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It has been known since the measurement of the phonon modes in the alpha phase of the element uranium (Cmcm orthogonal structure) that the Sigma(4) phonon softens appreciably near the transition to the charge-density wave (CDW) state. In explaining the driving mechanism for the CDW transition, which has 3 components in q-space and occurs at T(CDW)=43 K, Yamada suggested that the most important parameter is q(x) (about 0.5) and that the small q(y) and q(z) components are a consequence of coupling to the strain. Thus, classic soft mode behaviour should be found for the Sigma(4) phonon for T>T(CDW) with its frequency squared being proportional to (T-T(CDW). Experiments on the IN8 triple-axis spectrometer support this idea and show that the frequency does not depend on q(y) or q(z), but they also show that E(2) is proportional to T, which is unusual.

Additional information

Authors: MARMEGGI J C, Université J Fourier, Laboratorie de Cristallographie, Grenoble (FR);CURRAT R, Institut Laue Langevin, Grenoble (FR);ZEYEN C M E, Institut Laue Langevin, Grenoble (FR);LANDER G H, JRC Karlsruhe (DE)
Bibliographic Reference: Paper presented: 1st European Conference on Neutron Scattering, Interlaken (CH), October 8-11, 1996
Availability: Available from (1) as Paper EN 39907 ORA
Record Number: 199611461 / Last updated on: 1997-01-16
Original language: en
Available languages: en