Graduate School of Science, Osaka University

Tomonori Arakawa

JapanJ. Shiogai (Institute for Materials Research, Tohoku University)

K. Kobayashi, M. Maeda (Osaka University)T. Ono (Kyoto University)

M. Kohda, J. Nitta (Tohoku University)Germany

M. Ciorga, M. Utz, D. Schuh, D. Bougeard , D. Weiss (University of Regensburg )

This work was partially supported by the JSPS Funding Program for Next Generation World Leading Researchers (GR058) and Grant-in-Aid for Scientific Research on Innovative Areas (25103003).

Collaborators;

Acknowledgment;

Collaboration started since 2011

1

Introduction◦ What is Shot noise and how to measure it◦ Shot in mesoscopic system◦ Potential of Shot noise in spintronics

Our result◦ Remind for spin current◦ Experimental results

Conclusion and future plan

2

I

Time

sample

R = 1/GV

I

FFT

Current noise spectral density

Y. M. Blanter and M. Büttiker, Phys. Rep. 336, 1 (2000).

3

Thermal noiseJohnson-Nyquist (1928)

A

E

EFsystemV=0

Thermal fluctuation

𝑆𝑆thermal = 4𝑘𝑘𝐵𝐵𝑇𝑇𝑒𝑒𝐺𝐺

A

Shot noiseSchottky (1918)

system

E

EFV≠0

𝑆𝑆shot = 2𝑒𝑒∗ 𝐼𝐼 𝐹𝐹Electron Temperature

Partition process

Fano factor

Powerful tool to investigate transport processesReview: Y. M. Blanter and M. Büttiker, Phys. Rep. 336, 1 (2000).

Effective charge

4

X. Jehl et al., Nature 405, 50 (2000).

N S

Cooper pair transport

e*/e=2

L. Saminadayar et al., PRL 79, (1997).

Fractional quantum Hall effect

e*/e=1/3

D. C. TsuiH. L. StörmerR. B. Laughlin

1998 Nobel Prize

M. Hashisaka et al., PRL 114, (2015).

R. de-Picciotto et al., Nature 389, (1997).

A. Kumar et al., PRL 76 2778 (1996).

Statistical properties of quantum channels

( )1n nnnn

T TF

T−

= ∑∑

0

SPINTRONICS

MESOSCOPICS

TeruoOno

Kensuke Kobayashi

Spin transport

Target

Shot noise measurement

Probe

MotivationSpin dependent transport probed by Shot noise measurement

6

T. Arakawa et al., Appl. Phys. Lett. 98, (2011).

T. Tanaka, T. Arakawa et al., APEX 5, (2012).

insulator

FM electrode FM electrode

Kai Liu et al., PRB 86, (2012).

