Two-dimensional Superconductors, van der Waals Interactions, and the Dichalcogenides I
Investigating the superconducting state of 2H-NbS2 as seen by the vortex lattice
9:48 am – 10:00 amTransition metal dichalcogenides have sparked a lot of interest as they display several electronic orders, including charge density waves, Mott-insulating phases and superconductivity. The family of 2H-MX2 (M = Nb, Ti, Ta; X = S, Se) have similar electronic band structures in the normal state. Within this family, 2H-NbS2 stands out as the only one in which a CDW phase has not been observed. Furthermore, it has been proposed as a host for the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconducting state based on torque magnetometry, specific heat and thermal expansion measurements when the field is precisely perpendicular to the c-axis [1]. This implies that there is a strong anisotropy in the superconducting properties in and out of the basal plane.
In our study, we delve into the superconducting properties of 2H-NbS2, a classic anisotropic multi-band superconductor that is currently under much investigation due to the dramatic changes seen when high magnetic fields are aligned parallel to its hexagonal niobium planes. Using small-angle neutron scattering as a bulk-sensitive technique, we have investigated the vortex lattice in 2H-NbS2 and the effect of the superconducting anisotropy on it by changing the magnetic field orientation relative to the Nb planes. We find no changes in the observed superconducting anisotropy across our measured field range, and furthermore, we are able to fit all of the intensities of the measured vortex lattice scattering peaks at all angles with a single geometric mean of the London penetration depths in and out of plane. This is done using the anisotropic London theory, as originally postulated by Thiemann et al. [2], with the addition of a core-size exponential cut-off, and our results constitute the first complete validation of this longstanding model. Using this model, we are able to determine the two characteristic superconductor length scales: the penetration depth and the coherence length. Our results point to a predominant sampling of the larger superconducting gap in this material [3].
References
[1] C. Cho et al., Nature Comm. 12,3676 (2021).
[2] L. Thiemann et al., PRB. 39, 11406 (1989).
[3] A. Alshemi et al., Physical Review Research 6,033218 (2024)