Inelastic-neutron-scattering study of phonon eigenvectors and frequencies in Si

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Abstract
Longitudinal-acoustic and -optic phonons along the three main symmetry directions in Si were investigated by coherent neutron inelastic scattering. While the determination of phonon frequencies is a routine task, the complementary information on the phonon eigenvectors contained in the intensities of the observed phonon groups is exploited only rarely. The main reasons are problems with correct normalization and reliability of the data, caused by frequent occurrence of spurious peaks. In the present study we addressed this problem by restricting the experiment to scans fulfilling conditions for good resolution so that most of the observed phonon peaks could be resolved from the spurious ones. The inelastic structure factors were then extracted from several sets of integrated intensities, observed at different Q and ω values, and fitted by appropriate models with common scale factors in order to obtain detailed information on eigenvector phases and amplitudes in elliptically polarized modes. The observed eigenvectors and frequencies were found in good agreement with results of ab initio calculations.