Two-dimensional superconductivity in new niobium dichalcogenides-based bulk superlattices

TL;DR

This paper reports the discovery of two-dimensional superconductivity in newly synthesized niobium dichalcogenide-based bulk superlattices, demonstrating intrinsic 2D superconductivity with high anisotropy and exceeding Pauli limit, using a novel layered structure approach.

Contribution

The study introduces a new method to realize 2D superconductivity in bulk superlattices composed of niobium dichalcogenides and insulating spacers, expanding the material platform for 2D superconductors.

Findings

Both superlattices are type-II superconductors with T_c of 1 K and 1.25 K.

Intrinsic 2D superconductivity confirmed below Berezinskii-Kosterlitz-Thouless transition.

Upper critical field along ab plane exceeds Pauli limit in Ba₀.75ClNbSe₂.

Abstract

Transition metal dichalcogenides exhibit many unexpected properties including two-dimensional (2D) superconductivity as the interlayer coupling being weakened upon either layer-number reduction or chemical intercalation. Here we report the realization of 2D superconductivity in the newly-synthesized niobium dichalcogenides-based bulk superlattices Ba$_{0.75}$ClNbS$_{2}$ and Ba$_{0.75}$ClNbSe$_{2}$, which consists of the alternating stacking of monolayer $H$-NbS$_{2}$ (or $H$-NbSe$_{2}$) and monolayer inorganic insulator spacer Ba$_{0.75}$Cl. Magnetic susceptibility and resistivity measurements show that both superlattices belong to type-II superconductor with $T_{c}$ of 1 K and 1.25 K, respectively. Intrinsic 2D superconductivity is confirmed for both compounds below a Berezinskii-Kosterlitz-Thouless transition and a large anisotropy of the upper critical field. Furthermore, the upper critical field along $ab$ plane ($H_{c2}^{\parallel ab}$) exceeds the Pauli limit ($\mu_{0}H_{p}$) in Ba$_{0.75}$ClNbSe$_{2}$, highlighting the influence of spin-orbit interactions. Our results establish a generic method for realizing the 2D superconducting properties in bulk superlattice materials.