Spin superfluidity and magnon Spin superfluidity and magnon Bose – Bose – Einstein condensation Einstein condensation MicroKelvin, 2013 Yuriy Bunkov Yuriy Bunkov Institute Neel, CNRS, Grenoble, France Institute Neel, CNRS, Grenoble, France 1. Review of Magnon BEC 2. Saga de Persistent signal
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Spin superfluidity and magnon Bose – Einstein condensation MicroKelvin, 2013 Yuriy Bunkov Institute Neel, CNRS, Grenoble, France 1. Review of Magnon BEC.
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Spin superfluidity and magnon Bose – Spin superfluidity and magnon Bose – Einstein condensationEinstein condensation
1. Field induced magnetic phase transition as a magnon Bose Einstein condensation
No, System in thermal equilibrium can not create the BEC state
2. Magnetic transport in a superfluid vacuum
No, This is the property of vacuum, the superfluid state of 3He.It is a property of texture, not particles.
What we will not speak about:
And we will speak about of magnonsBEC and magnons spin supercurrent, notDirectly connected with mass superfluidity
Superfluid 3HeQuantum vacuumcharacterized by
phase S (magnetization) L (orbital momentum)
Quasiparticles
Magnons
Acoustic modes
Topological defects:
Boojum
Vortex
Brane
Particles:
Fields:
Texture of orbital momentum
Holstain-Primakoff transformation
0
0.2
0.4
0.6
0.8
1
0
0.5
1
1.5
2
2.5
3
0 0.1 0.2 0.3 0.4 0.5Time, s.
Signal in the time domainA
B
0 100 200 300 400 500 600
0s.0.02s0.2s0.4s0.3s
Frequency shift, Hz.
Magnons destribution
0.03 s after the pulsebroadening 0.5 Hz
0.2 s after the pulsebroadening 2 Hz
0.3 s after the pulse( 2 Hz )
0.4 s after the pulse( 2 Hz )
Grenoble, 2003
Spin superfluidity and BEC of magnons was found in a 5 different states of superfluid 3He. In one of this states the induction signal can live more then one hours. Its corresponds to a 99.999% of magnons to be condensed! For an atomic BEC the 30% condensation was only achieved!
Magnon BEC Atomic BEC
Ideal gas
Quantum gas
BEC, superfluidity
Paramagnetic, Fermi liquid
Magnetically ordered
Coherent precession
H
H
H
Sx + iSy = S sin e it +i
=Hloc
=
2. Thermalized magnons = 0No BEC
1. Trap. It may be space trap (as for particle BEC) or even the trap of energy of magnons interactionH
S
2. Small angle of deflection
H
S
Not enough for BEC
For superfluid 3He critical angle is about 0.20
1. Trap. It may be space trap (as for particle BEC) or even the trap of energy of magnons interaction
2. Big angle of deflection H
SEnough for BEC but
Attractive interaction leads to instability of coherent precession. NO BEC
2. Big angle of deflection
1. Trap.
H
S
Repulsive interaction !BEC ?
May be NOT! If magnons live too short timeExample – stationary spin waves.
The important is the spontanuos simmetry breaking.How to check? 1.Long induction decay, longer then the inhomogeneity of magnetic field 2. Non-resonance excitation (In frequency or in place)
H
CW NMRrf
= 0
x
Hx
The magnetic relaxation leads to decrease of BEC region
Minimization of energy in the conditions of magnetization Conservation and the gradient of chemical potencial
It can be compensated by a small resonance RF pumping
HPD1
20
JETPh Letters, v.47, p.478, (1988).
JosephsonJosephson
HPD 2
HPD 2
AerogelStycast
F
P Hunger, Yu M Bunkov, E Collin, and H Godfrin Journal of Physics: Conference Series. 400 012019 (2012)
Yu. M. Bunkov, E. M. Alakshin, R. R. Gazizulin, A.V. Klochkov, V.V. Kuzmin, V.S. L'vov, and M.S. Tagirov. “High Tc spin superfluidity in antiferromagnets”, Phys. Rev. Lett. 108, 177002 (2012).