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Exotic quantum solids can host electronic states that spontaneously break rotational symmetry of the electronic structure, such as electronic nematic phases and unidirectional charge density waves (CDWs). When electrons couple to the lattice, uniaxial strain can be used to anchor and control this electronic directionality. Here, we reveal an unusual impact of strain on unidirectional “smectic” CDW orders in kagome superconductors ${\mathrm{AV}}_3{\mathrm{Sb}}_5$using spectroscopic-imaging scanning tunneling microscopy. We discover local decoupling between the smectic electronic director axis and the direction of anisotropic strain. While the two can generally be aligned along the same direction in regions of a small CDW gap, the tendency for alignment decreases in regions where the CDW gap is the largest. This feature, in turn, suggests nanoscale variations in smectic susceptibility, which we attribute to a combination of local strain and electron correlation strength. Overall, we observe an unusually high decoupling rate between the smectic electronic director of the three-state Potts order and anisotropic strain, revealing weak smectoelastic coupling in the CDW phase of kagome superconductors. This finding is phenomenologically different from the extensively studied nematoelastic coupling in the Ising nematic phase of Ising nematic phase of Fe-based superconductor bulk single crystals, providing a contrasting picture of how strain can control electronic unidirectionality in different families of quantum materials. Published by the American Physical Society2025 

Kagome metals have emerged as a frontier in condensed matter physics due to their potential to host exotic quantum states. Among these, CsV₃Sb₅has attracted significant attention for the unusual coexistence of charge density wave (CDW) order and unconventional superconductivity, presenting an ideal system for exploring the emergent phenomena from the interplay of phonons, electronic fluctuations, and topological effects. The nature of CDW formation in CsV₃Sb₅is unconventional and has sparked considerable debate. In this study, we examine the origin of the CDW state via ab initio finite-temperature simulations of the lattice dynamics. Through a comparative study of CsV₃Sb₅and 2H-NbSe₂, we demonstrate that the experimental absence of phonon softening—a hallmark of conventional CDW transition—in CsV₃Sb₅along with the presence of a weakly first-order transition, can be attributed to quantum zero-point atomic motion. This zero-point motion smears the free energy landscape of CDW, effectively stabilizing the pristine structure even below the CDW transition temperature. We argue that this surprising behavior could cause coexistence of pristine and CDW structures across the transition and lead to a weak first-order transition. Our predicted lattice dynamical behavior is supported by coherent phonon spectroscopy in single-crystalline CsV₃Sb₅. Our results provide crucial insights into the formation mechanism of CDW materials that exhibit little to no phonon softening, including cuprates, and highlight the surprising role of quantum effects in emergent properties of relatively heavy-element materials like CsV₃Sb₅. 

This work presents the evolution of the electronic properties of kagome superconductor CsV3Sb5 under pressure. The magnetoresistance under high fields of 43 T showed clear Shubnikov–de Haas (SdH) oscillations with multiple frequencies up to 2000 T. With the application of pressure, we observed a sudden change in SdH oscillations with the disappearance of the high-frequency signal near the critical pressure Pc1 ∼ 0.7 GPa. We argue that this change could be due to a reconstruction of the Fermi surface (FS) in CsV3Sb5. To interpret our experimental data, we computed the electronic band structures and FS of CsV3Sb5 using ab initio density functional theory. Our results indicate that both the electronic bands and FS of CsV3Sb5 are highly sensitive to external pressure. The deformation of FS pockets with increasing pressure qualitatively explains our experimental observations. The pressure-driven FS instability in CsV3Sb5 may induce changes in its electronic states, such as superconductivity, charge density wave, nontrivial topology, and more. Therefore, these results are invaluable for gaining insights into these electronic states in CsV3Sb5, as well as in other kagome materials. 

In this work, we study the effect of electron doping on the kagome superconductor CsV₃Sb₅. Single crystals and powders of CsV₃Sb_5−xTe_xare synthesized and characterized via magnetic susceptibility, nuclear quadrupole resonance, and x-ray diffraction measurements, where we observe a slight suppression of the charge density wave transition temperature and superconducting temperature with the introduction of electron dopants. In contrast to hole doping, both transitions survive relatively unperturbed up to the solubility limit of Te within the lattice. A comparison is presented between the electronic phase diagrams of electron- and hole-tuned CsV₃Sb₅.