Surface Effect and Termination-Dependent Charge Order Instability in Kagome Superconductor CsV3Sb5

Kagome superconductors AV3Sb5 (A = K, Rb, Cs) exhibit intertwined symmetry-breaking orders, including charge density wave (CDW), superconductivity, and time-reversal symmetry breaking (TRSB), yet their relationship, nature, and experimental detections remain under intense debate. At the heart of these controversies lies a critical yet often overlooked factor: the surface effect, which may engineer distinct technique-dependent observations. By combining density functional theory calculations and ARPES measurements, we unveil the important role of surface effect on the CDW instability and electronic reconstruction in CsV3Sb5. The surface CDW instability is much reduced on the Cs and Sb terminations but well-preserved on half-Cs termination. On the Cs-terminated surface, the interlayer expansion induces quantum confinement and two-dimensional quantum well states. These results explain the diversity of surface band structures observed in AV3Sb5, potentially reconcile conflicting observations of superconductivity and TRSB between bulk- and surface-sensitive probes, and offer a new perspective on studying exotic phenomena in AV3Sb5.