Conversion)from)a)charge)current)into)a)spin)polarized ... · Conversion)from)a)charge)current)into)a)spin)polarized)current) in)thesurface)state)ofthree 6dimensional)topological)insulator

Conversion from a charge current into a spin polarized current in the surface state of three-dimensional topological insulator

New Perspectives in Spintronic and Mesoscopic Physics

Symposium @Kashiwa2015.06.12

Yuichiro Ando1, Satoshi Sasaki2, Kouji Segawa2, Yoichi Ando2, and Masashi Shiraishi1

1. Department of Electronic Science and Engineering, Kyoto University2. Institute of Scientific and Industrial Research, Osaka University

Y. Ando et al., Nano Lett. 14, 6226(2014).

Acknowledgments

Kyoto Univ.Detection of spin current

Osaka Univ.Fabrication of TI

Prof. Yoichi Ando Prof. Kouji Segawa

Dr. Satoshi Sasaki

Dr. Fan Yang

Dr. Mario Novak

Mr. TakahiroHamasaki

Prof. Masashi Shiraishi

Mr. TakayukiKurokawa

The surface state in 3D topological insulator

Surface state of topological insulator 2D metallic surface stateDirac electron system

1/25

Topological Insulator Topologically-trivialInsulator, semiconductor

Valanceband

Conductionband

Valance band

Fermi Level, EF

E

k-k 0

E

k-k 0

Spin-momentum locking in 3D topological insulator 2/25

Spin-momentum locking

I < 0

Jc

I > 0

JcJc Jc

I < 0

Jc

I > 0

JcJc Jc

Surface state of topological insulator (TI) 2D metallic surface stateDirac electron system

Electrical injection/extraction of the spin polarized current due to charge flow in the surface state of the topological insulator

Objective

Verification of surface state of 3D topological insulator

T. Arakane et al., Nat. Comm. 3, 636 (2012).

Band structure of surface (Angle-Resolved Photo Emission Spectroscopy)

TlBiSe2

T. Sato et al., Phys. Rev. Lett. 105, 136802 (2010).

Bi2Sb2-XTe3Se3-Y

3/25

Verification of surface state of 3D topological insulator

Two dimensional transport properties

A. A. Taskin et al., Phys. Rev. Lett. 109, 066803 (2012).

Shubnikov-de Haas oscillations Weak-antilocalization

Z. Ren et al., Phys. Rev. B 82, 241306(R) (2010).

Bi2Se3 thin film

Bi2Te2Se Bi2Se3 thin film

4/25

Detection of spin accumulation in topological insulator

This studyBulk-insulating TI Extraction of spin currentby electric fields.(Local magnetoresistance)

5/25

Thickness of Bi2Se3:10 nm

Ferromagnetic metal (FM)

Nonmagnetic metal (NM)

Magnetoresistance using nonlocal three-terminal scheme

B

TI

I

Vmeas

Magnetization of FM(spin angular momentum of majority spin: )

Magnetic field, B

e-

e-Interface resistance at FM

TI

TI

TI

Vmeas

TI TI

e-

0

6/25

Magnetic field, B

Magnetoresistance using nonlocal three-terminal scheme

Interface resistance at FM

B

TI

I

Vmeas

Change of current-voltage configuration Change of current direction

B

TI

Vmeas B

TI

I

VmeasI

Charge current direction

Charge current direction

Magnetic field, B

e-

Interface resistance at FM

e-

e-

e-

0

7/25

Device fabrication procedure

TI SiO2/Si sub.

Sample : Single crystal Bi1.5Sb0.5Te1.7Se1.3 (BSTS) & Bi2Se3 formed by a Bridgeman method

Substrate : Thermally-oxidized SiO2 (500 nm) / SiTI flakes : Mechanical exfoliation using a Scotch tape Thickness of TI-flake : Laser microscope& Atomic force microscope.Ni80Fe20(Py) & Au/Cr electrode : Electron beam lithography

& Electron beam evaporation.

Unit layer(5 Layers)

van der Waals' force

8/25


Sample : Single crystal Bi1.5Sb0.5Te1.7Se1.3 (BSTS) & Bi2Se3 formed by a Bridgeman method

Substrate : Thermally-oxidized SiO2 (500 nm) / SiTI flakes : Mechanical exfoliation using a Scotch tape Thickness of TI-flake : Laser microscope& Atomic force microscope.Ni80Fe20(Py) & Au/Cr electrode : Electron beam lithography

& Electron beam evaporation.


