Two Roton Raman Scattering in Superfluid He4
The possibility of using Raman scattering as a probe for studying the elementary excitations of superfluid helium was first suggested by Halley1 in 1968. Raman scattering in helium is a second order process in which two excitations of nearly equal and opposite momenta are created in the liquid. The spectrum of scattered light at an energy loss E is a measure of the density of two excitation states with zero total wavevector and energy E.1,2 The primary contribution comes from the roton region of the dispersion curve. At low temperatures this consists of a well defined line near E = 2Δ, where Δ is the energy of the roton minimum. I will concentrate on the 2-roton light scattering. A discussion of the spectrum in other energy regions can be found in reference 3.
KeywordsDispersion Curve Line Shape Saturated Vapor Pressure Energy Shift Cutoff Function
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