Magnon BEC in superfluid 3He-A

Bunkov, Yu. M.; Volovik, G. E.

doi:10.1134/s0021364009060101

Cited by 25 publications

(22 citation statements)

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“…The application of an additional magnetic field to this state deflects it from the energy minimum and the condensate may respond by creating collective oscillations known as Goldstone modes. A few different modes of collective oscillations of the HPD have already been observed as torsional oscillations [7,8] and surface oscillations of the free surface of the HPD state [9,10]. This Letter reports the experimental observation of a new (non-)Goldstone mode of the magnon BEC.…”

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confidence: 90%

New Non-Goldstone Collective Mode of BEC of Magnons in SuperfluidHe3−B

Človečko

Gažo²,

Kupka³

et al. 2008

Phys. Rev. Lett.

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Bose-Einstein condensation of magnons in superfluid 3He-B is experimentally manifested by various states where coherent spin precession is established spontaneously, even in nonhomogeneous magnetic fields. Once such a condensate with coherent spin precession is created, it occupies the state with minimal energy, the ground state. The application of an additional magnetic field to that condensate may cause its deflection from the energy minimum and the condensate responds by creating collective gapless oscillations known as Goldstone modes. This Letter reports the experimental observation of a new (non-)Goldstone mode, which can be viewed as an additional NMR mode of condensed magnons in a rotating frame of reference.

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confidence: 90%

New Non-Goldstone Collective Mode of BEC of Magnons in SuperfluidHe3−B

Človečko

Gažo²,

Kupka³

et al. 2008

Phys. Rev. Lett.

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“…This means that the mode II may form the BEC state of magnons [20]. The observed long induction decay after a 120…”

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confidence: 92%

“…For the transverse orientationl ⊥ H one has [20,21]: We have measured the NMR frequency of the induction signal after deflection of magnetization by different angles β in 3 He-B in the radially squeezed aerogel. The experimental results in Fig.…”

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confidence: 99%

Strong Orientational Effect of Stretched Aerogel on theHe3Order Parameter

et al. 2008

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Deformation of aerogel strongly modifies the orientation of the order parameter of superfluid 3 He confined in aerogel. We used a radial squeezing of aerogel to keep the orbital angular momentum of the 3 He Cooper pairs in the plane perpendicular to the magnetic field. We did not find strong evidence for a "polar" phase, with a nodal line along the equator of the Fermi surface, predicted to occur at large radial squeezing. Instead we observed 3 He-A with a clear experimental evidence of the destruction of the long-range order by random anisotropy -the Larkin-Imry-Ma effect. In 3 He-B we observed and identified new modes of NMR, which are impossible to obtain in bulk 3 He-B. One of these modes is characterized by a repulsive interaction between magnons, which is suitable for the magnon Bose-Einstein condensation (BEC). The p-wave superfluid 3 He, which is characterized by an 18-dimensional order parameter, is an amazing test system for different aspects of quantum field theory [1]. Confined in a silica aerogel, superfluid 3 He becomes an ideal system for the investigation of the effect of impurities on a long-range order. In a first approximation the aerogel reduces the superfluid transition temperature [2,3]. Here we report the influence of the aerogel anisotropy on the 3 He order parameter orientation. It was demonstrated earlier that a uniaxial squeezing of a cylindrical aerogel sample leads to the orientation of the orbital momentuml along the cylinder axis [4]. Here we report the first results of experiments with superfluid 3 He whose order parameter is deformed by radially squeezing the aerogel, which is equivalent to uniaxially stretching along the axis of a cylindrical sample. The particular interest for this kind of deformation is due to the prediction of a new phase of superfluid 3 He -the "polar" phase, which has a nodal line in the quasiparticle energy gap in the plane perpendicular to the stretching direction [5]. In our experiments no strong evidence of a polar phase has been found. However, a precursor of a polar phase formation -orientation of the orbital vectorl in the plane of the aerogel squeezing in both 3 He-A and 3 He-B -has been observed.This orientational effect allows us to study the influence of the local random anisotropy of aerogel on the U (1)-field of the vectorl, which is kept in the plane of squeezing. We find that instead of a polar phase, the Imry-Ma state of superfluid 3 He-A is formed. The quenched random anisotropy of the aerogel strands destroys the long-range orientational order (LROO) according to the famous Imry-Ma scenario [6] (see [7,8] and references therein). This is the counterpart of the effect of collective pinning in superconductors predicted by Larkin [9], in which weak impurities destroy the longrange translational order of the Abrikosov vortex lattice.The Larkin-Imry-Ma (LIM) effect has been studied experimentally in 3 He-A confined in a non-deformed aerogel [4,10]. The aerogel diminishes the value of Leggett frequency, which leads to decrease of the frequency s...

