Interplay of nanoscale strain and smectic susceptibility in kagome superconductors

Exotic quantum solids can host rotation symmetry breaking states 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 AV₃Sb₅ using spectroscopic-imaging scanning tunneling microscopy (SI-STM). We discover local decoupling between the smectic electronic director axis and the direction of anisotropic strain.. This decoupling tends to occur in regions where the CDW gap is the largest. This suggests nanoscale variations in smectic susceptibility. Overall, our observation of weak smecto-elastic coupling in the CDW phase of kagome superconductors is phenomenologically different from the nemato-elastic coupling in the Ising nematic phase of Fe-based superconductors, providing a contrasting picture of how strain can control electronic unidirectionality in different families of quantum materials.