Inertial charge-density-wave dynamics in (TaSe4)2I

Frequency-dependent conductivity measurements are reported in the charge-density-wave (CDW) state of the linear-chain compound (${\mathrm{TaSe}}_4$ ${)}_2$I in the spectral range 4.5–94 GHz. In contrast to other CDW systems which are overdamped, the response is underdamped, with a resonant frequency of approximately 35 GHz, a resonance width of approximately 20 GHz, and an effective mass of ${10}^4$. The large effective mass, large resonant frequency, and small damping are a consequence of the strong electron-phonon coupling in this system.