Doping evolution of the electronic response of the kagome metal Cs(V1-xTix)3Sb5

Abstract

The vanadium-based kagome metal CsV3Sb5 has drawn significant interest since it exhibits a wide variety of intriguing topological phases and electronic instabilities. A prominent example includes an unconventional charge-density wave (CDW), which is associated with the Van Hove singularities (vHss). Hole doping of the system via substitution of Ti for V is expected to shift the vHss, providing an effective way to tune the Fermi surface instabilities in CsV3Sb5. We investigate the optical response of Cs(V1-xTix)3Sb5 (x = 0, 0.01, 0.02, and 0.06) single crystals by utilizing infrared spectroscopy. The infrared signature of the CDW order, i.e., the decrease in the low-energy spectral weight and the appearance of the absorption peak at about 200 meV, is suppressed upon Ti doping (x = 0.02) and completely disappears for x = 0.06. Nevertheless, the ratio of the CDW gap ACDW to the CDW transition temperature (TCDW), i.e., 2ACDW/kBTCDW is increased with Ti substitution. In the normal state, the spectral weight of the intraband response is abruptly suppressed with Ti doping (x 0.02), suggesting a significant increase in the effective mass of the itinerant carriers due to the shift of the vHs toward the Fermi level. The evolutions of the CDW phase and the normal-state charge dynamics reveal the crucial role of the electronic correlations in the Cs(V1-xTix)3Sb5 system.