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Abstract:
We discuss order-parameter collective modes in weakly inhomogenous states of superfluid 3He-B,
i.e., states in which the scale of the inhomogeneities is considerably longer than the coherence length,
ξ0 = ℏ vf / 2π Tc, and the energy associated with the
inhomogeneity is small compared to the condensation energy. The theory describes resonance phenomena
between order-parameter modes and zero sound. We discuss two specific cases, both of which involve
excitation of the J = 2+ modes via a parametric field that lifts the selection rule due to
particle-hole symmetry. In the case of a static superflow the modes with
J = 2+, M = ± 1 couple to sound for q || H, and should be observable
as Zeeman states with a maximum absorption that scales as the square of the superflow velocity.
The J = 2+ modes may also be excited parametrically in a three-wave resonance process
involving two zero-sound phonons. We summarize the nonlinear response theory for two-photon excitation
of these modes.
† Invited Paper for the Proceedings of the 19th International Conference on Low Temperature Physics, Brighton, UK.
Paper: [PDF]
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