Skip to content

Commit

Permalink
[tex] more polishing
Browse files Browse the repository at this point in the history
  • Loading branch information
moritz committed Dec 17, 2009
1 parent 579339b commit 968aa66
Show file tree
Hide file tree
Showing 15 changed files with 615 additions and 515 deletions.
Binary file modified tex/adapting-pic.pdf
Binary file not shown.
473 changes: 247 additions & 226 deletions tex/adapting.svg
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
Binary file added tex/beamsplitter2.jpg
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
16 changes: 16 additions & 0 deletions tex/bib.bib
Expand Up @@ -164,6 +164,22 @@ @article{datta-das
doi = {10.1063/1.102730} doi = {10.1063/1.102730}
} }


@Article{ishe-ew,
title = {Charge Hall effect driven by spin-dependent chemical potential gradients and Onsager relations in mesoscopic systems},
author = {Hankiewicz, E. M. and Li, Jian and Jungwirth, Tomas and Niu, Qian and Shen, Shun-Qing and Sinova, Jairo },
journal = {Phys. Rev. B},
volume = {72},
number = {15},
pages = {155305},
numpages = {5},
year = {2005},
month = {Oct},
doi = {10.1103/PhysRevB.72.155305},
publisher = {American Physical Society}
}



@article{ISHE, @article{ISHE,
author = {E. Saitoh and M. Ueda and H. Miyajima and G. Tatara}, author = {E. Saitoh and M. Ueda and H. Miyajima and G. Tatara},
collaboration = {}, collaboration = {},
Expand Down
Binary file modified tex/comparison-over-phi.pdf
Binary file not shown.
6 changes: 3 additions & 3 deletions tex/intro.tex
Expand Up @@ -42,7 +42,7 @@ \chapter{Introduction}


However, building ferromagnetic contacts or devices on However, building ferromagnetic contacts or devices on
the nano scale is a serious technological challenge, and combining millions of the nano scale is a serious technological challenge, and combining millions of
ferromagnetic structures on a single seems hardly possible. ferromagnetic structures on a single device seems hardly possible.


In this Diploma Thesis, we therefore investigate how a spin polarized electron In this Diploma Thesis, we therefore investigate how a spin polarized electron
beam can be achieved by using only non-magnetic materials. The Rashba beam can be achieved by using only non-magnetic materials. The Rashba
Expand All @@ -64,15 +64,15 @@ \chapter{Introduction}
experimentally accessible in quantum wells at heterojunctions in GaAs, experimentally accessible in quantum wells at heterojunctions in GaAs,
HgTe and other semiconductors. HgTe and other semiconductors.


In chapter \ref{sec:theory} we present the basic theoretical underpinning for In Chapter \ref{sec:theory} we present the basic theoretical underpinning for
the calculations to come: the Landauer Formula which relates conductance to the calculations to come: the Landauer Formula which relates conductance to
the transmission matrix $T$, the Fisher-Lee relation which allows calculation the transmission matrix $T$, the Fisher-Lee relation which allows calculation
of $T$ based on the Green's function in sample and lead, the Rashba-Bychkov of $T$ based on the Green's function in sample and lead, the Rashba-Bychkov
spin-orbit coupling which causes all the interesting effects discussed in this spin-orbit coupling which causes all the interesting effects discussed in this
thesis, and finally we present a tight binding model which allows numerical thesis, and finally we present a tight binding model which allows numerical
calculation of the Green's functions and thus $T$. calculation of the Green's functions and thus $T$.


