Anomalous enhancement of charge density wave in kagome superconductor CsV3Sb5 approaching the 2D limit

The recently discoveredkagomemetals AV(3)Sb(5) (A = Cs, Rb, K) exhibit a variety of intriguing phenomena, such as a charge density wave (CDW) with timereversal symmetry breaking and possible unconventional superconductivity. Here, we report a rare non-monotonic evolution of the CDW temperature (T-CDW) with the reduction of flake thickness approaching the atomic limit, and the superconducting transition temperature (T-c) features an inverse variation with T-CDW. T-CDW initially decreases to aminimum value of 72 K at 27 layers and then increases abruptly, reaching a record-high value of 120 K at 5 layers. Raman scatteringmeasurements reveal aweakened electron-phonon coupling with the reduction of sample thickness, suggesting that a crossover from electron-phonon coupling to dominantly electronic interactions could account for the non-monotonic thickness dependence of T-CDW. Our work demonstrates the novel effects of dimension reduction and carrier doping on quantum states in thin flakes and provides crucial insights into the complex mechanism of the CDW order in the family of AV(3)Sb(5) kagome metals.

Automated summary

The recently discovered kagome metals AV(3)Sb(5) (A = Cs, Rb, K) exhibit intriguing phenomena including charge density wave (CDW) with time-reversal symmetry breaking and possible unconventional superconductivity. In this study, we observe a non-monotonic evolution of CDW temperature (T-CDW) with flake thickness reduction towards the atomic limit, and the superconducting transition temperature (T-c) features an inverse variation with T-CDW. We propose that the weakening of electron-phonon coupling and crossover to dominantly electronic interactions contribute to the non-monotonic thickness dependence of T-CDW.