The nature of the CDW in Kagome Superconductors AV3Sb5 from the perspective of electronic structure

The recently discovered layered kagome metals AV3Sb5 (A=K, Rb, Cs) have attracted much attention because of their unique combination of superconductivity, charge density wave (CDW) order, and nontrivial band topology. The CDW order with an in-plane 2x2 reconstruction is found to exhibit exotic properties, such as time-reversal symmetry breaking and rotational symmetry breaking. However, the nature of the CDW, including its dimensionality, structural pattern, and effect on electronic structure, remains elusive despite intense research efforts. Here, we present a comprehensive study on the electronic structure of AV3Sb5 by combining angle-resolved photoemission spectroscopy with Density Functional theory calculations. Apart from the energy shift of van Hove singularities, we observe doubleband splittings for V d-orbital bands in the CDW phase, which provides essential information for revealing the dimensionality and pattern of the CDW order. Our calculations show that three-dimensional CDW orders containing stacking of Star-of-David and Tri-Hexagonal patterns along the c axis can quantitatively reproduce the experimental features. These results provide crucial insights into the nature and distortion pattern of the CDW order, and its signature in the electronic structure, thereby laying down the basis for a substantiated understanding of the exotic properties in the family of AV3Sb5 kagome metals.