Charge and Electronic Correlations in CsV₃Sb₅ from Microscopic Probes

Kagome materials, with their geometrical frustration due to corner-sharing triangles, possess electronic band structures that feature saddle points, flat-bands and Dirac cones. The interplay between topology and band fillings at these points can promote enhanced electronic interactions that lead to the formation of correlated phenomena such as superconductivity, charge density wave (CDW) order and anomalous Hall effect. Vanadium-based kagome metals AV₃Sb₅ (A = Cs, K, Rb) are not only notable for the coexistence of long-range CDW order and superconductivity, but also for their complex interplay. Strictly speaking, knowing the true nature of the CDW can help explain why either the CDW enhances or suppresses the superconducting transition. Here, we focus on CsV₃Sb₅ and investigate the local charge distribution and changes of the crystalline structure using nuclear quadrupole resonance (NQR) and first-principle calculations. By studying the temperature-dependence of the NQR spectrum, we identify the microscopic nature of the CDW state. Finally, we show that understanding the true microscopic nature of the CDW may provide a deeper insight into the intertwined superconducting order and, more broadly, the behavior of correlated materials.