plane angular dependence of H c2.

Two-dimensional Superconductivity in Misfit Layered Compound (BiSe)1.10NbSe2

“…The field is applied along three principal axes. The critical temperature (T c ) is estimated as 2.7 K, somewhat higher than the reported value [2], but within a range of our former study [3]. This suggeseted that (BiSe) 1.10 NbSe 2 is also anisotropic in the in-plane direction, which can be attributed to an averaged orthorhombic structure due to the mismatch of two subsystems.…”

“…(BiSe) 1.10 NbSe 2 is one of superconducting misfit layer compounds with T c of 2.6-3.0 K, composed of a semiconductor BiSe and a superconducting transition metal dichalcogenide NbSe 2 [2,3]. In our previous report, the multi-phase character depending on the nominal composition, the anisotropic superconductivity, and its relevance to another ternary system consisting of the same elements, Nb doped Bi 2 Se 3 , were discussed.…”