Charge density wave and superconductivity in the kagome metal CsV3Sb5 around a pressure-induced quantum critical point

Abstract

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 CsV3Sb5 consisting of three-atom-thick Sb−V3Sb−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 V3Sb 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 Pc of ≈2 GPa. Furthermore, we find that (i) the superconducting transition temperature Tc increases around Pc due to a phonon softening associated with the periodic lattice distortion of V trimers and hexamers and that (ii) above Pc, optical phonon modes are hardened with increasing pressure, leading to monotonic decreases in the electron-phonon coupling constant and Tc. Our findings not only demonstrate that the uniaxial strain along the c axis plays an important role in the QPT observed in CsV3Sb5 but also provide an explanation for the observed superconductivity around Pc in terms of a phonon-mediated superconducting mechanism.

Source-reported materials — not catalogue approval

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