Investigating the superconducting state of 2H−NbS2 as seen by the vortex lattice

Abstract

2H−NbS2 is a classic example of an anisotropic multiband superconductor, with significant recent work focusing on the interesting responses seen when high magnetic fields are applied precisely parallel to the hexagonal niobium planes. It is often contrasted with its sister compound 2H−NbSe2 because they have similar onset temperatures for superconductivity, but 2H−NbS2 has no charge density wave whereas in 2H−NbSe2 the charge density wave order couples strongly to the superconductivity. Using small-angle neutron scattering, a bulk-sensitive probe, we have studied the vortex lattice and how it responds to the underlying superconducting anisotropy. This is done by controlling the orientation of the field with respect to the Nb planes. The superconducting anisotropy, Γac=7.07±0.2, is found to be field independent over the range measured (0.15 to 1.25 T), and the magnetic field distribution as a function of the applied magnetic field is found to be in excellent quantitative agreement with anisotropic London theory modified with a core-size cutoff correction, providing the first complete validation of this model. We find values of λab=141.9±1.5 nm for the in-plane London penetration depth, and λc∼1µm for the out-of-plane response. The field-independence indicates that we are primarily sampling the larger of the two gaps generating the superconductivity in this material.

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