in a room-temperature magnon Bose-Einstein condensate Oleksandr - - PowerPoint PPT Presentation

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Spin transport by a supercurrent in a room-temperature magnon Bose-Einstein condensate

Fachbereich Physik and Landesforschungszentrum OPTIMAS Technische Universität Kaiserslautern Germany

Oleksandr Serha (Alexander A. Serga)

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Kaiserslautern University

Frankfurt

Kaiserslautern

Munich Berlin Hamburg Amsterdam Paris Brussels Stuttgart London

City in the State of Rhineland-Palatinate (Rheinland-Pfalz)

Munich Berlin Frankfurt Hamburg Stuttgart

Kaiserslautern

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Kaiserslautern University

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

AG Magnetismus

• Jun. Prof. Dr. E. Th. Papaioannou, Dr. P. Pirro, V. Lauer, Dr. B. Leven, T. Fischer,
• T. Langner, Dr. D. Passarello, M. Kewenig, P. Jaeger, L. Mihalceanu, T. Noack, H. Schäfer,
• B. Heinz, D. A. Bozhko, Dr. P. Clausen, M. Schneider, M. Geilen, Dr. habil. A. A. Serga,
• S. Keller, M. Schweizer, Dr. V. I. Vasyuchka, Prof. Dr. B. Hillebrands, T. Meyer,
• Dr. A. Conca Parra, F. Heussner

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Concept of magnon spintronics

A.V. Chumak, V.I. Vasyuchka, A.A. Serga, B. Hillebrands, Magnon spintronics, Nat. Phys. 11, 453 (2015)

Magnon transport plays a central role in magnonics

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

PERFORMANCE

Computing principles Computing principles

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

PERFORMANCE

Computing principles Computing principles

Macroscopic quantum states and magnon supercurrents

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

University of Kaiserslautern (Germany)

Collaborators

Magnon-supercurrent-team

Alexander Kreil Halyna Musiienko-Shmarova Laura Mihalceanu Timo Noack Dmytro Bozhko Vitaliy Vasyuchka Burkard Hillebrands Oleksandr Serha Pascal Frey

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Gennadii Melkov

Taras Shevchenko National University of Kyiv (Ukraine)

Collaborators

External collaborators

Weizmann Institute of Science (Israel)

Victor L'vov Anna Pomyalov

Oakland University (USA)

Andrey Slavin Vasyl Tiberkevich

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Experimental and theoretical inspiration

• f supercurrents studies

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnons

q 

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon gas

• Energy
• Momentum
• Mass
• Spin
• Four- and three-magnon scattering

Magnon as a quanta of spin-wave

1 s 

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon gas

 Linear process  Nonlinear processes

e1, p1 e2, p2 e3, p3 e4, p4

Four-magnon scattering

e1, p1 e1, p2

Two-magnon scattering

e1, p1 e2, p2 e3, p3 e1, p1 e2, p2 e3, p3

Three-magnon decay Three-magnon confluence

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon gas

 Linear process  Nonlinear processes

e1, p1 e2, p2 e3, p3 e4, p4

Four-magnon scattering

e1, p1 e1, p2

Two-magnon scattering

e1, p1 e2, p2 e3, p3 e1, p1 e2, p2 e3, p3

Three-magnon decay Three-magnon confluence

Gas of interacting magnetic quasiparticles Number of quasiparticles is conserved

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Yttrium Iron Garnet Y3Fe5O12 (YIG)

• V. Cherepanov, I. Kolokolov, and V. L’vov, The saga of YIG:

spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet, Phys. Rep. 229, 81–144 (1993).

“Yttrium-Iron Garnet is a marvel of nature. Its role in the physics of magnets is analogous to that of germanium in semiconductor physics, water in hydrodynamics, and quartz in crystal acoustics.”

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Yttrium Iron Garnet Y3Fe5O12 (YIG)

“Yttrium-Iron Garnet is a marvel of nature. Its role in the physics of magnets is analogous to that of germanium in semiconductor physics, water in hydrodynamics, and quartz in crystal acoustics.” YIG (the Father of Serpents) appears as a serpent man, serpent with bat-like wings, or as a giant snake. H.P. Lovecraft and Z. Bishop “The Curse of Yig” (1929)

• V. Cherepanov, I. Kolokolov, and V. L’vov, The saga of YIG:

spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet, Phys. Rep. 229, 81–144 (1993).

