The dispersion of [sup 3]He quasiparticles in He II from neutron scattering

• Published in: Journal of low temperature physics Vol. 93:1-2
• Main Authors: Scherm, R., Guckelsberger, K., Szprynger, A., Fak, B.
• Format: Journal Article
• Language: English
• Published: United States 01.10.1993
• Subjects: BARYON REACTIONS; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; DISPERSIONS; ENERGY-LEVEL TRANSITIONS; EVEN-EVEN NUCLEI; EVEN-ODD NUCLEI; EXCITATION; FLUIDS; HADRON REACTIONS; HELIUM 3; HELIUM 4; HELIUM II; HELIUM ISOTOPES; HOLES; INELASTIC SCATTERING; ISOTOPES; LIGHT NUCLEI; MIXTURES; NEUTRON REACTIONS; NUCLEAR REACTIONS; NUCLEI; NUCLEON REACTIONS; PHYSICAL PROPERTIES; QUANTUM FLUIDS; QUASI PARTICLES; SCATTERING; SPECIFIC HEAT; STABLE ISOTOPES; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0000-0013 K; TEMPERATURE RANGE 665411 > Basic Superconductivity Studies > (1992-); THERMODYNAMIC PROPERTIES
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/BF00682281

In an inelastic neutron scattering (INS) experiment on [sup 3]He-[sup 4]He mixtures one observes, besides the photon-roton mode which is barely modified by the admixture of [sup 3]He, an additional excitation at lower energies which is interpreted as quasi-particle-hole excitations of a nearly free Fermi gas. The authors reanalyse INS data of x[sub 3] = 1% and 4.5% mixtures at various pressures to extract the mean energy [cflx [omega]][sub q] of the fermions. In the momentum range 9 < q < 17 nm[sup [minus]1] (above 2k[sub F]) [cflx [omega]][sub q] follows very closely the relation [cflx [omega]][sub q] = A[sub 2]q[sup 2] + A[sub 4]q[sup 4] at all concentrations, pressures and temperatures observed. In a 4.5% mixture (T[sub F] [approximately] 0.3 K), measurements were performed for temperatures in the range 0.07 < T < 0.9 K. They find both A[sub 2] and A[sub 4] to be strongly temperature dependent. For the interpretation of thermodynamical properties, the single particle energy [epsilon][sub k] is parametrized as [epsilon][sub k] = [epsilon][sub 0] + 1/(2m[sup *]) [center dot] k[sub 2] [center dot] (1 + [gamma]k[sup 2]). Neglecting interactions between fermions, they calculate from the free-particle [epsilon][sub k] the scattering function S(q,[omega]) and the mean value of the fermion peak energy [omega][sub q] = [integral] [omega]S[sub 3](q,[omega]) d[omega]/[integral]S[sub 3](q,[omega]) d[omega]. They find that [cflx [omega]][sub q] follows closely [epsilon][sub q], deviating at most by 10%. A comparison to the measured A[sub 2] and A[sub 4] directly yields m[sup *](x[sub 3],p,T) and [gamma](x[sub 3],p,T). In the limit x[sub 3] = 0, p = 0, and T = 0, the density and concentration dependence of the inertial mass is in excellent agreement with values found by Sherlock and Edwards. The temperature dependence of the specific heat data from Greywall and Owers-Bradley et al. are well represented by our model at T<0,5 K.