Observation of a Charge-Density Wave inα-U at Low Temperature

The discovery of a charge-density wave (CDW) in $\alpha$-U at ∼43 K is reported. The mode corresponds to the condensation of a longitudinal-optic phonon near $\overrightarrow{\mathrm{q}}=[\frac{1}{2}, 0, 0]$ in which the atoms are displaced by ∼0.006 ÅA from their special positions. Large precursor effects are seen in the phonon spectra. The wave vector of the CDW is related to that of the fundamental lattice in a rather complex way, which is discussed in terms of discommensurations between the CDW (${\alpha }^{\prime }$ phase) and the primary $\alpha$ phase.