We examine the theory of collisionless transverse current waves in bulk superfluid 3He-B, including the coupling to the order parameter collective modes. At low frequencies, ω << Δ(T), the order parameter modes do not contribute to the restoring force for a transverse current, and the quasiparticle contribution drops rapidly as the gap in the spectrum develops. Thus, low-frequency transverse sound becomes overdamped at temperatures near Tc. However, at low temperatures (T ≈ 0.3 Tc) the off-resonant coupling to the J = 2-, M = ±1 modes stabilizes a propagating transverse current mode, with a large phase velocity and low damping for frequencies above a critical frequency that is approximately that of the J = 2- mode. We also discuss the similarities and differences of longitudinal and transverse sound in the superfluid phases. For example, in zero field right- and left-circularly polarized waves are degenerate. A magnetic field, with H| |q, lifts this degeneracy, giving rise to the analog of circular dichroism and birefringence of electromagnetic waves. Thus, transverse waves may be more easily detected in the B-phase than in normal 3He.
Paper: [PDF] [PS]