Superconductivity and band topology in the double-layer honeycomb structure compounds X2C2 (X=P, Ta, W)

Abstract

Double-layer honeycomb (DLHC) materials exhibit tunable electronic properties and enhanced stability over single-layer/bulk honeycomb forms, but existing experimental research has predominantly focused on semiconducting systems, while theoretical studies on superconductivity remain sparse. Through first-principles calculations, we identified three stable metallic DLHC superconductors: P2C2,Ta2C2, and W2C2, with superconducting transition temperature Tc of 18.3, 6.8, and 4.8 K, respectively. Additionally, anisotropic Migdal-Eliashberg theory predicts that P2C2 is a single-gap superconductor with a Tc of 27.2 K. The element-dependent electronic characteristics and superconductivity of them are studied. It is revealed that P2C2 exhibits mixed ionic-covalent bonding, with superconductivity originating from the coupling between p-orbital electrons and atomic vibrations of both P and C, highlighting P-C synergy. Conversely, Ta2C2 and W2C2, which contain the transition metal elements Ta and W, display ionic character, where superconductivity is governed by the coupling between d orbitals electrons and vibration modes of metal atoms. These comparative results reveal element-specific orbital mechanisms in quantum materials. Additionally, all compounds exhibit nontrivial band topology, providing a tunable platform that may host topological superconductivity.

Source-reported materials — not catalogue approval

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