In chapter \ref{sec:analytical} we present an analytical model of an electron In Chapter \ref{sec:analytical} we present an analytical model of an electron
wave traveling from a normal region to a region with spin-orbit coupling. The wave traveling from a normal region to a region with spin-orbit coupling. The
wave is decomposed into two parts of opposite chirality, and we wave is decomposed into two parts of opposite chirality, and we
analyze the transmission and reflection coefficients resolved by chirality. analyze the transmission and reflection coefficients resolved by chirality.
Expand Down
16 changes: 12 additions & 4 deletions tex/khodas.tex
Expand Up @@ -222,7 +222,7 @@ \section{Interface Between Normal and Spin-Orbit Coupling Regions}
it follows that it follows that


\begin{align} \begin{align}
\phi_c &= -\sin ^{-1}\left(a-\sqrt{a^2+1}\right) \phi_c &= -\sin ^{-1}\left(\ta-\sqrt{\ta^2+1}\right)
\end{align} \end{align}


Figure \ref{fig:critical-angle} shows the critical angle as a function Figure \ref{fig:critical-angle} shows the critical angle as a function
Expand Down Expand Up @@ -307,14 +307,22 @@ \section{Generalization to two Spin-Orbit Regions}
\ref{fig:plots-nonzero}, and in the region $\phi < \phi+_{B,c}$ the various transmission and reflection \ref{fig:plots-nonzero}, and in the region $\phi < \phi+_{B,c}$ the various transmission and reflection
coefficients look very similar to the case with $\ta_A = 0$. coefficients look very similar to the case with $\ta_A = 0$.


The second gray line is critical angle $\phi^+_{c2}$ associated with The second gray line is the critical angle $\phi^+_{c2}$ associated with
$\ta_A$. For $\ta_A$. For
$\phi > \phi^+_{A,c}$ the momentum in $x$ direction $p_{x,A}$ is again $\phi > \phi^+_{A,c}$ the momentum in $x$ direction $p_{x,A}$ is again
imaginary, just like if we had another interface to a normal region imaginary, just like if we had another interface to a normal region
left of the $A$ region. left of the $A$ region.


It follows the same $\ta$ dependency, namely $\phi^+_{c2} = $p_{x,A}$ has the same structural dependence on $\ta_A$ as $p_{x,B}$
-\sin^{-1}(\ta_A - \sqrt{1+\ta_A^2})$. has on $\ta_B$:

\begin{align}
p_{x,A}^+ = \sqrt{ p_A^2 - p_z^2} = p \sqrt{(\sqrt{1+\ta_A^2} -
\ta_A)^2 - \sin^2 \phi^+}
\end{align}

It follows that $\phi^+_{c2}$ has a similar form as $\phi^+_{c1}$,
namely $\phi^+_{c2} = -\sin^{-1}(\ta_A - \sqrt{1+\ta_A^2})$.


% %
%\begin{figure} %\begin{figure}
Expand Down
23 changes: 16 additions & 7 deletions tex/numerics.tex
Expand Up @@ -287,7 +287,14 @@ \subsection{Comparison to Analytical Results}
\begin{center} \begin{center}
\includegraphics[width=0.8\textwidth]{adapting-pic.pdf} \includegraphics[width=0.8\textwidth]{adapting-pic.pdf}
\end{center} \end{center}
\caption{Injecting one spin-up charge carrier into the system} \caption{Injecting one spin-up charge carrier into the system notionally
splits up the wave into two wave functions with $+$ and $-$ chirality.
At the interface a part of the wave is scattered, and
$\mathbf{\psi^\pm}$
describe the injected and reflected wave functions left of the
interface. The transmitted fraction of the wave function is then
projected onto the $\uparrow,\downarrow$ bases when it reaches the right
lead.}
\end{figure} \end{figure}


% Since there is no dissipation in our model, and we assume that the mere % Since there is no dissipation in our model, and we assume that the mere
Expand Down Expand Up @@ -438,7 +445,7 @@ \subsection{Comparison to Analytical Results}
(figure \ref{fig:n-so-rel}). (figure \ref{fig:n-so-rel}).


To understand better why we don't get a very clear picture of the critical To understand better why we don't get a very clear picture of the critical
angle the numerical results, we look at \ref{eq:a-n-left} and for a moment angle, we look at \ref{eq:a-n-left} and for a moment
ignore the global phases that the $\exp$ functions provide, and obtain a ignore the global phases that the $\exp$ functions provide, and obtain a
simplified expression for $a$ and $b$. simplified expression for $a$ and $b$.