Unit layer(5 Layers)

van der Waals' force

1 m

TI

SiO2

B

I Vmeas2 1 3

Au/CrFerromagneticmetalNi80Fe20(Py)

8/25Device fabrication procedure

0.0

1.0 10-2

2.0 10-2

3.0 10-2

0 100 200 300

BST

S(cm)

Temperature (K)

BSTSt = 45 nm

BSTSt = 58 nm

Temperature dependence of resistivity

IIIV

1 2 3 4

+-- +

TI

r

Temp.

BSTS

r

Temp.

Bulk : SemiconductorBand gap : 0.3eV

Surface : Metallic

9/25

0.0

1.0 10-2

2.0 10-2

3.0 10-2

0 100 200 300

BST

S(cm)

Temperature (K)

BSTSt = 45 nm

BSTSt = 58 nm

IIIV

1 2 3 4

+-- +

TIBulk conduction band

Bulk valance band

EF

BSTS

9/25Temperature dependence of resistivity

0.0

1.0 10-2

2.0 10-2

3.0 10-2

0.0

4.0 10-4

8.0 10-4

1.2 10-3

0 100 200 300

BST

S(

cm

) BS (

cm

)

Temperature (K)

BSTSBi2Se3

t = 65 nmt = 45 nm

BSTSt = 58 nm

IIIV

1 2 3 4

+-- +

TIBulk conduction band

Bulk valance band

EF

BSTS

Bi2Se3

Bulk conduction band

Bulk valance band

EF

9/25Temperature dependence of resistivity

466.24

466.28

466.32

466.36

466.4

-1000 0 1000Magnetic Field (Oe)

R int

.2 (

)

0.04W

I =100 mA

Device A

Magnetoresistance in BSTS devices at 4.2 K

B

TI

I

Vmeas

e-

e-

Magnetization of FM(Spin angular momentum of majority spin: ) e-

4.2 K

10/25

466.24

466.28

466.32

466.36

466.4


R int

.2 (

)

0.04W

I =100 mA

Device A

B

TI

I

Vmeas

Anisotropic magnetoresistanceAMR)

Contact 2 : Py Au/PySuppression of the Dip signals

e-

e-

Magnetization of FM(Spin angular momentum of majority spin: ) e-

4.2 K

10/25Magnetoresistance in BSTS devices at 4.2 K

451.94

451.98

452.02

452.06

452.10


R int

.2 (

)

466.24

466.28

466.32

466.36

466.4


R int

.2 (

)

0.04W0.04W

4.2 K

I =100 mA I =-100 mA

Device A Device A

B

TI

I

Vmeas

e-

e-

e-

e-

10/25Magnetoresistance in BSTS devices at 4.2 K

Reversal of the current-voltage scheme

173.1

173.2

173.3

173.4

173.5

173.6

-400 -200 0 200 400Magnetic Field (Oe)

R int

.2 (

)

177.2

177.3

177.4

177.5

177.6

177.7


R int

.2 (

)

I =-100 mA

B I

Vmeas B Vmeas I

0.1W 0.1W

I =-100 mA

Device BDevice B

4.2 K

11/25

79.46

79.48

79.5

79.52

79.54

-400 0 400

R 2 (

)

Magnetic Field (Oe)

Device D

82.58

82.6

82.62

82.64

82.66

-1000 -500 0 500 1000

R 2 (

)

Magnetic Field (Oe)

0.02 W

4.2 KI = -100 mA

Magnetoresistance at B // I

B I

Vmeas B I

Vmeas

Device D

4.2 KI = -100 mA

4.2 K

12/25

102.5

102.54

102.58

102.62

102.66


R 2 (

)

102.16

102.2

102.24

102.28

102.32

-1000 -500 0 500 1000

R 2 (

)

Magnetic Field (Oe)

Magnetoresistance in Bi2Se3 devices

I =100 mA I =-100 mA

0.04W 0.04W

No rectangular hysteresis signals

4.2 K

13/25

Estimation of charge current density in the surface state 14/25

30 nm

300 nm10 nm

500 nm

2000 nmTI

Au/CrPy

3 nm

TI surface

TI bulk

sPy=2.50100 W-1mm-1sBS surface=2.13100 W-1mm-1sBSTS surface=2.3210-2 W-1mm-1sBS bulk=2.7210-1 W-1mm-1sBSTS bulk=2.1010-5 W-1mm-1

