Charge order and superconductivity in extended Hubbard models for AV3Sb5 kagome metals

The Hubbard model on the kagome lattice is often considered as a minimal model to describe the rich low-temperature behavior of AV3Sb5 compounds (with A=K, Rb, Cs) [1], featuring charge-density waves (CDWs), superconductivity (SC), and possibly broken time-reversal symmetry. We investigate its ground-state properties when both onsite and nearest-neighbor Coulomb repulsions are considered at the van Hove filling. Our study is based on variational Jastrow-Slater wave functions which are capable of describing both CDW and SC phases and account for the effects of electronic correlation beyond the mean-field level. We reveal the presence of different repulsion-driven CDWs and, contrary to previous studies, the absence of ferromagnetism and charge- or spin-bond order. No signatures of chiral phases are detected. Remarkably, the CDWs triggered by the Coulomb repulsion possess charge disproportionations that are not compatible with the ones observed in AV3Sb5. As an alternative mechanism to stabilize charge order, we consider the electron-phonon interaction, modeled by coupling the hopping amplitudes to quantum phonons, as in the Su-Schrieffer-Heeger model. Our results show the instability towards a tri-hexagonal distortion with 2x2 periodicity, in a closer agreement with experimental findings [2].

[1] B. R. Ortiz, L. C. Gomes, J. R. Morey et al., Phys. Rev. Materials 3, 094407 (2019)

[2] F. Ferrari, F. Becca, R. Valentí, Phys. Rev. B 106, L081107 (2022)