Discovery of a new phase in thin flakes of KV${}_3$Sb${}_5$ under pressure

We report results of magnetotransport measurements on KV${}_3$Sb${}_5$ thin flakes under pressure. Our zero-field electrical resistance reveals an additional anomaly emerging under pressure ($p$), marking a previously unidentified phase boundary $T^{\ast }$($p$). Together with the established $T_{\mathrm{C}\mathrm{D}\mathrm{W}}(p)$ and $T_c(p)$, denoting the charge-density-wave transition and a superconducting transition, respectively, the temperature-pressure phase diagram of KV${}_3$Sb${}_5$ features a rich interplay among multiple phases. The Hall coefficient evolves reasonably smoothly when crossing the $T^{\ast }$ phase boundary compared with the variation when crossing $T_{\mathrm{C}\mathrm{D}\mathrm{W}}$, indicating the preservation of the pristine electronic structure. The mobility spectrum analysis provides further insights into distinguishing different phases. Finally, our high-pressure quantum oscillation studies up to 31 T combined with density functional theory calculations further demonstrate that the new phase does not reconstruct the Fermi surface, confirming that the translational symmetry of the pristine metallic state is preserved.