Observation of Spontaneous Coherence in Bose-Einstein Condensate of Magnons

Demidov, V. E.; Dzyapko, O.; Demokritov, S. O.; Melkov, G. A.; Slavin, A. N.

doi:10.1103/physrevlett.100.047205

Cited by 141 publications

(185 citation statements)

References 24 publications

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“…[58] is reported by Demidov et al an analysis of the decay, towards final equilibrium, of the NEBEC in YIG, after the external rf-pumping source has been switched off. There are some differences in the experimental protocol with respect to the one used in Ref.…”

Section: Decay Of the Condensatementioning

confidence: 99%

“…[1], but we analyse the decay in the conditions of the latter, to study the dependence (as done in the experiment of Ref. [58]) with the source power.…”

Section: Decay Of the Condensatementioning

confidence: 99%

“…[58]. It consists of three regimes: a near exponential one at the initial delay times (scaled time in the interval 1 to ∼ 1.7 in Fig.…”

Section: The Steady Statementioning

confidence: 99%

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Dynamics of a Bose-Einstein condensate of excited magnons

2013

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Abstract. The emergence of a non-equilibrium Bose-Einstein-like condensation of magnons in rf-pumped magnetic thin films has recently been experimentally observed. We present here a complete theoretical description of the non-equilibrium processes involved. It it demonstrated that the phenomenon is another example of the presence of a Bose-Einstein-like condensation in nonequilibrium many-boson systems embedded in a thermal bath, better referred-to as Fröhlich-Bose-Einstein condensation. The complex behavior emerges after a threshold of the exciting intensity is attained. It is inhibited at higher intensities when the magnon-magnon interaction drives the magnons to internal thermalization. The observed behavior of the relaxation to equilibrium after the end of the pumping pulse is also accounted for and the different processes fully described.

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Section: Decay Of the Condensatementioning

confidence: 99%

“…[1], but we analyse the decay in the conditions of the latter, to study the dependence (as done in the experiment of Ref. [58]) with the source power.…”

Section: Decay Of the Condensatementioning

confidence: 99%

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Dynamics of a Bose-Einstein condensate of excited magnons

2013

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“…These vortex arrays arise without any rotation of the trap, spontaneously breaking rotational symmetry. While much of the possible physics of quantum condensates has been examined in experiments on atomic gases, superfluid Helium and superconductors, there has recently been much interest in examples of condensates of quasiparticle excitations, such as excitons [1,2] (bound electron-hole pairs), exciton-polaritons [3,4,5] (superpositions of quantum well excitons and microcavity photons), and magnons (spin-wave excitations) both in magnetic insulating crystals [6,7] [33] and in superfluid 3 He [8,9,10]. One particular difference shown by these systems is that the quasiparticles have finite lifetimes, and as a result, they can be made to form condensates out of equilibrium, which are best understood as a steady state balance between pumping and decay, rather than true thermal equilibrium.…”

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confidence: 99%

Spontaneous Rotating Vortex Lattices in a Pumped Decaying Condensate

2008

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Injection and decay of particles in an inhomogeneous quantum condensate can significantly change its behaviour. We model trapped, pumped, decaying condensates by a complex Gross-Pitaevskii equation and analyse the density and currents in the steady state. With homogeneous pumping, rotationally symmetric solutions are unstable. Stability may be restored by a finite pumping spot. However if the pumping spot is larger than the Thomas-Fermi cloud radius, then rotationally symmetric solutions are replaced by solutions with spontaneous arrays of vortices. These vortex arrays arise without any rotation of the trap, spontaneously breaking rotational symmetry.PACS numbers: 03.75. Kk,47.37.+q,71.36.+c,71.35.Lk While much of the possible physics of quantum condensates has been examined in experiments on atomic gases, superfluid Helium and superconductors, there has recently been much interest in examples of condensates of quasiparticle excitations, such as excitons [1,2] (bound electron-hole pairs), exciton-polaritons [3,4,5] (superpositions of quantum well excitons and microcavity photons), and magnons (spin-wave excitations) both in magnetic insulating crystals [6,7] [33] and in superfluid 3 He [8,9,10]. One particular difference shown by these systems is that the quasiparticles have finite lifetimes, and as a result, they can be made to form condensates out of equilibrium, which are best understood as a steady state balance between pumping and decay, rather than true thermal equilibrium. The effects of pumping and decay in these condensates have been the subject of several recent works [5,11,12,13,14,15,16,17,18,19,20] which have shown that even when collisions can rapidly thermalise the energy distribution of a system, there may yet be noticeable effects associated with the energy scale introduced by the pumping and decay.The Gross-Pitaevskii equation (GPE) has been applied to successfully describe many features of equilibrium condensates when far in the condensed regime, including density profiles, the dynamics of vortices, hydrodynamic modes -see e.g. [21] and Refs. therein. Using a meanfield description of the condensate, e.g. [18,19,20], one can recover a complex Gross-Pitaevskii equation (cGPE), including terms representing gain, loss and an external trapping potential. This letter studies the interplay between pumping and decay and the external trapping potential in the context of the cGPE in order to illustrate some of the differences between equilibrium and nonequilibrium condensates. In the absence of trapping, this is the celebrated complex Ginzburg-Landau equation that describes a vast variety of phenomena [22] from nonlinear waves to second-order phase transitions, from superconductivity to liquid crystals and cosmic strings and binary fluids [23]. What is of interest in this letter is how pumping and decay, described in the cGPE modify behaviour compared to the regular GPE as is widely applied to spatially inhomogeneous equilibrium quantum condensates [21]. Spatial inhomogeneity, due to either engineere...

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“…The process of magnon relaxation after injection of primary magnons, their thermalization and formation of an overpopulation of the states close to f min is illustrated in figure 7 [17]. The temporal dependences of the BLS intensity from magnons occupying states close to f min are shown for different pumping powers, corresponding to different numbers of magnons injected during the pumping pulse.…”

Section: Bose-einstein Condensationmentioning

confidence: 99%

Bose–Einstein condensation of spin wave quanta at room temperature

Dzyapko

Demidov

Melkov

et al. 2011

Phil. Trans. R. Soc. A.

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Spin waves are delocalized excitations of magnetic media that mainly determine their magnetic dynamics and thermodynamics at temperatures far below the critical one. The quantum-mechanical counterparts of spin waves are magnons, which can be considered as a gas of weakly interacting bosonic quasi-particles. Here, we discuss the roomtemperature kinetics and thermodynamics of the magnon gas in yttrium iron garnet films driven by parametric microwave pumping. We show that for high enough pumping powers, the thermalization of the driven gas results in a quasi-equilibrium state described by Bose-Einstein statistics with a non-zero chemical potential. Further increases of the pumping power cause a Bose-Einstein condensation documented by an observation of the magnon accumulation at the lowest energy level. Using the sensitivity of the Brillouin light scattering spectroscopy to the degree of coherence of the scattering magnons, we confirm the spontaneous emergence of coherence of the magnons accumulated at the bottom of the spectrum, occurring if their density exceeds a critical value.

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Observation of Spontaneous Coherence in Bose-Einstein Condensate of Magnons

Cited by 141 publications

References 24 publications

Dynamics of a Bose-Einstein condensate of excited magnons

Dynamics of a Bose-Einstein condensate of excited magnons

Spontaneous Rotating Vortex Lattices in a Pumped Decaying Condensate

Bose–Einstein condensation of spin wave quanta at room temperature

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