Phase-channel dynamics reveal the role of impurities and screening in a   quasi-one-dimensional charge-density wave system
  We investigate the low-energy phase excitations of the quasi-one-dimensional charge density wave (CDW) in $\mathrm{K}_{0.3}\mathrm{Mo}\mathrm{O}_3$, by direct probing of infrared-active CDW-lattice modes (phase-phonons) with ultrafast terahertz spectroscopy. Both the nonequilibrium response and temperature dependence of the bands are reconciled by generalizing the time-dependent Ginzburg-Landau theory, beyond that previously applied to the amplitude-phonons, to include impurity effects, while the photoinduced blue-shifts are attributed to a reduction of the electron-phonon coupling induced by a long-lived free-carrier population. 
M. D. Thomson, K. Rabia, F. Meng, M. Bykov, S. van Smaalen, and H. G.   Roskos
cond-mat.mes-hall