Spin currents in superfluid 3He

Фомин, И. А.

doi:10.1016/0921-4526(91)90222-z

Cited by 22 publications

(29 citation statements)

References 12 publications

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“…The energy of the spin-current state with a vortex and the energy of the barrier, which blocks the phase slip, i.e., the decay of the current, are determined similarly to the case of mass superfluidity [see equations (12) and (13)]:…”

Section: Stability Of Spin-current Statesmentioning

confidence: 99%

“…The final goal of spintronics is to create devices based on spin manipulation, and transport of spin with minimal losses is crucial for this goal. Now one can find reviews summarizing the investigations done during the first [11] and the second [12,13] periods of works on dissipationless spin transport. On the other hand, the work on spin transport in spintronics is a developing story, and probably it is still premature to write summarizing reviews.…”

Section: Introductionmentioning

confidence: 99%

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Spin currents and spin superfluidity

Sonin

2010

Advances in Physics

240

300

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The present review analyzes and compares various types of dissipationless spin transport: (1) Superfluid transport, when the spin-current state is a metastable state (a local but not the absolute minimum in the parameter space). (2) Ballistic spin transport, when spin is transported without losses simply because sources of dissipation are very weak. (3) Equilibrium spin currents, i.e., genuine persistent currents. (4) Spin currents in the spin Hall effect. Since superfluidity is frequently connected with Bose condensation, recent debates about magnon Bose condensation are also reviewed. For any type of spin currents simplest models were chosen for discussion in order to concentrate on concepts rather than details of numerous models. The various hurdles on the way of using the concept of spin current (absence of the spin-conservation law, ambiguity of spin current definition, etc.) were analyzed. The final conclusion is that the spin-current concept can be developed in a fully consistent manner, and is a useful language for description of various phenomena in spin dynamics.

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Section: Stability Of Spin-current Statesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spin currents and spin superfluidity

Sonin

2010

Advances in Physics

240

300

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“…In 3 He-B, the magnon BEC is represented by a domain with a fully phase-coherent precession of magnetization, known as the Homogeneously Precessing Domain (HPD). HPD exhibits all the properties of spin superfluidity (see Reviews [10,11,12]). These include in particular: spin supercurrent which transports the magnetization; spin current Josephson effect and phase-slip processes at the critical current; and spin current vor-1…”

mentioning

confidence: 99%

“…However, under special conditions, when 3 He-A is confined in the properly deformed aerogel, interaction between magnons becomes repulsive and a stable Bose condensate is formed. The magnon BEC is described in terms of complex order parameter Ψ, which is related to the precessing spin in the following way [10,11]:…”

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confidence: 99%

Magnon BEC in superfluid 3He-A

Bunkov

Volovik²

2009

Jetp Lett.