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Yttrium Iron Garnet Y3Fe5O12 (YIG)

“Yttrium-Iron Garnet is a marvel of nature. Its role in the physics of magnets is analogous to that of germanium in semiconductor physics, water in hydrodynamics, and quartz in crystal acoustics.”

48 oxygen atoms 8 octahedral iron atoms (spin 5/2 up) 12 tetrahedral iron atoms (spin 5/2 down) 12 dodecahedral yttrium atoms Unit cell

1 1 0 4 2 1 1 0 4 2 1 1 1 4 2 2 1 1 4 2

x y z

Magnetic moment

• f a unit cell is

10 Bohr magnetons at zero temperature Bulk YIG crystal

Wiki

• V. Cherepanov, I. Kolokolov, and V. L’vov, The saga of YIG:

spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet, Phys. Rep. 229, 81–144 (1993).

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Yttrium Iron Garnet Y3Fe5O12 (YIG)

“Yttrium-Iron Garnet is a marvel of nature. Its role in the physics of magnets is analogous to that of germanium in semiconductor physics, water in hydrodynamics, and quartz in crystal acoustics.”

48 oxygen atoms 8 octahedral iron atoms (spin 5/2 up) 12 tetrahedral iron atoms (spin 5/2 down) 12 dodecahedral yttrium atoms Unit cell Bulk YIG crystal Magnetic moment

• f a unit cell is

10 Bohr magnetons at zero temperature

1 1 0 4 2 1 1 0 4 2 1 1 1 4 2 2 1 1 4 2

x y z

Wiki

• V. Cherepanov, I. Kolokolov, and V. L’vov, The saga of YIG:

spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet, Phys. Rep. 229, 81–144 (1993).  Longest known magnon

lifetime (up to 700 ns )

 High Curie temperature

T ≈ 560 K

 Very low acoustic damping

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Yttrium Iron Garnet Y3Fe5O12 (YIG)

“Yttrium-Iron Garnet is a marvel of nature. Its role in the physics of magnets is analogous to that of germanium in semiconductor physics, water in hydrodynamics, and quartz in crystal acoustics.”

48 oxygen atoms 8 octahedral iron atoms (spin 5/2 up) 12 tetrahedral iron atoms (spin 5/2 down) 12 dodecahedral yttrium atoms Unit cell Single-crystal YIG film Magnetic moment

• f a unit cell is

10 Bohr magnetons at zero temperature

1 1 0 4 2 1 1 0 4 2 1 1 1 4 2 2 1 1 4 2

x y z

Scientific Research Company “Carat”, Lviv, Ukraine

• V. Cherepanov, I. Kolokolov, and V. L’vov, The saga of YIG:

spectra, thermodynamics, interaction and relaxation of magnons in a complex magnet, Phys. Rep. 229, 81–144 (1993).  Longest known magnon

lifetime (up to 700 ns )

 High Curie temperature

T ≈ 560 K

 Very low acoustic damping

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

dipolar interaction exchange interaction

Landau-Lifshitz equation:

Magnon spectrum

• f in-plane magnetized YIG film

2

q 

Thickness modes having a non-uniform harmonic distribution of dynamic magnetization along the film thickness

6 µm thick YIG film

2

q 

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon distribution

µ=0

Magnons are bosons (s=1) and similar to other quasi-particles are described in thermal equilibrium by Bose-Einstein distribution with zero chemical potential µ: chemical potential Bose-Einstein distribution

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Energy and momentum conservation laws

fp fp/2

Parametric pumping by electromagnetic wave at microwave frequency

Control of magnon gas density by parametric pumping

µ=0

µ: chemical potential Bose-Einstein distribution

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Energy and momentum conservation laws

fp fp/2

Parametric pumping by electromagnetic wave at microwave frequency

Control of magnon gas density by parametric pumping

Emin>µ>0

Bose-Einstein distribution µ: chemical potential Magnon thermalization due to 4-particle scattering: incoherent magnon gas

