Single Particle and Collective Excitations in the One-Dimensional Charge Density Wave SolidK0.3MoO3Probed in Real Time by Femtosecond Spectroscopy

Ultrafast transient reflectivity changes caused by collective and single particle excitations in the quasi-one-dimensional charge-density wave (CDW) semiconductor ${\mathrm{K}}_{0.3}{\mathrm{MoO}}_3$ are investigated with optical pump-probe spectroscopy. The temperature dependence of nonequilibrium single particle excitations across the CDW gap and their recombination dynamics are reported for the first time. In addition, amplitude mode reflectivity oscillations are observed in real time. A $T$-dependent overdamped response is also observed which is attributed to relaxation of the phason mode.