Collisionless collective modes in superfluid 3He (original) (raw)
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Collective Modes and f-Wave Pairing Interactions in Superfluid He3
Physical Review Letters, 2006
Precision measurements of collective mode frequencies in superfluid 3 He-B are sensitive to quasiparticle and f -wave pairing interactions. Measurements were performed at various pressures using interference of transverse sound in an acoustic cavity. We fit the measured collective mode frequencies, which depend on the strength of f -wave pairing and the Fermi liquid parameter F s 2 , to theoretical predictions and discuss what implications these values have for observing new order parameter collective modes.
Dispersion induced splitting of the collective mode spectrum in A-phase of superfluid 3He
Physics Letters A, 2009
The whole collective mode spectrum in axial and planar phases of superfluid 3 He with dispersion corrections is calculated for the first time. In axial A-phase the degeneracy of clapping modes depends on the direction of the collective mode momentum k with respect to the vector l (mutual orbital moment of Cooper pairs), namely: the mode degeneracy remains the same as in case of zero momentum k for k l only. For any other directions there is a threefold splitting of these modes, which reaches maximum for k⊥l.
Journal of Low Temperature Physics, 2009
The whole collective mode spectrum in axial and planar phases of superfluid 3He with dispersion corrections is calculated for the first time. In axial A-phase the degeneracy of clapping modes depends on the direction of the collective mode momentum k with respect to the vector l (mutual orbital moment of Cooper pairs), namely: the mode degeneracy remains the same as in case of zero momentum k for k‖l only. For any other directions there is a threefold splitting of these modes, which reaches maximum for k ⊥ l. In planar 2D-phase, which exists in the magnetic field (at H>H C ) we find that for clapping modes the degeneracy depends on the direction of the collective mode momentum k with respect to the external magnetic field H, namely: the mode degeneracy remains the same as in case of zero momentum k for k‖H only. For any other directions different from this one (for example, for k ⊥ H) there is twofold splitting of these modes. The obtained results imply that new interesting features can be observed in ultrasound experiments in axial and planar phases: the change of the number of peaks in ultrasound absorption into clapping mode. One peak, observed for these modes by Ling et al. (J. Low Temp. Phys. 78:187, 1990), will split into two peaks in a planar phase and into three peaks in an axial phase under the change of ultrasound direction with respect to the external magnetic field H in a planar phase and with respect to the vector l in an axial phase. In planar phase, some Goldstone modes in the magnetic field become massive (quasi-Goldstone) and have a similar twofold splitting under the change of ultrasound direction with respect to the external magnetic field H. The obtained results as well will be useful under interpretation of the ultrasound experiments in axial and planar phases of superfluid 3He.
Modes of superfluid 3He in the entire hydrodynamic region
Physica B: Condensed Matter, 1990
Dispersion relations for hydrodynamic modes are normally derived in the limit of small damping. This limit covers the entire hydrodynamic region as long as the region conincides with the small damping region (e.g., in 4He-II). This is not the case in superfluid 3He. In this paper the dispersion relations of second sound and sq-mode are generalized throughout the hydrodynamic region. It might have experimental implications for any 3He experiment dealing with frequencies of Hz and higher. They are discussed in detail.
Discovery of an excited pair state in superfluid 3He
Nature Physics, 2008
Order parameter collective modes are the fingerprint of a condensed phase. The spectroscopy of these modes in superfluid 3 He and unconventional superconductors can provide key information on the symmetry of the condensate as well as the microscopic pairing mechanism responsible for the ground state and excitation energies. We report the discovery of a new collective mode in superfluid 3 He-B which we identify as an excited bound state of Cooper pairs. We use interferometry within an acoustic cavity that is very sensitive to changes in the velocity of transverse sound. Our measurements of sound velocity and mode frequency, together with the observation of acoustic birefringence indicate that this new mode is weakly bound with an excitation energy within 1% of the pair-breaking edge of 2∆. Based on the selection rules for coupling of transverse sound to a collective mode in 3 He-B, combined with the observation of acoustic birefringence near the collective mode frequency, we infer that the new mode is most likely a spin-triplet (S = 1), f -wave pair exciton (L = 3) with total angular momentum, J = 4. The existence of a pair exciton with J = 4 suggests an attractive, sub-dominant, f -wave pairing interaction in liquid 3 He.
