Crossover from Conventional to Unconventional Superconductivity in 2M-WS<sub>2</sub>.

Samarawickrama, Piumi; McBride, Joseph; Gautam, Sabin; Fu, ZhuangEn; Watanabe, Kenji; Taniguchi, Takashi; Wang, Wenyong; Tang, Jinke et al. · Nano Lett · 2024

basic_science · Level V

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Abstract

Leveraging the 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 WS<sub>2</sub> (2M-WS<sub>2</sub>). 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-WS<sub>2</sub> 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.