Bulk electronic structure of AV3Sb5 (A = K, Cs) studied by hard x-ray photoemission spectroscopy. Possibility of bond order without charge disproportionation

The bulk electronic structure of AV3Sb5 (A=K, Cs) has been investigated by means of hard x-ray photoemission spectroscopy (HAXPES). The asymmetric shape of V and Sb core level peaks indicates that the V 3d and Sb 5p electrons are involved in the conduction band. The absence of a satellite structure in the V 2p HAXPES spectra shows a weak electronic correlation in the V 3d states. Splitting of the V 2p peak is not observed in the density wave phase indicating the charge disproportionation between the V sites is undetectably small, consistent with the weakness of the on-site electronic correlation and the possibility of bond order. The Sb 4d5/2 binding energy agrees with that of the Cs-terminated surface, indicating that the electronic structure of the V3Sb5 layer just below the Cs surface is close to the bulk.