Z. Ren et al., Phys. Rev. B 84, 165311(2011).H. Steinberg et al., Nano Lett. 10, 5032(2010).

Bi2Se3I

BSTSI

30 nm

x

z

300 nm10 nm

500 nm

2000 nmTI

Au/CrPy

3 nm

TI surface

TI bulk

Estimation of charge current density in the surface state


x

z


14/25

Bi2Se3I

BSTSI x

z

Estimation of charge current density in the surface state

Spin polarization: High

Spin polarization: Low

x

z

14/25

30 nm

300 nm10 nm

500 nm

2000 nmTI

Au/CrPy

3 nm

TI surface

TI bulk



470.78

470.82

470.86

470.90

470.94


R int

.2 (

)

0.04W

300 K

489.62

489.66

489.70

489.74

489.78


R int

.2 (

)

0.04W

I =100 mA I =-100 mA

Rectangular hysteresis signals : DisappearedAMR signals : Observed

Magnetoresistance in BSTS devices at 300 K

Device A

15/25

Disappearance of the rectangular signals : 150~200 K

0

0.005

0.01

0.015

0.02

0.025

0.03

0 50 100 150 200 250 300R i

nt_2

()

Temp. (K)

Device B I =-100 mA

16/25Magnetoresistance in BSTS devices at 300 K


0

0.005

0.01

0.015

0.02

0.025

0.03

0 50 100 150 200 250 300R i

nt_2

()

Temp. (K)

Device B I =-100 mA

0.0

1.0 10-2

2.0 10-2

3.0 10-2

0 100 200 300

BST

S(cm)

Temperature (K)

BSTSt = 45 nm

BSTSt = 58 nm

"#$# @4.2"#$# @300

= 1.07~1.43

Considerable surface conduction at 300 K.

"#$# @8"#$# @300

= 10~100

Y. Ando JPSJ 82, 102001 (2013).

Several mm thick BSTS

16/25

0

0.005

0.01

0.015

0.02

0.025

0.03

250

300

350

400

0 50 100 150 200 250 300R i

nt_2

() R

channel ()

Temp. (K)


Device B I =-100 mA

0.0

1.0 10-2

2.0 10-2

3.0 10-2

0 100 200 300

BST

S(cm)

Temperature (K)

BSTSt = 45 nm

BSTSt = 58 nm

"#$# @4.2"#$# @300

= 1.07~1.43

Considerable surface conduction at 300 K.

16/25

Spin-charge coupled transport equations

Spin drift-diffusion equations with spin-momentum locking

=

7 + 2

>

=27>

7 +327>

7 + 7A

>

+ >

A

=27A

7 +327A

7 + 7>

A

+ A

17/25

Assuming dSx/dy=0,dSy/dy=0

Boundary conditions

Spin density along x direction


77 + 2

A

= 0327A

7 A

+ = 0

|>GI/7 =

32A

|>GMI/7 =

A

|>GI/7 = 0

A =P

23 2 / 3/2 2/ 3/2

2P

18/25

72

=47P

Charge current

Spin dependent voltagedue to spin momentum locking


=1

P`

=27P

+47P

I/7

MI/7

7= 7

451.94

451.98

452.02

452.06

452.10


R int

.2 (

)

0.04W

4.2 K Device A

7

19/25

72

=47P

Charge current

Bias current dependence of the spin signal

7= 7 4.2 K

Device B

-2 10-5

-1 10-5

0

1 10-5

2 10-5

-100 0 100I ( A)

V 2 (V

)

19/25

Spin dependent voltagedue to spin momentum locking

=1

P`

=27P

+47P

I/7

MI/7

10010-6 [A=C/s] 1.0510-34 [Js=CVs]

Spin polarization of injected current

1.6010-19 [C] 0.05~0.1 -1 from ARPES(S. Kim et al., Phys. Rev. Lett. 112, 136802 (2014).)

