First-principles study of the electronic structure, Z2 invariant and quantum oscillation in the kagome material CsV3Sb5

TL;DR

This study uses density functional theory to analyze the electronic structure, topological invariants, and quantum oscillations of CsV3Sb5, revealing its topological nature, lattice instability, and Fermi surface reconstruction associated with charge density wave order.

Contribution

It provides the first comprehensive DFT analysis of CsV3Sb5's electronic, topological, and phononic properties, including the calculation of Z2 invariants and quantum oscillation frequencies.

Findings

CsV3Sb5 exhibits lattice instability in pristine form.

Transition to a stable 2x2x1 charge density wave phase occurs.

The material has a strong topological Z2 invariant indicating topological nontriviality.

Abstract

This work presents a detailed study of the electronic structure, phonon dispersion, Z2 invariant calculation, and Fermi surface of the newly discovered kagome superconductor CsV3Sb5, using density functional theory (DFT). The phonon dispersion in the pristine state reveals two negative modes at the M and L points of the Brillouin zone, indicating lattice instability. CsV3Sb5 transitions into a structurally stable 2x2x1 charge density wave (CDW) phase, confirmed by positive phonon modes. The electronic band structure shows several Dirac points near the Fermi level, with a narrow gap opening due to spin-orbit coupling (SOC), though the effect of SOC on other bands is minimal. In the pristine phase, this material exhibits a quasi-2D cylindrical Fermi surface, which undergoes reconstruction in the CDW phase. We calculated quantum oscillation frequencies using Onsager's relation, finding good agreement with experimental results in the CDW phase. To explore the topological properties of CsV3Sb5, we computed the Z2 invariant in both pristine and CDW phases, resulting in a value of (u0; u1u2u3) = (1; 000), suggesting the strong topological nature of this material. Our detailed analysis of phonon dispersion, electronic bands, Fermi surface mapping, and Z2 invariant provides insights into the topological properties, CDW order, and unconventional superconductivity in AV3Sb5 (A = K, Rb, and Cs).