Theory of neutron scattering from the two-roton, two-maxon and maxon-roton states in superfluid {sup 4}He
- Univ. of Toronto (Canada)
In 1970 Ruvalds and Zawadowski (RZ) outlined a microscopic theory of the two-roton pair excitation spectrum in superfluid {sup 4}He. They pointed out that because of a Bose condensate-induced coupling into the density fluctuation spectrum, these pair excitations show up in inelastic neutron data for S(Q,{omega}) as high energy multiparticle scattering above the maxon-roton quasiparticle peak. Stimulated by recent high-resolution neutron data from ILL, we have carried out an extensive study of the single-particle {rho}{sub 1}(Q,{omega}) and the two-particle {rho}{sub 2}(Q,{omega}) spectral densities within the RZ scenario, over a wide range of wavevectors (1 {approx_lt}Q{approx_lt}3 {angstrom}{sup -1}), frequencies and temperatures. We extend the original RZ analysis (which concentrated on the two-roton spectrum) to include the multiparticle structure associated with the maxon-roton and maxon-maxon spectra and present numerical results for both attractive and repulsive quasiparticle interactions. We also point out that the microscopic theory of S(Q,{omega}), in a Bose-condensed fluid shows that it involves a weighted sum of both {rho}{sub 1}(Q,{omega}) and {rho}{sub 2}(Q,{omega}). As a result, multi-particle structure exhibited by S(Q,{omega}) is not easily related to theoretical results for {rho}{sup 1}(Q,{omega}) and {rho}{sup 2}(Q,{omega}). Previous attempts in the literature to fit neutron data for S(Q,{omega}) to either {rho}{sub 1}(Q,{omega}) or {rho}{sub 2}(Q,{omega}) would not appear to have much quantitative basis, especially in the two-roton frequency region {omega}{approximately}2{Delta}{sub R}.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 98798
- Journal Information:
- Journal of Low Temperature Physics, Vol. 97, Issue 1-2; Other Information: PBD: Oct 1994
- Country of Publication:
- United States
- Language:
- English
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