Crossover from\nConventional to Unconventional Superconductivity\nin 2M-WS<sub>2</sub>

Leveraging the reciprocal-space proximity effect between\nsuperconducting\nbulk and topological surface states (TSSs) offers a promising way\nto topological superconductivity. However, elucidating the mutual\ninfluence of bulk and TSSs on topological superconductivity remains\na challenge. Here, we report pioneering transport evidence of a thickness-dependent\ntransition from conventional to unconventional superconductivity in\n2M-phase WS<sub>2</sub> (2M-WS<sub>2</sub>). As the sample thickness\nreduces, we see clear changes in key superconducting metrics, including\ncritical temperature, critical current, and carrier density. Notably,\nwhile thick 2M-WS<sub>2</sub> samples show conventional superconductivity,\nwith an in-plane (IP) upper critical field constrained by the Pauli\nlimit, samples under 20 nm exhibit a pronounced IP critical field\nenhancement, inversely correlated with 2D carrier density. This marks\na distinct crossover to unconventional superconductivity with strong\nspin-orbit-parity coupling. Our findings underscore the crucial role\nof sample thickness in accessing topological states in 2D topological\nsuperconductors, offering pivotal insights into future studies of\ntopological superconductivity.