Magnon Bose Einstein Condensation a brief introduction Dec. 21 st - - PowerPoint PPT Presentation

▶
magnon bose einstein condensation
SMART_READER_LITE
LIVE PREVIEW

Magnon Bose Einstein Condensation a brief introduction Dec. 21 st - - PowerPoint PPT Presentation

Nov 04, 2022 255 likes •630 views

Introduction to Spintronics --- 2018 Fall Magnon Bose Einstein Condensation a brief introduction Dec. 21 st 2018 1 After this presentation, you are supposed to have some basic understanding

slide-1
SLIDE 1

Magnon Bose Einstein Condensation

何梦云 李思衡 李娜 孙慧敏 陈文杰 Introduction to Spintronics --- 2018 Fall

a brief introduction

  • Dec. 21st 2018

1

slide-2
SLIDE 2
  • What is magnon BEC?
  • Why is it so special?
  • How to achieve it?
  • Several experiments.

2

After this presentation, you are supposed to have some basic understanding of:

slide-3
SLIDE 3

Bose Einstein Condensation

3

slide-4
SLIDE 4

Bose Einstein Condensation

If the total particle number N is fixed, the chemical potential has a finite value.

BEC

4

slide-5
SLIDE 5

Bose Einstein Condensation

If the total particle number N is NOT fixed, the chemical potential is always zero!

Why?

5

slide-6
SLIDE 6

Bose Einstein Condensation

6

slide-7
SLIDE 7

Bose Einstein Condensation

If the total particle number N is NOT fixed, the chemical potential is always zero!

no BEC

7

slide-8
SLIDE 8

Magnon

spin wave magnon

(boson s = 1)

8

no BEC

slide-9
SLIDE 9

9

R.I.P. magnon BEC

slide-10
SLIDE 10

Magnon BEC

10

Last hope: raise the chemical potential.

But how?

slide-11
SLIDE 11

Magnon BEC

11

Defined at thermal equilibrium， But at thermal equilibrium … What happens beyond thermal equilibrium?

slide-12
SLIDE 12

Magnon

heating

  • scillating

magnetic field

12

create magnons

cooling dissipation into lattice

destroy magnons scattering

magnon’s life

slide-13
SLIDE 13

Magnon

13

scattering into equilibrium :

  • dissipation into lattice :
  • quasi-equilibrium
slide-14
SLIDE 14

Magnon BEC

14

  • V. E. Demidov et al., Phys. Rev. Lett. 101, 257201 (2008).
  • V. E. Demidov et al., Phys. Rev. Lett.

100, 047205 (2008).

YIG film

slide-15
SLIDE 15

Magnon BEC

15

  • O. Dzyapko et al., Appl. Phys. Lett. 92, 162510 (2008).

YIG film

slide-16
SLIDE 16

Magnon BEC

16

  • O. Dzyapko et al., Appl. Phys. Lett. 92, 162510 (2008).

YIG film

slide-17
SLIDE 17

First experimental discovery of mBEC

17

slide-18
SLIDE 18

Magnon BEC

①microwave electromagnetic field—density of magnon ② > 1, < 100—quasi-equilibrium ③transparent for visible light

18

FM material + + pumping magnons

BEC

= →

slide-19
SLIDE 19

Demokritov S O. et al. Nature, 2006, 443(7110):430-433. Dzyapko O. et al. New Journal of Physics, 2007, 9(3):64.

Experimental set-up

19

Detection: Brillouin light scattering (BLS)

slide-20
SLIDE 20

Dzyapko O. et al. New Journal of Physics, 2007, 9(3):64.

Dispersion curve

  • −
  • 20
slide-21
SLIDE 21

Demokritov S O. et al. Nature, 2006, 443(7110):430-433.

BLS spectrum without pumping

) ( ~ v D

= =

  • − 1
  • − 1

21

slide-22
SLIDE 22

Dzyapko O. et al. New Journal of Physics, 2007, 9(3):64.

BLS spectrum with pumping

22

slide-23
SLIDE 23

300ns

m

Dzyapko O. et al. New Journal of Physics, 2007, 9(3):64.

BLS spectrum with pumping

23

slide-24
SLIDE 24

Demokritov S O. et al. Nature, 2006, 443(7110):430-433.

BLS spectrum with pumping

P=5.9w P=4.0w 0.24 2.4 1.75 0.7

24

slide-25
SLIDE 25

BLS spectrum after pumping

switch-off

Dzyapko O. et al. New Journal of Physics, 2007, 9(3):64.

25

slide-26
SLIDE 26

26

slide-27
SLIDE 27

Research about magnon-magnon interaction

) ( ) ( 4 ) (

2 int

r r g r r m a r r W           

  • Parametric pumping
  • Doubly degenerate mBEC

g>0, repulsive interaction; g<0, attractive interaction

       ) / 2 ( ) / ( ) 2 ( ) 2 (

12 2 1 * 1 12 2 * 2 2 1 2 * 2 12 1 * 1 1

        g g b V b b g V b b g b i b V b b g V b b g b i          

2017

27

slide-28
SLIDE 28

Research about magnon-magnon interaction

kBEC

  • MOKE
  • Wavelength: 490nm
  • Duration: 100 fs
  • Repetition frequency ωL/(2π)=82.379MHz

28

slide-29
SLIDE 29

Research about magnon-magnon interaction

  • H0=113.91kA/m
  • A threshold
  • P<Pth, before the condensation of

magnons

29

slide-30
SLIDE 30

Spin current induced magnons

  • Spin-Hall effect
  • Ferromagnetic Permalloy (Py) strip+Pt
  • Magnetization of Py: 10.2KG
  • Spin current//M
  • Microfocus Brillouin light scattering (BLS)

technique ρ: spectral density of magnons

  • ky=πm/w

2017

) ( ) ( ) (     n D 

30

slide-31
SLIDE 31

Spin current induced magnons

  • H0=200Oe

Oersted field of the current

) ( ) ( ) (     n D  ) ( ) ( ) (    

I I

n D 

thermal equilibrium

31

slide-32
SLIDE 32

Spin current induced magnons

h T T n n R h T k n h T k n

eff I eff B I B

/ ) ( ) ( ) ( /( ) ( / ) (                  ）

  • Teff: frequency

independent scaling

  • f R
  • μ: a comprehensive

modulation on R(ν)

32

slide-33
SLIDE 33

Current induced and detected mBEC

  • Dissipationless magnon transport
  • Idc = 0, nac from the injector decays

exponentially

  • Idc = IBEC, formation of magnon BEC
  • Idc = ISW, magnon damping is

completely compensated

33

slide-34
SLIDE 34

Current induced and detected mBEC

  • µ0H = 50mT, T = 280K
  • =±180 ◦ , magnon accumulation

underneath the modulator

  • =0 ◦, magnon depletion obtained

in this configuration

34

slide-35
SLIDE 35

Current induced and detected mBEC

  • Linear dependence: SHE induced

injection effects

  • Quadratic dependence: thermal

activation

35

slide-36
SLIDE 36

Thank you for your attentions!

36