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Energy and momentum conservation laws

fp fp/2

Bose-Einstein magnon condensate

Bose-Einstein condensation of magnons

µ=Emin

Parametric pumping by electromagnetic wave at microwave frequency

µ: chemical potential Bose-Einstein distribution Magnon thermalization due to 4-particle scattering: incoherent magnon gas

S.O. Demokritov et al., Nature 443, 430 (2006)

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Brillouin light scattering spectroscopy

Frequency resolution Wavenumber uncertainty! Inelastic scattering of photons on magnons Stokes anti-Stokes Elastically scattered light

Magnon frequency

Intensity of the scattered light is proportional to magnon density

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Frequency resolution

Wavenumber resolution

Wavenumber resolution Max wavenumber 2.36×105 rad/cm Wavenumber resolution 0.02×105 rad/cm

 

magnon Laser

2 sin q q  

D.A. Bozhko, PhD thesis (2017)

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Time- , space- and wavevector-resolved BLS spectroscopy

(111) LPE YIG films 5 - 7 µm Width of the pumping area 50 and 500 µm Length of the pumping area 1 mm Max microwave power 100 W

Pinhole Objective Beam splitter

z y

Resolution

Time 1 ns Frequency 50 MHz Wavenumber 2×103 cm-1 Space 5 µm

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Time- , space- and wavevector-resolved pulsed BLS spectroscopy

(111) LPE YIG films 5 - 7 µm Width of the pumping area 50 and 500 µm Length of the pumping area 1 mm Max microwave power 100 W

Pinhole Objective Beam splitter

Resolution

Time 1 ns Frequency 50 MHz Wavenumber 2×103 cm-1 Space 5 µm AOM

z y

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon BEC: Experiment fp/2

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Magnon BEC: Experiment

pumping pulse pumping pulse BEC is formed during the pumping pulse is on BEC is formed after the pumping is off

Evaporative supercooling of strongly overheated low energy area of the magnon gas

Teff = 30 000 K

Serga et al., Nat. Commun. 5, 4452 (2014)

Small pump power Large pump power

Overpopulated low-energy magnon states Scattering

• f most energetic magnons

to upper spectral states

Bose-Einstein distribution

   

B

h exp 1 k D f f f T           

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

pumping pulse Pumping pulse end Freely evolving magnon BEC

Magnon BEC: Experiment

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Supercurrent in magnon BEC

Supercurrent : Flow of particles due to phase gradient

• f the condensate’s wavefunction

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Supercurrent in magnon BEC

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Supercurrent in magnon BEC

By changing probing laser power or laser pulse duration it is possible to control the phase of the magnon BEC

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser tLaser PLaser

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser tLaser PLaser

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser tLaser PLaser

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser tLaser PLaser

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser tLaser PLaser

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser

Magnon BEC

Dynamics of condensed magnons in thermal gradient

tLaser PLaser

Magnon gas

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Pump pulse 2 μs

tLaser

Probing laser pulse

PLaser

Parametric magnons Magnon BEC

Dynamics of condensed magnons in thermal gradient

Magnon gas

tLaser PLaser

No influence

• f a thermal

gradient

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - theory

Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b cr

( ) ( ) ( ) ( )

t

N N N e A N A N t N N A N A N A N N N N t N N A N N N N t



                         

cr

N  a critical number of magnons at which the chemical

potential

• f the magnon gas reaches



min



Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Supercurrent

Dynamics of condensed magnons in thermal gradient - theory

Additional decrease of population of condensed magnons due to magnon supercurrent

c( )

N t

( , ) J r t

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b cr

( ) ( ) ) ( ) ( , ( )

t

J N N N e A N A N t N N A N A N A N N N N t N N r A N N N N t r t



                            

 

c

, J r t N m  

2 2

( ) q m q    

2 c

| | N   arg( )   

BEC density: BEC phase: Magnon mass: Complex BEC wave function:

 

, r t 

Phase gradient

Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - theory

2 2

1 ( ) 2

y y

d q q D d  

2 2

1 ( ) 2

x x

d q q D d  

Anisotropic dispersion coefficients:

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b cr

( ) ( ) ( ) ( )

y t x

N N N e A N A N t N N A N A N A N N N N t N N A N N N N t J J x y



                                

