Abstract: Second-order Raman scattering from solid argon at low temperature exhibits sharp features corresponding to van Hove singularities arising from critical points in the joint phonon density of states. The singularities observed in a crystal grown at 10 kbar compare favorably with those calculated at a lower density after the frequencies are scaled. Comparison of the calculated relative intensities of these features with those observed shows that the coupling between pairs of longitudinal phonons has been underestimated while the coupling between phonons of different branches has been exaggerated. The variation of spectral intensity and shape measured from low temperature (12 K) to near melting (256 K) can be attributed to the changing occupation numbers of the phonon pairs and smoothing of the joint density of states as the temperature rises. In addition, an average mode Gruneisen parameter of value 2.67 was measured relative to a crystal grown at 5 kbar.
Rct Date:(Received 14 August 1987)
PACS:Type: E-T-Experimental-Theoretical. Year: 88. Class nos. 63.20.-e; 78.30.-j
CPM no.: Microfilm no(s): 8802B2007 Abstract no(s): 1.04598
Keywords:Number: 15. ARGON :T1; SOLIDS; VERY HIGH PRESSURE; ULTRALOW TEMPERATURE; VERY LOW TEMPERATURE; LOW TEMPERATURE; RAMAN SPECTRA :Q1; VAN HOVE THEORY; SINGULARITY; PHONONS; ENERGY-LEVEL DENSITY; LINE SHAPE; AMPLITUDES; TEMPERATURE DEPENDENCE; LASER RADIATION