M. Kohda et al., Nat. Commun. 3, (2012).

Spin filter effect

QPC

Direct proof for Coherent tunneling theory

Tunnel Magnetresistance effect

Estimation of Spin polarizationTheory

Experiment Experiment

7

E. G. Mishchenko, PRR B 68, (2003).W. Belzig and M. Zareyan, PRB 69, (2004).

Spin flip process in diffusive conductor

A. Lamacraft, PRB 69, 081301 (2004).

B. Wang et al., PRB 69, (2004).

S. I. Erlingsson and D. Loss, PRB 72, (2005).

A. Chudnovskiy et al., PRL 101 (2008).

R. L. Dragomirova et al., EPL 84, (2008).

J. Meair et al., PRB 84, (2011).

O. Sauret and D. Feinberg, PRL 92, (2004).

A lot of theoretical predictions

Shot noise of spin current

Spin torque phenomenon

Spin Hall effect

Spin accumulation

A few experimental reports

etc….8

T. Arakawa et al., PRL 114, 016601 (2015).9

sample

sample

CI I I↑ ↓= +Charge current

eV

Bias voltage

sample

SI I I↑ ↓= −Spin current

µ∆

Spin accumulation

Spin flip processindependent

10

E

Tunnel barrier

eVIS

V

( )2IS e I I↑ ↓= +E

µ∆ IS

µ∆

I

V

total

I

total

µ∆11

IS

V

total

µ∆

Eµ∆

+

eV

Direct measurement of Spin current and Δμ without ferromagnet

or Invers spin Hall effect

I I↑ ↓= − C 0I = S0I ≠

Pure spin current

S2S e I F=

12

50 nm (Ga0.945Mn0.055)As

2.2 nm (Al0.35Ga0.65)As

8.0 nm n+-GaAs (n+=5-6×1018cm-3)15 nm n+→n-GaAs

1μm n-GaAs (n=2-4×1016cm-3)

500 nm [AlGaAs/GaAs ]50300 nm GaAs

GaAs substrate

50 μm

5 μm

lateral all-semiconductor spin valve device

P-type (FM)

n-type (Normal)Tunnel barrier

M. Ciorga et al., PRB 79, 165321 (2009). J. Shiogai et al., APL 101, 212402 (2012).

13

Spin accumulation

F. J. Jedema et al., Nature 410, 345 (2001).

V P µ∆ = ∆

1 2

1 2

0.82T TPT T−

= =+

14

Modulate V and Δμ independently

Measure SI and I

PE

µ∆

+

eV

AP

n-GaAs GaMnAs15

IS

V

total

µ∆

PE

µ∆

+

eV

AP

n-GaAs GaMnAs

P

Without Δμ

IS

V

totalµ∆

AP

16

No spin accumulation

( )( )

B

B

4 1 2d d tanh 2I

k T F eIFSV I eV k T

−= +

F : Fano factorT : electron temperature

No injection

Injection

17

P APS 2

S SS

P−

≡

P APC 2

S SS +≡

Charge current

Spin current

B, 4eV k Tµ> ∆

P APC 02 2

I IIµ µ

µ↑ ↓+ +

= ∝ −

( )P APS 2I II

Pµ µ↑ ↓

−= ∝ −

Eµ∆

+

eV

n-GaAs GaMnAs

( )PI V ( )API V

( )PS V

and

Current

Noise

and ( )APS V

reconstruct

0µ

µ↑µ↓

18

2C CS eI F=

Charge

2S SS eI F=

Spin

charge and spin tunnel through the barrier as a single objectSame Fano factor

19

2012/8/24 20

2eV µ∆<

Bk T µ> ∆

Tcryostat=1.6 K (140 μV)

Eµ∆

+

eV

n-GaAs GaMnAs

V P µ∆ = ∆

E

0.2µ∆ ≈

n-GaAsGaMnAs

meV

Spin injection process

200V >meV

V µ∆

Hot electrons

21

sampleµ∆

Spin accumulation

Spin flip process

E. G. Mishchenko, Physical Review B 68, 100409 (2003).

22

GaMnAs

E

µ∆

n-GaAs GaMnAs

F=0.5

F=1

PAP

23

Shot noise due to the spin current through a tunnelling barrier was detected

Our result indicates that charge and spin tunnel through the barrier as a single object

The electron temperature increase due to spin injection was quantitatively estimated

sensitive probe for spin transport

Spin current shot noise in various systems

v?C SF F≠

Spin orbit interactionMany body effectetc…

Cooling the electron temperature

v

Spin injection through metallic contactSuper conductor on the channel

Coherent phenomena of Spin current

heatSpin current

24

Shot noise induced by spin accumulationFirst experimental demonstration of shot noise induced by spin accumulation�Measuring Noise� =Measuring Current fluctuationThe noise is the signalShot noise in mesoscopic fieldスライド番号 6Spintronics via Shot noiseSpintronics via Shot noise (Theory)Shot noise induced by spin accumulationWhat is Spin current What’s happen in the Shot noise More general caseSample structureCharacteristic of the sampleSet up for shot noise measurementExpected signalMeasured noise SIHigh bias regionRelation between Noise and CurrentLow bias regionOrigin of over heatingWhat’s happen in the presence � of spin flip process Brief resultConclusion