Weak electronic correlations in the kagome superconductor A V3Sb5 (A= K, Rb, Cs)

The kagome metals AV3Sb5 (A=K, Rb, Cs) have recently received enormous attention as they exhibit nontrivial topological electronic structure, flat band, unconventional intertwined charge density wave (CDW), anomalous Hall effect, and superconductivity. However, it is still controversial whether or not electronic correlations play an important role in these novel phenomena. Here we perform an extensive investigation on AV3Sb5 (A=K, Rb, Cs) with density functional theory plus dynamical mean field theory calculations. Our results indicate the electronic correlations effects are in the weak regime in both the normal state and the CDW state. The value of effective mass-enhancement m∗/mDFT is about 1.3, and it is barely changed at temperatures ranging 50-900 K in the normal state. Our static susceptibility calculations with the normal structure show that static susceptibility has a weak qz dependence and the Fermi-surface nesting mechanism does not work in this system. In the CDW state with the inverse Star of David structure, the spectral function opens a CDW gap at the Fermi level below TCDW (50 K) compared with the normal state above TCDW (300 K). We find that there exists orbital multiplicity at the Fermi level owing to two nonequivalent V atoms in CDW states, which may have an important role in forming the CDW order.