Transition metal dichalcogenides exhibit multiple polymorphs that enable the exploration of diverse quantum states, including valley-selective spin polarization, the valley Hall effect, Ising superconductivity, and nontrivial topology. Monolayer 2H-NbSe2 is a promising candidate for realizing Ising superconductivity due to its spin-split, out-of-plane spin-polarized states arising from inversion symmetry breaking and strong spin-orbit coupling. In contrast, bulk 2H-NbSe2 retains inversion symmetry and lacks spin splitting, limiting its suitability for hosting Ising superconductivity. Here, we report the growth of high-quality single crystals of the acentric bulk superconducting polymorph, 4H-NbSe2, which intrinsically breaks the inversion symmetry and supports valley-selective spin-polarized states. Magnetization and resistivity measurements reveal anisotropic superconductivity, with the in-plane upper critical field exceeding the Pauli limit, while out-of-plane fields suppress superconductivity more rapidly, before reaching the Pauli limit, which strongly suggests the presence of Ising pairing. First-principles calculations and symmetry analysis confirm significant valley-selective spin splitting with out-of-plane spin polarization, further supporting the emergence of Ising superconductivity in 4H-NbSe2. These results establish 4H-NbSe2 as a robust bulk platform to investigate Ising superconductivity and valley-selective phenomena in transition-metal dichalcogenides.
@article{arxiv.2506.09413,
title = {Ising superconductivity in bulk layered non-centrosymmetric 4H-NbSe2},
author = {Chandan Patra and Tarushi Agarwal and Rahul Verma and Poulami Manna and Shashank Srivastava and Ravi Shankar Singh and Mathias S. Scheurer and Bahadur Singh and Ravi Prakash Singh},
journal= {arXiv preprint arXiv:2506.09413},
year = {2025}
}