Response Functions and Collective Excitations of HELIUM-3 in a Magnetic Field
This thesis studies the magnetic response of ('3)He on two energy scales: the Fermi energy (epsilon)(,F) in the normal state and the binding energy of Cooper pairs 2(DELTA) in the superfluid. In the normal state, we find that the coupling between zero sound and longitudinal spin oscillations is proportional to (gamma)H/(epsilon)(,F), which is of order 10('-3) for a 10 kG field. The superfluid is much more sensitive to a magnetic field because the S(,z) = (+OR-)1 and S(,z) = 0 Cooper pair populations shift when (gamma)H becomes comparable to (DELTA) (TURNEQ) 10(' -3)(epsilon)(,F). Using mean field theory and an expansion in (gamma)H/(DELTA), we study the response of the B phase to a magnetic field (')H = Hz. While depleting the S(,z) = 0 Cooper pair population, the magnetic field compresses the l = 1 gap and generates a l = 3 gap. These effects contribute to the enhancement of the magnetic susceptibility and to the nonlinear field splitting and dispersion of the real squashing modes. The dipole interaction distorts the B phase gap even in the absence of a magnetic field. When the z component of the l = 1 gap vanishes, ('3)He makes a second order phase transition into a rotated planar state. We include l = 3 correlations and nonquasiparticle corrections in a calculation of the field dependence of the Leggett angle and of the longitudinal spin wave frequency in the collisionless regime. In the absence of the dipole interaction, Fermi liquid corrections shift the longitudinal spin wave frequency in a finite field. To determine the Fermi liquid and pairing interactions that parametrize the quasi-particle vertex, we compare our results with the susceptibility data of Hoyt et al and the real squashing mode data of Shivaram et al.
- Pub Date:
- Physics: Condensed Matter