Emergent symmetry in TbTe₃revealed by ultrafast reflectivity under anisotropic strain

We report ultrafast reflectivity measurements of the dynamics of the order parameter of the charge density wave (CDW) in TbTe₃under anisotropic strain. We observe an increase in the frequency of the amplitude mode with increasing tensile strain along thea-axis (which drives the lattice intoa > c, withaandcthe lattice constants), and similar behavior for tensile strain alongc(c > a). This suggests that both strains stabilize the corresponding CDW order and further support the near equivalence of the CDW phases oriented ina- andc-axis, in spite of the orthorhombic space group. The results were analyzed within the time-dependent Ginzburg-Landau framework, which agrees well with the reflectivity dynamics. Our study presents an ultrafast approach to assess the stability of phases and order parameter dynamics in strained systems.