magnonic wiedemann-franz law
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Kouki Nakata
University of Basel
All the responsibilities of this slide rest with Kouki Nakata (Dec. 2016) Enjoy also talk by DL : https://www.youtube.com/watch?v=56T4CmjkA5c&list=PLS3nw8GL8hAXeJFCXcziJMHB1Yb_HLncd
Magnonic Wiedemann-Franz Law
KN, P. Simon, and D. Loss: Phys. Rev. B 92, 134425 (2015) See also [KN, J. Klinovaja & D. Loss (2016), arXiv:1611.09752] & review article [KN, P. Simon & D. Loss, arXiv:1610.08901]
Magnon Carries ๐B & ๐B
โค โช
Magnon ๐B ๐B
Low-energy collective mode in insulating magnet
Yes !
QUESTION
Can magnon ๐B (boson) transport be similar to electron ๐ (fermion) transport ?
Electron ๐ = Fermion
Magnon ๐B = Boson
Wiedemann-Franz (WF) law Franz and Wiedemann, Annalen der Physik (1853)
Magnonic Wiedemann-Franz law KN, P. Simon & D. Loss, PRB (2015)
Superconductors
Onnes (1911)
Quasi-equilibrium magnon condensate Demokritov et al., Nature (2006)
Condensed magnon current Hillebrands-group, Nat. Phys. (2016)
Josephson effect Josephson, Phys. Lett. (1962)
Magnonic Josephson effect KN, K. A. van Hoogdalem, P. Simon & D. Loss, PRB (2014)
KN, P. Simon & D. Loss, PRB (2015)
Quantum Hall effetc (QHE) Klitzing et al., PRL (1980)
Magnonic QHE KN, J. Klinovaja & D. Loss (2016), arXiv:1611.09752
QUESTION
Can magnon ๐B (boson) transport be similar to electron ๐ (fermion) transport ?
See review article [KN, P. Simon & D. Loss, arXiv:1610.08901]
Universal Thermomagnetic Relation of Magnon Transport
๏ผ
GOAL
for electron transport in metals
Wiedemann-Franz Law
Y. Kajiwara et al., Nature 464, 262 (2010)
Wiedemann-Franz Law in Metals Franz and Wiedemann, Annalen der Physik 165, 497 (1853)
Universal Lorenz number:
At low temperature ๐ โช ๐F/๐B~104 K
๐พ: Thermal conductivity ๐: Electrical conductivity
Thermoelectrics in Metal
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
โ
Charge
Heat
โ
Charge
Heat
K
Thermal Conductivity ๐พ โ ๐ฟ22 for Fermions
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
?
*Lifshitz & Pitaevskii (Vol. 10)
*
โ
Magnon
Thermal Conductivity ๐พ โ ๐ฟ22 for Magnons KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
K
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
Heat
Thermal Conductivity ๐พ โ ๐ฟ22 for Magnons
Textbook by Ashcroft & Mermin Eq. (13.56): K is measured under conditions of no quasi-particle current
๐m = ๐ฟ11๐ต๐ต โ๐ฟ12๐ต๐ = 0 ๐ต๐ตโ =๐ฟ12
๐ฟ11๐ต๐
!
๐๐ = ๐ฟ21๐ต๐ตโโ ๐ฟ22๐ต๐ = โ(๐ฟ22โ ๐ฟ21๐ฟ12/๐ฟ11)๐ต๐
Thermal conductivity ๐พ: ๐๐ โก โ๐พ โ ๐ต๐ with !
๐m = 0
K
Magnetization gradient
Johnson & Silsbee (1987) Basso et al. (2016)
โ
Magnon K
Heat
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Thermomagnetics in Ferromagnetic Insulator (FI)
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
โ
Magnon
Heat
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
โ
Magnon
Heat
Thermomagnetics in Ferromagnetic Insulator (FI)
Magnon Seebeck ๐ฎ
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
โ
Magnon
Heat
Magnon Peltier: ฮ
Thermomagnetics in Ferromagnetic Insulator (FI)
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
โ
Magnon
Heat
Onsager relation
Thermomagnetics in Ferromagnetic Insulator (FI)
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
โ
Magnon
Heat
Thermomagnetics in Ferromagnetic Insulator (FI)
Seebeck & Peltier
WF law ๏ผLow temp.๏ผ
?
