Effect of nonhydrostatic pressure on the superconducting kagome metal CsV3Sb5

High-pressure single-crystal x-ray diffraction experiments reveal that the superconducting kagome metal CsV3Sb5 transforms from hexagonal (P6/mmm) to monoclinic (C2/m) symmetry above 10 GPa if nonhydrostatic pressure conditions are created in a diamond anvil cell with silicon oil as the pressure-transmitting medium. This is contrary to the behavior of CsV3Sb5 under quasihydrostatic conditions in neon, with the hexagonal symmetry retained up to at least 20 GPa. Monoclinic distortion leaves the kagome planes almost unchanged, but deforms honeycomb nets of the Sb atoms. While the onset of the distortion almost coincides with the reentrance of superconductivity, our ab initio density-functional calculations reveal only minor changes in the electronic structure compared to the quasihydrostatic case. In particular, Fermi surface reconstruction driven by the formation of interlayer Sb-Sb bonds is observed in both monoclinic and hexagonal CsV3Sb5 structures at high pressures and comes out as the likely cause for the reentrant behavior.