Expand All @@ -457,7 +464,7 @@ \subsection{Comparison to Analytical Results}
T_{2\uparrow,1\uparrow} &\approx \left|a \chi_{SO}^{+U} t_{++} T_{2\uparrow,1\uparrow} &\approx \left|a \chi_{SO}^{+U} t_{++}
+ b \chi_{SO}^{-U} t_{--} \right|^2\nonumber\\ + b \chi_{SO}^{-U} t_{--} \right|^2\nonumber\\
T_{2\downarrow,1\downarrow} &\approx \left|c \chi_{SO}^{-D} t_{--} T_{2\downarrow,1\downarrow} &\approx \left|c \chi_{SO}^{-D} t_{--}
+ d \chi_{SO}^{+D} t_{--} \right|^2 + d \chi_{SO}^{+D} t_{++} \right|^2
\label{eq:simplfied-t} \label{eq:simplfied-t}
\end{align} \end{align}


Expand Down Expand Up @@ -533,19 +540,21 @@ \section{Relation to experiments}
\begin{center} \begin{center}
\includegraphics[width=0.7\textwidth]{beamsplitter2.jpg} \includegraphics[width=0.7\textwidth]{beamsplitter2.jpg}
\end{center} \end{center}
\caption{Experimental realization of a beam splitter, with two \caption{Experimental realization of a beam splitter in a HgTe/CdTe quantum
well, with two
collimating quantum point contact on top and bottom. In the middle collimating quantum point contact on top and bottom. In the middle
there is a strip at angle $\phi = 45^\circ$ where an electric field there is a strip at angle $\phi = 45^\circ$ where an electric field
can be applied by a gate. Image courtesy of M. Mühlbauer, can be applied by a gate. Image courtesy of M. Mühlbauer,
Physikalisches Institut, Universität Würzburg} Physikalisches Institut, Universität Würzburg\cite{mathias}}
\label{fig:experiment} \label{fig:experiment}
\end{figure} \end{figure}


It is possible to realize interfaces between two spin-orbit coupling regimes It is possible to realize interfaces between two spin-orbit coupling regimes
in experiments. Figure \ref{fig:experiment} shows such a sample as produced in experiments. Figure \ref{fig:experiment} shows such a sample as produced
by the group of H. Buhmann in our department \cite{mathias}. by the group of H. Buhmann in our department \cite{mathias}.


It has two wide contacts on the left and right side, and two collimating point It consists of a two-dimensional electron gas in a HgTe/CdTe quantum well. It has
two wide leads on the left and right side, and two collimating point quantum
contacts on the top and bottom. At an angle of $45^{\circ}$ there is a stripe contacts on the top and bottom. At an angle of $45^{\circ}$ there is a stripe
across the sample. Inside the strip the electric field, and thus the strength across the sample. Inside the strip the electric field, and thus the strength
of the spin-orbit coupling strength can be tuned by a gate electrode that is of the spin-orbit coupling strength can be tuned by a gate electrode that is
Expand All @@ -558,7 +567,7 @@ \section{Relation to experiments}
scatters electrons too. scatters electrons too.


The spin polarization can be measured via the Inverse Spin-Hall Effect The spin polarization can be measured via the Inverse Spin-Hall Effect
\cite{ISHE} as an electrical current. \cite{ishe-ew,ISHE} as an electrical current.


%For $\phi > \phi_c$, the wave $\exp{i p_x^+ x}\exp{i p_z z} t_{++}\chi_{SO}^+$ %For $\phi > \phi_c$, the wave $\exp{i p_x^+ x}\exp{i p_z z} t_{++}\chi_{SO}^+$
%does not propagate, because $p_x^+$ is imaginary. That means that the relative %does not propagate, because $p_x^+$ is imaginary. That means that the relative
Expand Down
Binary file added tex/rashba-dispersion.jpg
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
Binary file modified tex/setup-simple.pdf
Binary file not shown.

0 comments on commit 968aa66

Please sign in to comment.