Colossal c-Axis Response and Lack of Rotational Symmetry Breaking within the Kagome Planes of the CsV₃Sb₅ Superconductor

The kagome materials AV3Sb5 (A = K, Rb, Cs) host an intriguing interplay between unconventional superconductivity and charge-density waves. Here, we investigate CsV3Sb5 by combining high-resolution thermal-expansion, heat-capacity, and electrical resistance under strain measurements. We directly unveil that the superconducting and charge-ordered states strongly compete, and that this competition is dramatically influenced by tuning the crystallographic c axis. In addition, we report the absence of additional bulk phase transitions within the charge-ordered state, notably associated with rotational symmetry breaking within the kagome planes. This suggests that any breaking of the C6 invariance occurs via different stacking of C6-symmetric kagome patterns. Finally, we find that the charge-density-wave phase exhibits an enhanced A1g-symmetric elastoresistance coefficient, whose large increase at low temperature is driven by electronic degrees of freedom.