Ising Superconductivity and Signatures of Orbital FFLO State in Non-Centrosymmetric 3R-TaSe₂ Thin Flakes

Layered superconductors without inversion symmetry exhibit fantastic phenomena like spin-triplet, Ising pairing, and non-zero momentum of Cooper pairs. Identifying such unique compound and achieving accessible single crystals are rather challenging. Here, the sizable 3R-TaSe₂ single crystals are first grown upon precisely controlling the temperature gradient, and then its superconducting properties are studied as reducing thickness. The bulk 3R-TaSe₂ shows 3 × 3 charge-density-wave (CDW) transition at 114 K and superconductivity at 2.89 K. Its in-plane upper critical field ((Formula presented.)) is two times of Pauli-limited value (H_p). Contrasting with the three-fold symmetric lattice, the superconducting state exhibits a two-fold rotational symmetry under in-plane external magnetic fields, implying the possible s+p/d mixed states. More importantly, in two unit-cells (UC) 3R-TaSe₂, the (Formula presented.) >3H_p and the square-root relation of (Formula presented.) -T near T_c are hallmarks of Ising SC. In 4 UC and 8 UC flakes, orbital Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) states emerged between (T^*, H^*) = (0.91 T_c0, 0.37 H_p) and (T^*, H^*) = (0.76T_c0, 0.94 H_p). It can be explained by the indispensably interlayer orbital hopping under the context of Ising pairing. The results set the 3R-TaSe₂ as a platform to study the role of interplay between orbits and spins in electronically ordered states.