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“…The available experimental techniques allow for a control of these quanta population (at least over time scale on the order of seconds) so that the magnon thermalization and formation of BEC are possible. The emerging spin superfluidity manifests itself by coherent transport of the magnetization over macroscopic distances [5].…”

Section: Survey Of the Quantum Superfluidsmentioning

confidence: 99%

On Realization of the Bose-Einstein Condensates and Quantum Superfluids

Domański

2010

Acta Phys. Pol. A

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The purpose of this work is twofold. In the first part we describe superfluidity/superconductivity as an emergent phenomenon resulting from two-body correlations in presence of the Bose-Einstein condensation of particles. We briefly discuss the underlying mechanism for bosons as well as fermion pairs and illustrate various realizations of superfluidity emphasizing the recent examples. In the second part we study the glassy liquid of incoherent pairs which might exist above the transition temperature T c in the underdoped regime of cuprate superconductors. In particular, we explore the angular variation of pseudogap within two-dimensional version of the boson-fermion model using for a quantitative analysis the projective method. We find that above T c the pseudogap closes first near the nodal areas restoring there pieces (arcs) of the Fermi surface whereas remaining parts of the large Fermi surface around the antinodal points are still absent due to incoherent pairs. Upon increasing temperature the length of the Fermi arcs enlarges because the superconducting correlations are gradually suppressed. An intriguing death of Fermi surface can thus be closely related to the Bogoliubov quasiparticles whose existence in the pseudogap state has been predicted by us and confirmed recently by the angle resolved photoemission spectroscopy measurements on Bi PreliminariesQuantum statistical mechanics puts a strong emphasis on the crucial distinction between fermions obeying the Pauli exclusion principle and bosons having no upper bounds for occupying any quantum state at hand. Under specific conditions the latter can macroscopically accommodate in the lowest energy level (for instance in q = 0 momentum of the noninteracting uniform gas or the zero frequency oscillator level E 0 = 1 2 ω for the case of magneto-optically trapped atoms). This phenomenon, referred to as the Bose-Einstein condensation (BEC), has been discovered for the first time in the superfluid state of 4 He. At temperatures far below the lambda transition about 8% of helium atoms gets frozen to the condensate. Recently, the development of trapping and cooling techniques enabled production of the artificial condensates for several atoms. Very dilute densities of the trapped atoms ≈ 10 14 cm −3 require that the quantum degeneracy level is reached at ultracold temperatures, below µK. Such stringent conditions have been so far achieved by a dozen of groups worldwide and the presently available experimental conditions allow for condensation of more than 90% of the trapped atoms [1].A direct realization of BEC among fermions is obviously prohibited. However, an equivalent phenomenon can be obtained in two steps. First, one needs to combine the initial fermions (at least some of their states located near the Fermi level) into the pairs (composite bosons). Depending on specific fermions the possible mechanisms can range from e.g. the phonon mediated pairing in classical superconductors to any other effective attractions -some examples will be discussed in Sect. 2.3. ...

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Magnon BEC in superfluid 3He-A

Cited by 25 publications

References 23 publications

New Non-Goldstone Collective Mode of BEC of Magnons in SuperfluidHe3−B

New Non-Goldstone Collective Mode of BEC of Magnons in SuperfluidHe3−B

Strong Orientational Effect of Stretched Aerogel on theHe3Order Parameter

On Realization of the Bose-Einstein Condensates and Quantum Superfluids

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