Giant Kohn Anomaly and the Phase Transition in Charge Density WaveZrTe3

Abstract

A strong Kohn anomaly in ${\mathrm{ZrTe}}_3$ is identified in the mostly transverse acoustic phonon branch along the modulation vector $q_P$ with polarization along the $a^{*}$ direction. This soft mode freezes to zero frequency at the transition temperature $T_P$, and the temperature dependence of the frequency is strongly affected by fluctuation effects. Diffuse x-ray scattering of the incommensurate superstructure shows a power-law scaling of the intensity and the correlation length that is compatible with an order parameter of dimension $n=2$.