Crossover from Conventional to Unconventional Superconductivity in 2M-WS2

TL;DR

This study demonstrates a thickness-dependent transition from conventional to unconventional superconductivity in 2M-WS2, highlighting the influence of sample thickness on topological superconducting states and critical magnetic field behavior.

Contribution

It provides the first transport evidence of a crossover from conventional to unconventional superconductivity in 2M-WS2 as thickness decreases, emphasizing the role of spin-orbit coupling and topological states.

Findings

Thinner 2M-WS2 samples show enhanced in-plane critical fields.

A clear transition from conventional to unconventional superconductivity occurs below 20 nm.

Sample thickness critically influences topological superconducting properties.

Abstract

Leveraging reciprocal-space proximity effect between superconducting bulk and topological surface states (TSSs) offers a promising way to topological superconductivity. However, elucidating the mutual influence of bulk and TSSs on topological superconductivity remains a challenge. Here, we report pioneering transport evidence of a thickness-dependent transition from conventional to unconventional superconductivity in 2M-phase WS2 (2M-WS2). As the sample thickness reduces, we see clear changes in key superconducting metrics, including critical temperature, critical current, and carrier density. Notably, while thick 2M-WS2 samples show conventional superconductivity, with an in-plane (IP) upper critical field constrained by the Pauli limit, samples under 20 nm exhibit a pronounced IP critical field enhancement, inversely correlated with 2D carrier density. This marks a distinct crossover to unconventional superconductivity with strong spin-orbit-parity coupling. Our findings underscore the crucial role of sample thickness in accessing topological states in 2D topological superconductors, offering pivotal insights into future studies of topological superconductivity.