Phonon-mediated superconductivity in Na2CoSe2O: A first-principles study

Abstract

The recently discovered cobalt oxychalcogenide superconductor Na2CoSe2O has attracted great attention due to its interesting properties, such as superconductivity, quasi-two-dimensionality, low carrier concentration, and very high upper critical field [J. Cheng et al., J. Am. Chem. Soc. 146, 5908 (2024)]. Nevertheless, the underlying superconducting mechanism of Na2CoSe2O remains unclear and needs further theoretical clarification. In this work, we have systematically investigated the electronic structures, lattice dynamics, and superconducting properties of Na2CoSe2O by performing first-principles calculations. Our computational results suggest that the superconductivity in Na2CoSe2O originates from the strong electron-phonon coupling rather than the electronic correlation of Co 3d electrons. The calculated superconducting transition temperature Tc of 5.7 K agrees quite well with the experimental value, indicating that the superconducting pairing in Na2CoSe2O belongs to the conventional Bardeen-Cooper-Schrieffer (BCS) type. Additionally, we find that the spin-orbital coupling (SOC) effect can induce unique spin textures for the bands around the Fermi level, which may explain the experimentally observed high upper critical field and its anisotropy along the in-plane and out-of-plane directions. Inspired by the results of Na2CoSe2O, we also predict the CoSe2/Ca2N bilayer heterostructure as a two-dimensional (2D) superconductor with the superconducting Tc of 5.1 K. Our identification on the nature of superconductivity in Na2CoSe2O and prediction on the CoSe2/Ca2N superconductor call for future experimental verifications.

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