Two-dimensional superconductivity and anomalous vortex dissipation in newly-discovered transition metal dichalcogenide-based superlattices

TL;DR

This study reports the discovery of 2D superconductivity with unusual vortex dissipation behaviors in bulk TMD-based superlattices, revealing new quantum phases and strong fluctuation effects in these materials.

Contribution

It demonstrates intrinsic 2D superconductivity in bulk TMD superlattices with high critical fields and novel vortex dynamics, expanding the understanding of layered superconductor properties.

Findings

Intrinsic 2D superconductivity below BKT transition

Upper critical field exceeds Pauli limit, especially in Ba0.75ClTaSe2

Observation of vortex dissipation due to Josephson vortex motion

Abstract

Properties of layered superconductors can vary drastically when thinned down from bulk to monolayer, owing to the reduced dimensionality and weakened interlayer coupling. In transition metal dichalcogenides (TMDs), the inherent symmetry breaking effect in atomically thin crystals prompts novel states of matter, such as Ising superconductivity with an extraordinary in-plane upper critical field. Here, we demonstrate that two-dimensional (2D) superconductivity resembling those in atomic layers but with more fascinating behaviours can be realized in the bulk crystals of two new TMD-based superconductors Ba0.75ClTaS2 and Ba0.75ClTaSe2. They comprise an alternating stack of H-type TMD layers and Ba-Cl layers. In both materials, intrinsic 2D superconductivity develops below a Berezinskii-Kosterlitz-Thouless transition. The upper critical field along ab plane exceeds the Pauli limit (Hp); in particular, Ba0.75ClTaSe2 exhibits an extremely high in plane Hc2 (14Hp) and a colossal superconducting anisotropy of 150. Moreover, the temperature-field phase diagram of Ba0.75ClTaSe2 under an in-plane magnetic field contains a large phase regime of vortex dissipation, which can be ascribed to the Josephson vortex motion, signifying an unprecedentedly strong fluctuation effect in TMD-based superconductors. Our results provide a new path towards the establishment of 2D superconductivity and novel exotic quantum phases in bulk crystals of TMD-based superconductors.