Low energy dynamics of gapless and quasi-gapless modes of vortices in superfluid 3^33He-B
We discuss the low energy effective dynamics of gapless excitations of the mass vortices of systems similar to the Ginzburg-Landau description of superfluid helium-3 in the bulk B phase. Our approach is to determine the vortex solution by considering a specific ansatz for the order parameter and minimizing the free energy. The conditions on the β i coefficients required for the stability of the various solutions for the order parameter are calculated. By considering the symmetries that are broken by the vortex solutions we are able to generate the moduli fields associated with the low energy excitations of the vortices. Using these fields we determine the effective free energy describing the dynamics of these excitations.
Non-Abelian quasigapless modes localized on mass vortices in superfluid ^{3}He-B
Physical Review D, 2013
Kelvin waves, or Kelvons, have been known for a long time as gapless excitations propagating along superfluid vortices. These modes can be interpreted as the Nambu-Goldstone excitations arising from the spontaneous breaking of the translational symmetry. Recently a different type of gapless excitation localized on strings -the so-called non-Abelian mode -attracted much attention in high-energy physics. We discuss their relevance in condensed matter physics. Non-Abelian rotational quasigapless excitations could appear on the mass vortices in the B phase of the superfluid 3 He, due to the fact that the order parameter in 3 He-B is tensorial. While the U(1) rotational excitations are well established in vortices with asymmetric cores, the non-Abelian rotational excitations belonging to the same family were not considered.
Broken relative symmetry and the hydrodynamics of superfluid 3He
Physica B+C, 1982
Macroscopic condensed systems sometimes break various continuous symmetries in such a way that they remain invariant under the transformations given by certain combinations of these symmetries. This instance, the breaking of a relative symmetry, is discussed in detail. A system of broken relative symmetry is shown to behave as if it broke all the constituent symmetries but lacked the capability to distinguish between them. Each of the three superfluid phases of 'He breaks a relative symmetry not encountered in any other known condensed system. Hence each of them is the only representative in nature of a characteristic hydrodynamic response. These symmetries are specified and the corresponding hydrodynamics discussed. In addition, recent work on 3He dynamics and related problems, especially the peculiar thermodynamic properties of 3He, rotating in equilibrium, are reviewed
Physical Review B, 2004
The signature of superfluidity in bosonic systems is a sound wave-like spectrum of the single particle excitations which in the case of strong interactions is roughly temperature independent. In fermionic systems, where fermion pairing arises as a resonance phenomenon between free fermions and paired fermionic states (examples are: the atomic gases of 6 Li or 40 K controlled by a Feshbach resonance, polaronic systems in the intermediary coupling regime, d-wave hole pairing in the strongly correlated Hubbard system), remnants of such superfluid characteristics are expected to be visible in the normal state. The single particle excitations maintain there a sound wave like structure for wave vectors above a certain qmin(T) where they practically coincide there with the spectrum of the superfluid phase for T < Tc. Upon approaching the transition from above this region in q-space extends down to small momenta, except for a narrow region around q = 0 where such modes change into damped free particle like excitations.
Theory of pair breaking by vibrating macroscopic objects in superfluid 3He
Physica B: Condensed Matter
An intuitive picture of dissipation through pair breaking by macroscopic, vibrating objects in an isotropic superfluid is presented, which predicts a critical velocity for direct quasi-particle emission of v c = v0/(1 + ~), where v 0 is the Landau velocity and a characterizes the superfluid backflow. A new intermediate frequency regime is identified, in which pulsed experiments should reveal a hierarchy of critical velocities and sinusoidally vibrating objects will exhibit a crossover to diffusive behaviour. A model of flow through a channel with a rough surface is analyzed, which yields for the instantaneous dissipation Q-(v-vc) 5 and Q ,~ v 2, at low and high velocities, respectively.