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

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Abstract
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 () is two times of Pauli‐limited value (Hp). 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 >3Hp and the square‐root relation of ‐T near Tc 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 Tc0, 0.37 Hp) and (T*, H*) = (0.76Tc0, 0.94 Hp). 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.
Funding Information
  • National Natural Science Foundation of China (52250308, 61971035, 12334002)

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