?
Electron = Fermion Magnon = Boson Textbook by Ashcroft & Mermin
Lorenz number =
= =
=
WF
? ?
*
*Lifshitz & Pitaevskii (Vol. 10)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
QUESTION
Magnonic Wiedemann-Franz Law
Magnon ๐B : Boson
Electron ๐ : Fermion
Bose-Einstein statistics vs Fermi-Dirac statistics
Specific heat of electrons๏ผ
๐el โ ๐ Specific heat of phonons๏ผ
๐ph โ ๐3
WELL-KNOWN: Qualitatively different behavior at low temperature
Q. Still, Linear-in-๐ behavior for bosons ? Universal ?
Magnon current:
Heat current:
Onsager matrix ๐ฟ๐๐ :
System: Ferromagnetic Insulating Junction
Driving forces: โช ๐ต โช ๐
๐๐L(R) = 2๐ฝ๐๐2๐2+๐๐๐ต๐ตL(R)
Tunneling:
Weak coupling :
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Magnon & Heat Currents
Magnon current
Heat current
๐: Magnon lifetime: Phenomenologically introduced
Linear response
Bose function
Onsager relation:
Onsager Matrix ๐ฟ๐๐
Polylogarithm function:
Exponential integral:
Euler constant: Cross-section area of the junction interface:
๐ฟ๐๐ depends on material
Onsager relation
Magnon current
Heat current
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Onsager Matrix ๐ฟ๐๐
Polylogarithm function:
Exponential integral:
Euler constant: Cross-section area of the junction interface:
๐ฟ๐๐ depends on material
Onsager relation
Magnon current
Heat current
NOTE: ๐ ๐ โก๐๐B๐ต
๐B๐โ at low temperature
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
๐๐B๐ต
๐B๐
Magnetic conductance ๐บ:
: For fermions
Thermal conductance ๐พ for magnons (bosons)
Magnon WF law
Wiedemann-Franz Law for Magnons
Magnon current
Heat current
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Wiedemann-Franz Law for Magnons
Low temp.๏ผ
Magnon Lorenz number: UNIVERSAL
Independent of materials
e.g., ๐ = 100ns, ๐ โค 1K & ๐ต = 5T
(If omitted the off-diagonal ๐ฟ21 & ๐ฟ12 The WF law is not reproduced)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Note: 1) We checked that 3- and 4-magnon processes are negligible at low temp.
KN et al., PRB 92, 134425 (2015)
2) At ๐ = ๐ช(10โ1) K, phonon contributions are negligible
Adachi et al., APL 97, 252506 (2010)
3) The WF law holds in dipole-dipole int. (YIG)
Wiedemann-Franz Law for Magnons
e.g., ๐ = 100ns, ๐ โค 1K & ๐ต = 5T
(If omitted the off-diagonal ๐ฟ21 & ๐ฟ12 The WF law is not reproduced)
Low temp.๏ผ
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
VS
(Free electron at low temp.) Low temp.๏ผ
Electron (metal) Magnon (FI)
R. Franz and G. Wiedemann, Annalen der Physik 165, 497 (1853)
KN, Simon, and Loss, Phys. Rev. B 92, 134425 (2015)
Fermion Boson Statistics
Lorenz number
WF law ๏ผLow temp.๏ผ
SUMMARY
Onsager-Thomson relation
Seebeck & Peltier
Ratios of ๐ฟ๐๐ , WF law, Seebeck, and Peltier coefficients are material independent
Magnonic Wiedemann-Franz Law: KN, P. Simon, and D. Loss, Phys. Rev. B 92, 134425 (2015) See also [KN, J. Klinovaja & D. Loss (2016), arXiv:1611.09752] & review article [KN, P. Simon & D. Loss, arXiv:1610.08901]
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