Distinct lattice and charge excitations in AV3Sb5 kagome superconductors

TL;DR

This study uses polarized Raman spectroscopy and theoretical modeling to reveal distinct lattice and charge excitation behaviors in AV3Sb5 kagome superconductors, elucidating their complex symmetry breaking phenomena.

Contribution

It demonstrates that lattice and charge excitations differ among AV3Sb5 compounds, providing new insights into their material-dependent symmetry breaking in the CDW phase.

Findings

Ubiquitous splitting of the E2g phonon mode in all compounds.

Distinct polarization dependences of CDW excitations among different alkali metals.

Insights into the charge order structure from combined experiments and modeling.

Abstract

The kagome superconductor family AV3Sb5 (A=Cs, Rb, K) provides a rich platform for exploring diverse electronic symmetry breaking phenomena, including superconductivity and various forms of density wave orders. Although these compounds share the identical lattice structure in the normal state, they exhibit distinct forms of symmetry breaking upon entering the charge density wave (CDW) phase, and the microscopic origin of which remain elusive. Here, we investigate the lattice and charge degrees of freedom in AV3Sb5 using angle-resolved polarized Raman spectroscopy. Our comprehensive polarization-resolved measurements reveal that the lifting of the twofold-degeneracy of the E2g phonon mode in the CDW phase-previously reported only in CsV3Sb5 with a 3 GHz splitting-also appears ubiquitously in the other two compounds. In contrast, the collective CDW excitations exhibit markedly different polarization dependences depending on the alkali-metal species. These distinct behaviors in the lattice and charge channels provide crucial insight into the enigmatic material-dependent symmetry breaking phenomena that appear in the CDW phase. Furthermore, our experiments, together with first-principles calculations and an effective Hamiltonian model, shed light on the nature of the charge order structure in AV3Sb5 kagome superconductors.