The kagome metal CsV₃Sb₅ is an ideal platform to study the interplay between topology and electron correlation. To understand the fermiology of CsV₃Sb₅, intensive quantum oscillation (QO) studies at ambient pressure have been conducted. However, due to the Fermi surface reconstruction by the complicated charge density wave (CDW) order, the QO spectrum is exceedingly complex, hindering a complete understanding of the fermiology. Using a special anvil cell technique we developed [1,2], we directly map the Fermi surface of the pristine CsV₃Sb₅ by measuring Shubnikov-de Haas QOs up to 29 T under pressure, where the CDW order is completely suppressed [3]. The QO spectrum of the pristine CsV₃Sb₅ is significantly simpler than the one in the CDW phase, and the detected oscillation frequencies agree well with our density functional theory calculations. In particular, a frequency as large as 8,200~T is detected. Pressure-dependent QO studies further reveal a weak but noticeable enhancement of the quasiparticle effective masses on approaching the critical pressure where the CDW order disappears, hinting at the presence of quantum fluctuations. Our high-pressure QO results reveal the large, unreconstructed Fermi surface of CsV₃Sb₅, paving the way to understanding the parent state of this intriguing metal in which the electrons can be organized into different ordered states.

[1] W. Zhang et al., Nano Lett. 23, 872 (2023)

[2] J. Xie et al., Nano Lett. 21, 9310 (2021)

[3] W. Zhang et al., Proc. Natl. Acad. Sci. USA 121, e2322270121 (2024)