spin electricity conversion induced by spin pumping into ...yuki shiomi tohoku university &...
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Yuki ShiomiTohoku University & JST‐ERATO
Spin‐electricity conversion induced by spin pumping into topological insulators
NPSMP@ISSP
Phys.Rev.Lett. 113, 196601 (2014)
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arXiv:1312.7091 (2013)Phys.Rev.Lett. 113, 196601 (2014)
Spin injection into “bulk‐insulating” topological insulators
TI sampletheory boss
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TI is a promising material for spintronics application
=spin current ≠ 0electric current = 0
Topological Insulator (TI)
Surface: metalInterior: Insulator
spin‐momentum locking
(1)
(2)
surface property determined by bulk property(3)
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Spin injection into surface states of topological insulators
spin injection
Electric current = 0 ≠ 0
spin injection
Electric current induced by spin injection
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Spin‐electricity conversion induced by spin injection
spin injection
voltage
voltage
・Same symmetry as ISHE・Induced by spin‐momentum locking
(in principle, perfect conversion)
Inverse spin Hall effect
JsJc
spin injection
bulk
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Some trials for spintronics application of TI
Hall angle > 1
A.R.Mellnik, et al. Nature 511, 449‐451 (2014)
ST‐FMR
spin valve
C.H.Li, et al. Nature Nano. 9, 218‐224 (2014)
Y. Fan, et al. Nature Mat. 13, 699‐704 (2014)
Magnetization switching
Bulk insulating⇒ tiny electric current in TI
electric means
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Some trials for spintronics application of TI
Hall angle > 1
A.R.Mellnik, et al. Nature 511, 449‐451 (2014)
ST‐FMR
spin valve
C.H.Li, et al. Nature Nano. 9, 218‐224 (2014)
Y. Fan, et al. Nature Mat. 13, 699‐704 (2014)
Magnetization switching
Bulk insulating⇒ tiny electric current in TI
electric means
Bulk‐conductive TI ⇒ contaminated by bulk carriersBulk‐insulating TI ⇒ not‐efficient spin transfer (Res. mismatch)
How can we observe “pure” surface spin transport of TIs ?
・spin pumping : free from impedance mismatch (K.Ando 2011)・one more idea to minimize bulk‐carrier contribution
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Our experimental setup: Use of “Bulk form” topological insulators
Bulk‐carrier compensated TIs:Bi1.5Sb0.5Te1.7Se1.3 ,BiSbTeSe2 , Sn‐doped Bi2Te2Se
Bulk‐metallic TIs:Bi2Se3
0.1 mm No ISHE from bulk
sample thickness >> spin diffusion length
Insulator
Surface state
Voltage
T.Arakane, et al. Nat. Commun. 3, 636 (2011)A.A.Taskin, et al. PRL 107, 016801 (2011)
From Yoichi Ando(Osaka Univ.)
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Methods and samples
・ferromagnet :permalloy (Ni81Fe19) 20nm thick・coplanar‐type wave guide, network analyser (typically, 5 GHz is used)・measurement down to 15K (probe station)
HI
LO
Spin pumping
spin precession⇒ spin current
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Methods and samples
・ferromagnet :permalloy (Ni81Fe19) 20nm thick・coplanar‐type wave guide, network analyser (typically, 5 GHz is used)・measurement down to 15K (probe station)
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Spin pumping
Prof. Kentaro Nomura
= voltage generation
zzsdFsdF SJaepzvSJpzvH
・・・ ˆˆ
spin exchange interaction= torque
effsurface JMT
damping enhancement
aSpin pumping
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Voltage signals at FMR of Py at various temperaturesfor a Bi1.5Sb0.5Te1.7Se1.3 (BSTS) sample
High‐T : symmetric signal(Seebeck effect)
Asymmetric signal
Sign inversion between +H and ‐H
FMR
Correlation to surface conductionbeing dominant at low Ts
heating
depend on environment
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Correlation between antisymmetric voltage signals and surface transport
Va increases with decreasing T
・NOT shunting of AMR
・NOT Nernst effect
RBSTS ≈ Rpy (≈ 5Ω) at 300 KRBSTS >> Rpy at low Ts
×2
∝ T at low Ts(Mott relation)
×10 !!
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NO antisymmetric signal in control samples: bulk‐metallic TIs (Bi2Se3); conventional semiconductors
・Reproducible for all BSTS samples・not observed for BS1, n‐Si, or n‐InAs
Anti‐symmetric signals ariseon topological surface states 0 100 200 30010-4
10-3
10-2
10-1
100
101
(
cm)
T (K)
BSTS1
BSTS2
BS1, BS2
BSTS3
n-Si
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Mechanism of spin‐electricity conversion effect
“spin‐momentum locking” ⇒ spin‐electricity conversion
Prof. Kentaro Nomura
same sign as the experiment
spin injectionshift of the Fermi circle
n‐type
if Hall angle θ defined, θ~1%ISHE
JsJc
spin injection
bulk
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Summary & perspective
・observation of anti‐symmetric signals on millimeter‐thick bulk‐insulatingTIs
・anti‐symmetric signals arise on surface states・build a model:new spin‐electricity conversion
the voltage sign is consistent in principle, high efficiency up to 100%, but only ~ 1% now.
Phys.Rev.Lett. 113, 196601 (2014)
・improve the efficiency (improve interface quality, reduce magnetic proximity effect, etc.)
・experiments in BSTS|YIG systems
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Bi1.5Sb0.5Te1.7Se1.3 plate(50 nm thick)
Growth of BSTS plates on Mica substrate ⇒ transfer onto YIG
Catalyst‐free vapor solid method
BSTS plate (~ 1mm size) ⇒ transfer onto YIG
D.Kong, et al. Nano Lett. 10, 2245‐2250 (2010)
H.Li, et al. JACS. 134, 6132‐6135 (2012)
Mica
Au(20nm)|YIGBy Dr. Tanabe (Tohoku Univ.)
Perspective: BSTS on YIG