In superfluid 3 He-B under conditions of negligible normal fluid density we are able to trap a domain of coherent spin precession away from the destructive influence of boundaries. After the domain is generated by an NMR pulse, the free spin precession may continue for several minutes. Remarkably, we find that these precessing domains may also be generated by cw excitation but only at a frequency considerably higher than that of the precession. We believe that this behavior may indicate that at our temperatures the precessing spin is able to stimulate the orbital moment into sympathetic precession.[S0031-9007 (99)09224-8] PACS numbers: 67.57.Lm, 67.57.Fg, 67.57.JjSuperfluid 3 He has a complex condensate with coherent ordering of the angular momenta and nuclear spins of the Cooper pairs. The coupled orbital and spin motions are both strongly damped by interaction with the normal fluid. Indeed, the orbital viscosity is so large that we can usually take the orbital moment as clamped and regard the condensate nuclear spin system as constituting an independent spin superfluid, the dynamics of which display a very complex range of behavior, readily probed by NMR. However, at the lowest temperatures where the orbital viscosity becomes negligible, there must also appear a similar range of behaviors associated with the orbital fluid. While spin precession is a general feature of magnetic materials, coupled coherent spin precession is a unique feature of the magnetic superfluids. The equivalent orbital motion has no analog in normal materials and is certain to yield as spectacular properties as has the spin superfluid. The search for such new phenomena provides a motive for cooling the superfluid to temperatures where we may be able to see the unfettered behavior of the condensate in all its aspects.With our present cell, we are able to cool the superfluid to temperatures low enough that domains of free coherent spin precession can persist for periods of many minutes [1]. These are the persistent induction signals (PIS) previously observed in 3 He-B at low temperatures [2][3][4][5]. Such domains form after a short NMR excitation pulse. After the pulse scrambles the spin and texture transiently in the experimental region, the long-lived precessional mode then appears as the superfluid attempts to relax to its previous state. In this paper we report that we can also excite these domains continuously by cw excitation. However, the behavior observed is entirely unique in NMR terms; the system responds with a domain precessing at a completely different frequency from that of the excitation. Since something more than just a simple spin fluid is responding here, we believe that these observations may provide the first evidence of orbital precession.The experiments are made in the double cell shown in Fig. 1. The liquid in the inner 5 mm diameter experimental volume can be cooled to 130 mK at zero bar. A steady magnetic field is applied vertically and a field gradient arranged such that the closed base of the cell is normally in l...
Using a ballistic excitation beam generated by a quasiparticle blackbody radiator, we have probed the gap structure of a B-A interface in superfluid 3 He, stabilized magnetically. We see Andreev reflection both from the interface and from the field-distorted B-phase gap. As Andreev processes return excitations to the radiator enclosure, the fraction reflected governs the radiator temperature, from which we infer the maximum spin-dependent quasiparticle gap as a function of magnetic field. These measurements are the first to probe the superfluid 3 He phase interface with quasiparticles.[S0031-9007(96)02033-9] PACS numbers: 67.57. Np, 67.57.Fg, 67.57.Hi Superfluid 3 He shows the highest level of broken symmetry of any ordered condensed matter system. Consequently the superfluid may exist in several phases with different internal structures. The two most common, the A phase and the B phase, have very different order parameters and gap structures. Since these phases may coexist, their phase boundary provides a remarkably unique interface. This is the only such high-symmetry structure between two highly ordered but different Bose condensates to which we have access. Despite the inherent interest, practical difficulties in studying this structure have limited experimental study. The interfacial energy was measured long ago [1]. Various aspects of the interface propagation have been studied [2], but very little else.In this Letter we report the first results of an experiment where we exploit the properties of Andreev reflection to measure the transmission across the B-A phase interface of a quasiparticle beam. The difference in the gap structures of the two phases ensures that at low temperatures ͑kT ø D͒ the available quasiparticle states in the two phases are very different, making quasiparticles ideal probes for observing the interface. We observe very clearly the sudden jump in the gap when the beam is blocked by a region of the A phase via the attendant spectacular fall in the quasiparticle transmission. Further, to demonstrate the quantitative as well as the qualitative possibilities of this method we have also measured the maximum quasiparticle gap as a function of magnetic field, both in the A phase and in the B phase, which we find to be consistent with currently accepted values. At the temperatures of the experiment ͑ഠ120 mK͒ the energy flux emitted in the beam is very sensitive to changes in the excitation gap, a 5% increase in gap yielding a factor of 2 reduction in flux.By directing a thermal beam of excitations through a region of changing gap we can infer the maximum gap height along the path from the fraction Andreev reflected, provided that the excitation mean free paths are long compared with the experimental dimension. Excitations with energies greater than the largest effective gap along the beam path can pass, whereas excitations with smaller energies cannot pass and must be reflected by Andreev processes, which accurately return them back along their previous trajectory.To create a static B-A in...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.