Role of Apical Ions in the CDW Phases of AV3Sb5 Kagome Metals

Charge density wave (CDW) instabilities of AV3Sb5 Kagome metals can be understood to emerge from a single Kagome plane, but the low energy CDW phases also involve an out-of-plane modulation of the crystal structure. This raises the question if other ions, such as the apical Sb's, have any role in determining the structural energy landscape. In this talk, using first principles calculations, we show that the apical Sb ions are essential in determining the energy scale of the CDW phases. We also discuss the possible connections of this observations with the nature of the superconducting order parameter in these systems.