ANHARMONIC DYNAMICAL BEHAVIOR IN BCC ZIRCONIUM

We present inelastic neutron scattering measurements of the low energy and strongly damped phonons in the high temperature bcc phase of zirc onium. These phonons were investigated at different scattering vectors Q but equivalent phonon wave vectors q in different Brillouin zones o r along different but equivalent paths in the same Brillouin zone. Nei ther the observed differences in intensity nor in line shapes can be e xplained by the coherent one-phonon scattering law S-1(Q,omega). This leads to an apparent violation of the fundamental symmetry of lattice dynamics. Taking into account the strong anharmonicity of these phonon s, interferences between one- and multi-phonon scattering are held res ponsible for these effects. Measurements in different scattering plane s reveal that due to the symmetry of the bcc lattice, these effects ca n only be observed in certain directions.