New kagome prototype materials: discovery of KV3Sb5,RbV3Sb5 , and CsV3Sb5

In this work, we present our discovery and characterization of a new kagome prototype structure, KV₃Sb₅. We also present the discovery of the isostructural compounds RbV₃Sb₅ and CsV₃Sb₅. All materials exhibit a structurally perfect two-dimensional kagome net of vanadium. Density-functional theory calculations indicate that the materials are metallic, with the Fermi level in close proximity to several Dirac points. Powder and single-crystal syntheses are presented, with postsynthetic treatments shown to deintercalate potassium from single crystals of KV₃Sb₅. Considering the proximity to Dirac points, deintercalation provides a convenient means to tune the Fermi level. Magnetization measurements indicate that KV₃Sb₅ exhibits behavior consistent with a the Curie-Weiss model at high temperatures, although the effective moment is low (0.22μ_B per vanadium ion). An anomaly is observed in both magnetization and heat capacity measurements at 80 K, below which the moment is largely quenched. Elastic neutron scattering measurements find no obvious evidence of long-range or short-range magnetic ordering below 80 K. The possibility of an orbital-ordering event is considered. Single-crystal resistivity measurements show the effect of deintercalation on the electron transport and allow estimation of the Kadowaki-Woods ratio in KV₃Sb₅. We find that A/γ²~61μOhm cm mol²_FU K²J^-2, suggesting that correlated electron transport may be possible. KV₃Sb₅ and its cogeners RbV₃Sb₅ and CsV₃Sb₅ represent a new family of kagome metals, and our results demonstrate that they deserve further study as potential model systems.