Abstract
This thesis systematically investigates the interplay between dimensional confinement, hydration, and superconductivity in potassium-doped tantalum disulfide (KTaS2) from the bulk down to the two-dimensional limit. To preserve the fragile intrinsic hydration state and minimize interfacial contamination, high-quality devices ranging from 120 nm to 10 nm were fabricated utilizing deterministic PDMS-assisted mechanical exfoliation and dry-release transfer techniques, combined with hexagonal boron nitride (h-BN) encapsulation. Comparative electrical transport measurements highlight the profound impact of water intercalation: while bulk anhydrous KTaS2 exhibits a superconducting transition temperature (Tc) of 4.6 K, the hydrated phase expands the van derWaals gap and enhances Tc to 5.6 K. Furthermore, whereas anhydrous thin-film devices suffer from a broadened, two-step transition due to spatial inhomogeneities, the PDMS-transferred hydrated devices maintain a sharp, single-step transition, confirming highly uniform water intercalation. Measurements on 120 nm hydrated devices confirm the strictly two-dimensional nature of this macroscopic superconducting phase via the observation of a Berezinskii- Kosterlitz-Thouless (BKT) transition at 4.82 K. Crucially, scaling the hydrated material down to the ultra-thin limit (18 nm and 10 nm) uncovers colossal critical field anisotropy and extreme angular sensitivity. The in-plane upper critical field of the 18 nm device survives well beyond 14 Tseverely violating the theoretical Pauli paramagnetic limit of roughly 9.6 Twhile the out-of-plane critical field is rapidly extinguished near 0.5 T. This immense resilience against in-plane magnetic fields provides compelling experimental evidence for Ising superconductivity in hydrated KTaS2, demonstrating that strong spinorbit coupling and broken out-of-plane inversion symmetry induce a spin-valley locking mechanism that effectively protects Cooper pairs from Pauli depairing.