Experimental observation of the Spin-Hall Effect in InGaN/GaN superlattices
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Transcript of Experimental observation of the Spin-Hall Effect in InGaN/GaN superlattices
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Experimental observation of the Spin-Hall Effect in InGaN/GaN sup
erlattices
Student : Hsiu-Ju, Chang
Advisor: Yang Fang, Chen
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Outline
• Introduction
1. Basic elements in Spin-Hall effect
2. Recent theoretical analysis
3. Experimental observation
• Experiment and discussion
• Summary
• Future work
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- Introduction - Basic elements in Spin-Hall effect
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- 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
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Red arrows : spin directionGreen arrows : moment a
E = 0
E = EX
xeEdt
Pdˆ
Rate at momentum space
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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
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spin Hall (SH) conductivity
Independent of both the Rashba coupling strength and of
the 2DES density.
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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.
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Recent theoretical analysis Ⅱ
G. Y. Guo, PRL V94 226601 (2005)
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G. Y. Guo, PRL V94 226601 (2005)
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G. Y. Guo, PRL V94 226601 (2005)
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G. Y. Guo, PRL V94 226601 (2005)
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G. Y. Guo, PRL V94 226601 (2005)Hole concentration = 0.1 e/cell
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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.
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- Introduction - Experimental observation
Reference:J. Wunderlich,B. Kaestner, J. Sinova, and T. Jungwirth PRL, V94, 047204 (2005)
pn
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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.
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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 ?• ........