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

Abstract

Uranium is the only element known so far to exhibit a charge-density wave (CDW) instability. The structure below the transition ( T 0 ∼ 43 K) is complex consisting of small displacements of the atoms away from their α-phase equilibrium positions. It is usually assumed that this transition involves a soft phonon condensing at (or near) the CDW position in the Brillouin zone. High-resolution neutron scattering experiments at low temperature show that the principal softening occurs exactly at the CDW positions, as expected for a pure Fermi-surface instability. This result is in agreement with a recent theory which suggests that the CDW-vector components are related to the Fermi-surface nesting topology.