Experimental observation of the Spin-Hall Effect in InGaN/GaN sup

erlattices

Student : Hsiu-Ju, Chang

Advisor： Yang Fang, Chen

Outline

• Introduction

1. Basic elements in Spin-Hall effect

2. Recent theoretical analysis

3. Experimental observation

• Experiment and discussion

• Summary

• Future work

- Introduction - Basic elements in Spin-Hall effect

- Introduction - Recent theoretical analysis Ⅰ

The hamiltonian of a 2DEG with Rashba spin coupling

planeDEStolarperpendicuvectorunitz

MassEffectElectronm

MatricesPauli

tconsCouplingRashba

pzhm

PH

2:ˆ

:

:

tan:

ˆ2

2

2

Red arrows : spin directionGreen arrows : moment a

E = 0

E = EX

xeEdt

Pdˆ

Rate at momentum space

spin current in the y direction

where pF+ and pF- are the Fermi momenta of the majorityand minority spin Rashba bands.

When

n2D > (mmλ^2)/(π(2πh)^4)

A = 2mλ(2πh)

A

spin Hall (SH) conductivity

Independent of both the Rashba coupling strength and of

the 2DES density.

Recent theoretical analysis Ⅰsummary

• We describe a new effect in semiconductor spintronics that leads to dissipationless spin currents in paramagnetic spin-orbit coupled systems.

• We argue that in a high-mobility two-dimensional electron system with substantial Rashba spin-orbit coupling, a spin current that flows perpendicular to the charge current is intrinsic.

• In the usual case where both spin-orbit split bands are occupied, the intrinsic spin-Hall conductivity has a universal value for zero quasiparticle spectral broadening.

Recent theoretical analysis Ⅱ

G. Y. Guo, PRL V94 226601 (2005)

G. Y. Guo, PRL V94 226601 (2005)

G. Y. Guo, PRL V94 226601 (2005)

G. Y. Guo, PRL V94 226601 (2005)

G. Y. Guo, PRL V94 226601 (2005)Hole concentration = 0.1 e/cell

Recent theoretical analysis Ⅱsummary

• The calculated orbital-angular momentum (orbital) Hall conductivity is one order of magnitude smaller, indicating no cancellation between the spin and orbital Hall effects in bulk semiconductors.

• Furthermore, it is found that the spin Hall effect can be strongly manipulated by strains.

- Introduction - Experimental observation

Reference:J. Wunderlich,B. Kaestner, J. Sinova, and T. Jungwirth PRL, V94, 047204 (2005)

pn

Experimental observationsummary

• When an electric field is applied across the hole channel, a nonzero out-of-plane component of the angular momentum is detected whose sign depends on the sign of the electric field and is opposite for the two edges.

• Microscopic quantum transport calculations show only a weak effect of disorder, suggesting that the clean limit spin-Hall conductance description (intrinsic spin-Hall effect) might apply

to our system.

Motivation • The SHE has been observed by Wunderlich et al. and

Kato et al. for GaAs semiconductor.• Can the SHE be observed in other semiconductors, su

ch as nitride materials ? • The theoretical calculation reveals that the SHE can b

e tuned by strains, but there is no experimental evidence to prove it.

• The difference of the SHE on external current has not been varified.

• What will be the influence of temperature on the SHE ?• ........