Evolution of three-dimensional electronic structure in kagome superconductor CsV₃Sb₅

The effect of out-of-plane dimensionality on correlated quasi-two-dimensional (2D) materials has become increasingly evident. Recently, CsV₃Sb₅ has attracted much attention as the first quasi-2D kagome superconductor. While the kagome layers are 2D in nature, interlayer-interaction has been considered crucial in this system, and 3D charge density wave (CDW) has been observed. Here, we reveal the 3D electronic structure in CsV₃Sb₅, using angle-resolved photoemission spectroscopy (ARPES), complemented by scanning tunneling microscope (STM) and core level measurements. The complete 3D electronic structure of CsV₃Sb₅ in high temperature normal state are revealed, which agree well with density functional theory (DFT) calculations. New electron energy bands are observed in low temperature state, which exhibit clearly periodicities along the out-of-plane momentum (K_Z). STM and core level measurements further indicate that the low temperature band reconstruction mainly appears on regions where the 3D CDW is most clearly identified. Our results reveal a direct response to the three-dimensionality of CDW in single-particle spectral function, and establish an electronic platform to examine the exotic phenomena beyond 2D limit in kagome superconductors.