Highly Isotropic In-plane Upper Critical Field in the Anisotropic s-Wave Superconductor 2H-NbSe2

Abstract

Resistivity measurements for a layered transition metal dichalcogenide 2H-NbSe2 were performed to investigate the in-plane anisotropy of the upper critical field (Hc2) for magnetic fields up to 14.5 T at temperatures down to 2.0 K. For fields rotated within the basal plane, the in-plane anisotropy of a characteristic field H∗ (defined as the field strength at which the resistivity reaches zero) showed twofold symmetry at low temperatures. On the basis of this result, the in-plane anisotropy of Hc2 and the superconducting gap structure in 2H-NbSe2 are discussed.