Using first-principles density-functional theory calculations, we investigate the pressure-induced quantum phase transition (QPT) from the charge density wave (CDW) to the pristine phase in the layered kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ consisting of three-atom-thick $\mathrm{Sb}\text{−}{\mathrm{V}}_3\mathrm{Sb}\text{−}\mathrm{Sb}$ and one-atom-thick Cs layers. The CDW structure having the formation of trimeric and hexameric V atoms with buckled Sb honeycomb layers features an increase in the lattice parameter along the $c$ axis, compared with its counterpart pristine structure having the ideal ${\mathrm{V}}_3\mathrm{Sb}$ kagome and planar Sb honeycomb layers. Consequently, as pressure increases, the relatively smaller volume of the pristine phase contributes to reducing the enthalpy difference between the CDW and pristine phases, yielding a pressure-induced QPT at a critical pressure $P_c$ of $\approx 2$ GPa. Furthermore, we find that (i) the superconducting transition temperature $T_c$ increases around $P_c$ due to a phonon softening associated with the periodic lattice distortion of V trimers and hexamers and that (ii) above $P_c$, optical phonon modes are hardened with increasing pressure, leading to monotonic decreases in the electron-phonon coupling constant and $T_c$. Our findings not only demonstrate that the uniaxial strain along the $c$ axis plays an important role in the QPT observed in ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ but also provide an explanation for the observed superconductivity around $P_c$ in terms of a phonon-mediated superconducting mechanism.

• Received 13 July 2022
• Accepted 13 September 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.094801