Transcript Experimental observation of the Spin

Experimental observation of the
Spin-Hall Effect in InGaN/GaN
superlattices
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

P 2 2 
H

  zˆ  p 
2m
h
 : Rashba Coupling constant

 : Pauli Matrices
m : Electron Effect Mass
zˆ : unit vector perpendicular to 2 DES plane
Red arrows : spin direction
Green arrows : moment a
E=0
Rate at momentum space

dP
 eExˆ
dt
E = EX
spin current in the y direction
A
where pF+ and pF- are the Fermi momenta of the majority
and minority spin Rashba bands.
When
n2D > (mmλ^2)/(π(2πh)^4)
A = 2mλ(2πh)
spin Hall (SH) conductivity
Independent of both the Rashba coupling strength
and of
the 2DES density.
Recent theoretical analysis Ⅰ
summary
• 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)
Hole concentration = 0.1 e/cell
G. Y. Guo, PRL V94 226601 (2005)
Recent theoretical analysis Ⅱ
summary
• 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)
n
p
Experimental observation
summary
• 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,
such as nitride materials ?
• The theoretical calculation reveals that the SHE can
be 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 ?
• ........