Dynamical study of the origin of the charge density wave in AV₃Sb₅ (A=K, Rb, Cs) compounds

Systems containing the ideal kagome lattice can exhibit several distinct and novel exotic states of matter. One example of such systems is a recently discovered AV3Sb5 (A = K, Rb, and Cs) family of compounds. Here, the coexistence of the charge density wave (CDW) and superconductivity is observed. Here, we study the dynamic properties of the AV3Sb5 systems in context of origin of the CDW phase. We show and discuss the structural phase transition from P6/mmm to C2/m symmetry that are induced by the presence of phonon soft modes. We conclude that the CDW observed in this family of compounds is a consequence of the atom displacement, from the high symmetry position of the kagome net, in low-temperature phase. Additionally, using the numerical ab initio (DFT) methods, we discuss the charge distribution on the AV3Sb5 surface. We show that the observed experimental stripe-like modulation of the surface, can be related to surface reconstruction and manifestation of the three dimensional 2x2x2 bulk CDW. Finally, the consequence of realization of the C2/m structure on the electronic properties are discussed. We show that the electronic band structure reconstruction and the accompanying modification of density of states correspond well to the experimental data.