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The new mode of magnetization precession in superfluid 3 He-A in a squeezed aerogel has been recently reported. We consider this mode in terms of the Bose-Einstein condensation (BEC) of magnons. The difference between magnon BEC states in 3 He-A and in 3 He-B is discussed. PACS:The discovery [1] and detailed investigations of the phase-coherent precession of magnetization in superfluid 3 He-B generated a search for similar phenomena in other systems. Superfluid 3 He-A could be a proper system. However, it was found that under typical conditions the coherent precession in 3 He-A is unstable [2] because of the convex shape of spin-orbit energy potential as function of magnetization [3,4]. It was suggested that the shape of potential can be inverted and thus the coherent precession can be stabilized if the orbital momentum of Cooper pairs in 3 He-A is oriented along the applied magnetic field [5]. Recently such orientation has been reached for 3 He-A immersed in the axially squeezed aerogel [6], and the first experiments with the coherently precessing state (CPS) of magnetization have been reported [7]. Here we discuss the phenomenon of the coherent precession of magnetization in superfluid 3 He-A in terms of the Bose-Einstein condensation (BEC) of magnons, and consider the difference between magnon BEC states in 3 He-A (CPS) and in 3 He-B (HPD). BEC is one of the most remarkable quantum phenomena. It corresponds to formation of collective quantum state, in which the macroscopic number of particles is governed by a single wave function. The formation of Bose-Einstein condensate was predicted by Einstein in 1925, for review see e.g. [8]. The almost perfect BEC state was observed in ultra could atomic gases. In Bose liquids, the BEC is strongly modified by interactions, but still remains the key mechanism for formation of coherent quantum state, which experiences the phenomenon of superfluidity: nondissipative superfluid current. In liquid 4 He the depletion of the condensate is very large: in the limit of zero temperature only about 10% of particles occupy the state with zero momentum. Nevertheless the whole liquid (100% of atoms) forms the 1) yuriy.bunkov@grenoble.cnrs.fr; volovik@boojum.hut.fi coherent quantum state at T = 0, so that the superfluid density equals the total density, ρ s (T = 0) = ρ. The latter is valid for any monoatomic superfluid system with translational invariance, including superfluid 3 He with the non BEC mechanism of coherent quantum state. If translational invariance is violated by impurities, crystal fields or other inhomogeneity, the superfluid component is suppressed:Superfluidity is a very general quantum property of matter at low temperatures, with variety of possible nondissipative superfluid currents, such as supercurrent of electric charge in superconductors; hypercharge supercurrent in the vacuum of Standard Model; supercurrent of color charge in a dense quark matter; etc. The origin of superfluidity is the spontaneous violation of the U (1) symmetry related to the conservation of ...

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“…Similar to the conventional mass superfluidity which also experiences the off-diagonal long-range order, the spin precession in Eq. (1) can be rewritten in terms of the complex scalar order parameter [7,9,10] …”

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confidence: 99%

Spin vortex in magnon BEC of superfluid 3He–B

Bunkov

Volovik

2008

Physica C: Superconductivity and its Applications

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The phenomenon of the spontaneous phase-coherent precession of magnetization in superfluid 3 He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different magnon BEC states have been observed: homogeneously precessing domain (HPD); BEC condensation in the spin-orbit potential trap (Q-balls); coherent precession with fractional magnetization; and two modes of the coherent precession in squeezed aerogel. The spin superfluidity effects, like spin Josephson phenomena, spin current vortices, spin phase slippage, long distance magnetization transport by spin supercurrents have been observed. The almost perfect BEC state was observed in ultra could atomic gases. In Bose liquids, the BEC is strongly modified by interactions, but still remains the key mechanism for the formation of a coherent quantum state in Bose systems, which exhibits the phenomenon of superfluidity characterized by nondissipative superfluid mass currents discovered first in 4 He by P.L. Kapitza [2]. Superfluidity proved to be a more general phenomenon: superfluid mass current has been found in Fermi liquid 3 He; superfluidity of electric charge -superconductivityis known in metals; superfluidity of chiral charge is discussed in quantum chromodynamics; color superfluidity -in quark matter and baryonic superfluidity -in neutron stars; etc. Here we discuss magnon BEC with spin current superfluidity.Strictly speaking, the theory of superfluidity and Bose-Einstein condensation is applicable to systems with conserved U (1) charge or particle number. However, it can be extended to systems with a weakly violated conservation: it can be applicable to a system of sufficiently long-lived quasiparticles -discrete quanta of energy that can be treated as condensed matter counterpart of elementary particles. In magnetically ordered materials, the corresponding propagating excitations are magnonsquanta of spin waves. Under stationary conditions the density of thermal magnons is small, but they can be pumped by resonance radio-frequency (RF) field (magnetic resonance). One may expect that at very low temperatures, the non-equilibrium gas of magnons could live a relatively long time, sufficient for formation of coherent magnon condensate.Recently there appeared a number of articles, where authors claimed the observation of BEC of quasiparticles: excitons [3] and magnons [4]. To

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Spin currents in superfluid 3He

Cited by 22 publications

References 12 publications

Spin currents and spin superfluidity

Spin currents and spin superfluidity

Magnon BEC in superfluid 3He-A

Spin vortex in magnon BEC of superfluid 3He–B

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