Scattering of quasiparticles in $sup 3$He--$sup 4$He mixtures

Journal Article · Mon Oct 01 04:00:00 EDT 1973 · Phys. Rev., A, v. 8, no. 4, pp. 1973-1979

OSTI ID:4344120

Bagchi, A; Ruvalds, J

Considering the elementary excitation spectrum of /sup 3/He -/sup 4/He mixtures to be of the form proposed by Landau and Pomeranchuk, the scattering cross section for roton and /sup 3/He quasiparticle collisions was calculated taking final-state interactions into account. The theory demonstrates the importance of final-state interactions in renormalizing the roton energy and lifetime. Previous theories based on the Porn approximation are shown to give unreliable results for the change of the energy and lifetime for rotons in dilute /sup 3/He --/sup 4/He mixtures owing to roton-/sup 3/He scattering. Upper bound s on the changes in the energy and lifetime of a roton as a function of the roton- /sup 3/He coupling strength were obtained using a simplified model for the coupling. These bounds give an insignificant change of the roton energy with the iHe eoncentration and thus explain recent neutron-seattering and Raman data on the mixtures. Effects of level repulsion between rotons and the /sup 3/He quasiparticle-hole continuum are calculated, and estimated to be small on the basis of recent Raman data, However, decay of a roton into a iHe quasiparticle- hole pair may live rise to an interesting concentration dependence of the roton linewidth. Further experimental studies of the mixtures are suggested, which may check the detailed predictions of the theory and provide insight into the momentum dependence of the coupling parameters. The present analysis represents an essential link between microscopic theories of the quasiparticle coupling and related experiments on dilute /sup 3/He --/sup 4/He mixtures. (auth)

• Research Organization: Univ. of Chicago
• NSA Number: NSA-29-022717
• OSTI ID: 4344120
• Journal Information: Phys. Rev., A, v. 8, no. 4, pp. 1973-1979, Journal Name: Phys. Rev., A, v. 8, no. 4, pp. 1973-1979; ISSN PLRAA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

*HELIUM 3-- QUASI PARTICLES
*HELIUM 4-- QUASI PARTICLES
*QUASI PARTICLES-- SCATTERING
MIXTURES
N66100* --Physics (Low Temperature)--Superfluidity
ROTONS