Width of TI channel2000 [nm] =2104 []

This study: 2V=440mV=0.05~0.5%

Magnetoresistance

Estimation of spin injection and extraction efficiencies

=1

P`

=27P

+47P

I/7

MI/7

20/25

72

=47P

Charge current through the bottom surface

I

BSTS

21/31


-0.08-0.06-0.04-0.02

00.020.040.060.08

-4 10-5 -2 10-5 0 2 10-5 4 10-5

2-35-6

Vol

tage

(V)

Current(A)

4.2 K

II +-

BSTS

I IVV1 2 3 4 5 6

Path 1Path 2


Path 1

Path 2

21/31

I

BSTS


= bd(1 ( + P) + P))

1 7

+jMk + MMk P +

4d(P )1 7

Mk + Mk P P +

4d( )1 7

4 n

(in TI) = jMkrs + + d,

= MMkrs + + d ,

(in Py) u =

MkMrsw + + ,

u =

MkMrsw + + ,

One dimensional spin drift-diffusion model

Effect of the interface resistance on the spin injection efficiency

m

z

z

m

Py BSTS 22/25

10-6

10-5

10-4

10-3

10-2

10-1

100

10-16 10-14 10-12 10-10

R 2 (

)

Resistance area ( m2)


sPy= 2.50 W-1mm-1ssur_iTI = 2.3210-2 W-1mm-1PF = 0.5 %

23/25Saturation region

10-6

10-5

10-4

10-3

10-2

10-1

100

10-16 10-14 10-12 10-10

R 2 (

)

Resistance area ( m2)


sPy= 2.50 W-1mm-1ssur_iTI = 2.3210-2 W-1mm-1PF = 0.5 %

Saturation region 23/25

The conductance mismatch problem is not crucial issue.

Possible origin of the low spin injection efficiency

Unoptimized spin injection and extraction geometry

Low quality Py/TI interface (e.g. Intermixing TI and FM)

Carrier momentum change Spin angular momentum change??

TI

Insertion of MgO or Al2O3 tunnel barrier Improvement of device fabrication procedure

e.g., Ferromagnetic materials,Low temperature deposition

Py

24/25

TI Py

177.2

177.4

177.6


R int

.2 (

)Summary

We have demonstrated the electrical injection and extraction of the spinpolarized current due to spin-momentum locking of bulk-insulatingtopological insulator Bi1.5Sb0.5Te1.7Se1.3

102.5

102.54

102.58

102.62

102.66


R 2 (

)

4.2 K4.2 K

Y. Ando et al., Nano Lett. 14, 6226(2014).

Bi1.5Sb0.5Te1.7Se1.3 Bi2Se3

25/25

Local magnetoresistance Spin injection/extraction efficiency: 0.05~0.5%

(BSTS>>Bi2Se3) Detectable temperature: 4.2~200 K

=y=

y7

47P= 16.7%

Spin Polarization in TI

y = 100

=110M| 210M}[]

= 50[AMk]

y =1.610Mk 0.17[]4 6.5810Mk} 7 []

= 300[AMk]

-4

0

4

-400 -200 0 200 400

Vol

tage

(V

)

Magnetic field(Oe)

-4

0

4

-400 -200 0 200 400

Vol

tage

(V

)

Magnetic field(Oe)

4.2 K

I =1 mA I =-1 mA

4.2 K

1 2 3 4

VI

-+

+-

Spin accumulation measurements

-0.08-0.06-0.04-0.02

00.020.040.060.08

-4 10-5 -2 10-5 0 2 10-5 4 10-5

2-35-6

Vol

tage

(V)

Current(A)

4.2 K

II +-

BSTS

I IVV1 2 3 4 5 6

Disconnected

TI PyI-V

Path 1Path 2

1 m

Au/Cr

TI

Py

SiO2

H

I Vmeas2 1 3

xz

y

No electric conduction

Charge current through the bottom and side surface

Path 1

Path 2

4.2 K

Bias current dependence of DV2

A linear relationship between DV2 vs I

4.2 KDevice B Device D

-2 10-5

-1 10-5

0

1 10-5

2 10-5

-100 0 100I ( A)

V 2 (V

)

-4 10-6

0

4 10-6

-200 -100 0 100 200I ( A)

V 2 (V

)

102.5

102.54

102.58

102.62

102.66


R 2 (

)

102.16

102.2

102.24

102.28

102.32


R 2 (

)

