Incommensurate phase associated with the 43 K soft phonon-mode displacive transition in alpha-U

Uranium is the only element known so far to exhibit a charge-density wave ( CDW) instability. The structure below the transition (T-0 similar to 43 K) is complex consisting of small displacements of the atoms away from their a lpha-phase equilibrium positions. It is usually assumed that this transitio n involves a soft phonon condensing at (or near) the CDW position in the Br illouin zone. High-resolution neutron scattering experiments at low tempera ture show that the principal softening occurs exactly at the CDW positions, as expected for a pure Fermi-surface instability. This result is in agreem ent with a recent theory which suggests that the CDW-vector components are related to the Fermi-surface nesting topology . (C) 2000 Elsevier Science B .V. All rights reserved.