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Master's Dissertation
DOI
10.11606/D.76.2009.tde-11092009-145126
Document
Author
Full name
Marco Antonio de Oliveira Hachiya
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2009
Supervisor
Committee
Menezes, Jose Carlos Egues de (President)
Silva, Erasmo Assumpção de Andrada e
Xavier, Jose Candido
Title in Portuguese
Efeito Hall de spin em poços quânticos com acoplamento spin-órbita inter-subbanda
Keywords in Portuguese
Spintrônica . Efeito Hall de spin . Interação spin-órbita
Abstract in Portuguese
A partir da teoria de resposta linear (formalismo de Kubo) calculamos a condutividade de spin $\sigma_^$ para um gás bidimensional de elétrons formado num poço quântico com duas subbandas devido a atuação de um novo tipo de interação spin-órbita [Bernardes et al. \textit{Phys. Rev. Lett.} \textbf, 076603 (2007) \& Calsaverini \textit{et al}. \textit{Phys. Rev. B} \textbf, 155313 (2008)]. Este novo termo é não-nulo mesmo em estruturas simétricas e surge devido ao acoplamento entre os estados confinados no poço de paridades diferentes. Encontramos um valor para $\sigma_^$ não-nulo e não-universal (dependente da intensidade do acoplamento $\eta$) quando somente uma das subbandas está ocupada, ao contrário de Rashba. Para encontrarmos valores realistas para $\sigma_^$, determinamos $\eta$ via cálculo autoconsistente. Esse cálculo é executado para diferentes valores de densidade eletrônica em poços simples e duplos. Obtivemos que $\sigma_^$ possui um comportamento não-monótono e sofre inversão de sinal como função da energia de Fermi (densidade de elétrons) conforme ela varia entre as duas subbandas. Contudo nossos resultados indicam que a condutividade Hall de spin é muito pequena $\left(``\ll \frac{8\pi}"ight)$ nesses sistemas (poços simples e duplos) e possivelmente não mensurável.
Title in English
Spin Hall effect in quantum wells with intersubband spin-orbit coupling
Keywords in English
Spintronics . Spin Hall Effect . Spin-orbit interaction.
Abstract in English
Using the Kubo linear response theory, we investigate spin Hall conductivity $\sigma_^$ in a two-dimensional electron gas in quantum wells with two subbands, when intersubband-induced spin-orbit coupling is operative [Bernardes et al. \textit{Phys. Rev. Lett.} \textbf, 076603 (2007) \& Calsaverini \textit{et al}. \textit{Phys. Rev. B} \textbf, 155313 (2008)]. This new spin-orbit term is non-zero even in symmetric structures and it arises from the distinct parity of the confined states. We find non-zero and non-universal $\sigma_^$ (dependent on spin-orbit coupling strength $\eta$) when only one of the subbands is occupied. This is in contrast to the Rashba spin-orbit interaction for which $\sigma_^$ is identically zero. To obtain realistic values for $\sigma_^$, we develop a self-consistent scheme to calculate $\eta$. We performed this calcultion for different values of the eletronic density in single and double wells. We find that $\sigma_^$ shows a non-monotonic behavior and a sign change as the Fermi energy (carrier density) varies between the two subband edges. However, our results indicate that $\sigma_^$ is extremely small $\left(``\ll \frac{8\pi}"ight)$ and possibly not measurable.
 
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Publishing Date
2009-09-22
 
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