Experimental study of a non-pair inter-ion interaction through conduction electrons in aluminium

The method of neutron inelastic scattering in a triple-axis spectrometer was used to study an isolated singularity on the transverse phonon branch in the (100) direction of an Al single crystal in the neighbourhood of wave vector q/qsub(max) approximately 0.42. The purpose of the study was to identify the singularity as being three-particle in nature, i.e. associated with the occurrence of unpaired inter-ion interaction, unlike the Kohn anomaly (q/qsub(max) approximately 0.76) observed on the same branch. Phonon measurements (delta ω/delta q vector) were carried out both in the (100) and in the (10xi) direction (xi=0.176, which corresponds to an inclination of 100 to the (100) direction), while in the non-symmetrical direction delta ω/delta q vector was measured for phonons of different polarization. It was found that in the (10xi) direction there is a 'splitting' of the singularities, the character and polarization dependence of which process indicate that for q/qsub(max) approximately 0.42 the singularity is a three-particle one. (author)