NEUTRON SCATTERING FROM QUANTUM LIQUIDS [chapter]

R.A. Cowley
1978 Quantum Liquids  
Recent neutron scattering measurements on the quantum liquids "*He and 3 He are described. In the Bose superfluid there is a well-defined excitation for wave vectors less than 3.6 A"" 1 . In the Fermi liquid measurements are much more difficult because of the large absorption cross section, but measurements at the Institute Laue-Langevin have shown that there are no well-defined excitations at 0.63 K for wave vectors between 1.0 and 2.6 l~l. The difference between these results is due to the
more » ... ts is due to the existence of particle-hole excitations in the Fermi liquid into which collective excitations can decay. Because of the simplicity of the excitations in "*He, it has became a testing ground for the effects of the interactions between the excitations. Measurements are described which show that while rotonroton interactions are attractive at small wave vectors they are repulsive at larger wave vectors. The scattering at large momentum transfer in "*He has been measured, but its interpretation is still open to question.
doi:10.1016/b978-0-444-85117-8.50006-4 fatcat:kltbohlvurhvvfjrmfhytjlzy4