Additional decrease of population of condensed magnons due to magnon supercurrent

c( )

N t

( , , ) J x y t

2D supercurrent

c x x

D J N x    

c y y

D J N y    

Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - theory

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b cr

( ) ( ) ( ) ( )

y t x

N N N e A N A N t N N A N A N A N N N N t N N A N N N N t J J x y



                                

2 2

1 ( ) 2

y y

d q q D d  

2 2

1 ( ) 2

x x

d q q D d  

Anisotropic dispersion coefficients

21

x y

D D

T x y

J J J 

Additional decrease of population of condensed magnons due to magnon supercurrent

c( )

N t

( , , ) J x y t

2D supercurrent

c x x

D J N x    

c y y

D J N y    

In experiment: Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - theory

T c x

D J N x    

c( )

x t   

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b cr T

( ) ( ) ( ) ( )

t

N N N e A N A N t N N A N A N A N N N N t N N A N N N N J t x



                            

Additional decrease of population of condensed magnons due to magnon supercurrent

c( )

N t

1D thermally driven supercurrent

T( , )

J x t

a weak frequency shift

• f the BEC wave function

due to temperature change Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t 21

x y

D D

T x y

J J J 

In experiment:

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - theory

g 3 3 g g g p gb g bg b 3 3 3 3 b b b gb g bg b bc b cr b cr 3 3 c c c bc b cr b c T dis r

( ) ( ) ( ) ( )

t

N N N e A N A N t N N A N A N A N N N N t J x N N A N N J N t x N



                               

Additional decrease of population of condensed magnons due to magnon supercurrent

c( )

N t

( )

x

J x x

c

N R R 

T

J

dis

J

T c x

D J N x    

c( )

x t   

1D thermally driven supercurrent 1D dispersive supercurrent

c dis x

D J x N    

Dynamics of condensed magnons , magnons in gaseous states and gaseous magnons at the bottom of SW spectrum described using balance equations

g( )

N t

c( )

N t

b( )

N t

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - comparison with theory

c( )

T t   

• D. A. Bozhko et al., Nat. Phys. 12, 1057 (2016)

 

c T

µm 300 µs

x

t x v D     

Supercurrent velocity

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - comparison with theory

c( )

T t   

Corresponding maximal temperature change 4.7 K

• D. A. Bozhko et al., Nat. Phys. 12, 1057 (2016)

Supercurrent velocity

 

c T

µm 300 µs

x

t x v D     

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - comparison with theory

c( )

T t   

COMSOL simulation using 3D heat-transfer model 5.7 K

• D. A. Bozhko et al., Nat. Phys. 12, 1057 (2016)

Supercurrent velocity

 

c T

µm 300 µs

x

t x v D     

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Dynamics of condensed magnons in thermal gradient - comparison with theory

c( )

T t   

COMSOL simulation using 3D heat-transfer model 5.7 K Supercurrent velocity

 

c T

µm 300 µs

x

t x v D     

Observed dynamics of magnon condensate can be understood taking into account magnon supercurrents

• D. A. Bozhko et al., Nat. Phys. 12, 1057 (2016)

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Control of supercurrent by density of pumped magnons

BLS intensity (counts)

Pump pulse

Time (ns)

Pump power (attenuation)

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

External experimental evidences

• f magnon supercurrents

Experiment Theory

Two coupled generalized Ginzburg-Landau equations

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Non-local measurements: supercurrent magnon transport

H

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Non-local measurements: supercurrent magnon transport

H

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Non-local measurements: supercurrent magnon transport

H

YIG Cu

40 K T  

Laser: 116 mW Temperature distribution simulated using COMSOL

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Non-local measurements: supercurrent magnon transport

S

m 350 s v 

S

m 350 s v  

40 K T  

Laser: 116 mW

H

Oleksandr Serha Seminar at the Center for Theoretical Physics of New York City College of Technology May 18, 2017

Summary



First evidence for magnon supercurrent in a room-temperature magnon Bose-Einstein condensate



Supercurrent depends on a phase gradient in the BEC wave function



The phase gradient can be induced both by temperature and density gradients



Magnon supercurrent can be controlled by the magnon gas density



Bose-Einstein magnon condensate with zero group velocity shows spatial spin transport