Charge density wave, superconductivity, and nontrivial topology in monolayer NbSi2As4

Abstract

Charge density wave (CDW), superconductivity, nontrivial topology, and their interplay have garnered significant attention in condensed matter physics. In this Letter, we predicted α2−NbSi2As4 as a ground-state CDW candidate, combining with superconductivity and nontrivial topology within the two-dimensional (2D) MA2Z4 family. Using first-principles calculations, we systematically investigated its electronic structure, vibrational properties, CDW instability, and superconductivity. The α2−NbSi2As4 monolayer shares a similar crystal field with 2H−NbSe2, resulting in a comparable Fermi-surface topology that enables the formation of CDW. The CDW instability arises from the electron-phonon coupling between Nb-d orbitals and longitudinal acoustic phonons from the Nb-xy vibrational mode. Electron doping and tensile strain can suppress the CDW instability, leading to 2D superconductivity with critical temperatures of 5.73 and 5.11 K under 0.2 e−/f.u. and 2.3% strain, respectively. The strong hybridization between Nb-d and As-p orbitals causes the metallic band crossing the Fermi level to intersect with lower bands, forming six topologically nontrivial Dirac points as described by a three-band tight-binding model. This nontrivial topology coexists with both CDW and superconductivity within the same metallic band. The ground-state CDW in α2−NbSi2As4 monolayer offers a potential platform for exploring the interplay of many-body instabilities and topological physics.

Source-reported materials — not catalogue approval

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