Optical response of the sliding charge density wave in K _0.3MoO ₃

Abstract
We measured the optical response of K _0.3MoO ₃ along the b-axis in the CDW ground state and found two optical modes in the millimeter wave and far-infrared range which we assign to the amplitude and the phason mode located at 2 cm ^-1 and 10 cm ^-1 respectively. Applying an external electric field, which exceeds the threshold of non-linear conductivity, an new mode appears around 4 cm ^-1 which exhibits an additional fine structure. Ths mode may be related to the sliding charge density condensate which interacts with the underlying lattice. We observe no change in the phason mode under bias and only a small loss of spectral weight in the amplitude mode.