116.5

116.54

116.58

116.62

116.66


R 2 (

)

116.06

116.1

116.14

116.18

116.22


R 2 (

)

R2-H curves of Bi2Se3 devices

4.2 K4.2 K

I =100 mA I =-100 mA

0.04W

0.04W 0.04W

0.04W

300 K300 K

No rectangular hysteresis signals

Charge circuit Voltage measurement

N M N MF M N M

T I

Charge circuit Voltage measurement

N M N MF M

T I

Charge circuitVoltage measurement

N M F M

T I

(b) Nonlocal magnetoresistance

(c) Three terminal local (This study)

(a) Local magnetoresistance

Magnetoresistance

Spin voltage

Magnetoresistance

(a)

0

0.005

0.01

0.015

0.02

0.025

-400 -200 0 200 400EG (MV/m)

R int

. ()

77.64

77.66

77.68

77.7

-400 -200 0 200 400Magnetic field (Oe)

R int

. ()

I = 100 ATemp. = 100 KEG= 0 MV/m

(b)

840.5

841.0

841.5

842.0

842.5

-400 0 400

R int

.2 (

)

Magnetic field (Oe)

I =50 mA

0.5 W

4.2 K

0

0.2

0.4

0.6

0 100 200 300

R int

.2 (

)

Temperature (K)

I =50 mA

Temperature dependence of DR2 (Device B)

Rectangular hysteresis signals disappeared at 150 K

High charge current density ( > 100 ~ 1000 mA)Large interface and channel resistances

A technical issue

The TI devices were easily broken.

Au/Cr Py Au/Cr Py

Spurious effects expected in FM/TI devices

Anisotropic Magnetoresistance (AMR) Planar Hall effect (PHE) Anomalous Hall effects (AHE) Lorenz MR Tunneling Anisotropic Magnetoresistance (TAMR)

Magnetization & charge current

Anomalous Nernst effects (ANE) Spin Seebeck effect (SSE)

.etc

Magnetization & Thermal gradient

A strong TI dependence and temperature dependence of therectangular signals cannot be explained as a result of thespurious effects.


Anisotropic Magnetoresistance(AMR)

IMrM//I rMI

Planar Hall effect (PHE)V0

Anomalous Hall effect (AHE)V0

Difference betweenBS and BSTS devices?????


Lorenz MR

Tunneling Anisotropic Magnetoresistance (TAMR)

Stray field

Disappearance of the rectangular signals at 300 K &Clear AMR signals at 300K ???

Discrepancy between AMR signals and Rectangular signals ??

Origin: An anisotropic density of states[C. Gould et al., PRL 93, 117203(2004).]

Interference of Rashba and Dresselhausspin-orbit interactions[L. Moser et al., PRL 99, 056601(2007).]

Low spin injection efficiency (=0.0005~0.005)

E. Villamor Phys. Rev. B 88, 184411 (2013).

Spin polarization of Py

Py/metal interface 0.2~0.4

Small temperature dependence


= bd(1 ( + P) + P))

1 7

+jMk + MMk P +

4d(P )1 7

Mk + Mk P P +

4d( )1 7

4 Mk + Mk + Mk + Mk P +

4d1 7

n

(in TI) = jMkrs + + d,

= MMkrs + + d ,

(in Py) u =

MkMrsw + + ,

u =

MkMrsw + + ,

One dimensional spin drift-diffusion model


Nonlocal magnetoresistance

I

I

Local magnetoresistance

FM

NM FM NM

NM NM

Bulk-metallic TI

Bulk-metallic TI

I

FMNM NM

I

NM FM NM

Bulk-insulating TI

Bulk-insulating TI

610-3 [A/mm-2]

30 nm

x

z300 nm

10 nm500 nm

2000 nmTI

Nonmagnetic metal (NM)Ferromagnetic metal (FM)

4

2

0

-2

3 nm

TI surface

TI bulk

BS Local Current : z-directionI

BSTS Local Current : z-directionI

BS Non local Current : z-directionI

BSTS Non local Current : z-directionI

BSTS Local Current : x-direction real scale

Documents

Conversion)from)a)charge)current)into)a)spin)polarized ... · Conversion)from)a)charge)current)into)a)spin)polarized)current) in)thesurface)state)ofthree 6dimensional)topological)insulator