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main.tex
69
main.tex
@@ -242,6 +242,75 @@ We can look at the Nam conductivity now:
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As there is as yet no filtering based on the free energy, this is messy, so the comparison to \cref{fig:osRepro1b} is necessary to see which combinations of $T$ and $n$ are valid.
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However, this is still quite numerically unstable, even with the dimensional reduction procedure described above for $n$ and $\corr$.
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The information that higher $n$ leads to lower $\sigma$ is expected, and does suggest that the implementation is correct, although still very noisy.
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\section{Noise calculation}
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For our noise calculation, we assume a material parameterised by a Debye frequency $\debye$ and the interaction parameter $N(0) V$.
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Because these aren't necessarily experimentally accessible, I tried to keep their values such that they lead to a physically reasonable $T_c$.
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In order to keep $N(0) V$ small and $\debye$ bigger than the other parameters, I chose $N(0)V = 0.25$ and $\debye = \SI{1e13}{\per\s}$.
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This leads to $T_{c0} = T_c(\mu = 0) = \SI{1.44e11}{\per\s}$, similar to the values used for the equilibrium Nam case.
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Because that particular choice of $N(0) V$ and $\debye$ lead to some additional numerical noise for $T$ close to $T_c$, I changed the values slightly to $N(0) V = 0.2$ and $\debye = \SI{1e14}{\per\s}$, which leads to $T_{c0} = \SI{7.64e11}{\per\s}$, and ensures the graphs below look good for $T > 0.8 T_c$.
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\begin{enumerate}
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\item Use the Owen Scalapino coupled integral equations \cref{eq:gap,eq:n}, find $\mu$ and $\Delta$ for fixed $n$.
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\item Find the expected gap from the approximation in OS, $T_c(n) \approx (1 - 4n) T_{c0}$.
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If $T > T_c(n)$, then the calculation is skipped (a more complete handling would use either the Lindhard form or use a Nam expression that's been extended to $\Delta = 0$).
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This is necessary because the coupled integral equations are very hard to solve
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\item Using the modified Nam equations, calculate the dielectric function and create the approximated interpolation form, similar to the equilibrium case.
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\item Calculate the noise as usual.
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\end{enumerate}
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\subsection{Figures}
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Some examples of the noise are potrayed below, from \crefrange{fig:smallomeganoise}{fig:largerTnoise}.
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There are some interesting features in the graphs:
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\begin{itemize}
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\item In the curves for constant omega, \crefrange{fig:smallomeganoise}{fig:bigomeganoise}, there seems to be a consistent dip, where initially as $T$ increases, the noise decreases.
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That seems like it could be an artifact of the method used to calculate $\Delta$, but it is very odd (because nothing besides $\Delta$) should affect any other step.
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\item In the constant omega graphs, for $n = .02$ and $n = .04$ the noise is greater than for $n = 0$ even in the region where it goes to the `normal state'.
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This is confusing.
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\item Most values of $n$ should not be superconducting for most of the range of $T$, as expected.
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Near the critical temperature for a particular $n$, the noise increases as expected, showing a little gap.
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See \cref{fig:mediumTnoise}.
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\end{itemize}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constOmega1/1}
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\caption{$T_1$ vs temperature, for very small omega} \label{fig:smallomeganoise}
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\end{figure}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constOmega1/10}
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\caption{$T_1$ vs temperature, for medium omega} \label{fig:mediumomeganoise}
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\end{figure}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constOmega1/13}
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\caption{$T_1$ vs temperature, for big omega} \label{fig:bigomeganoise}
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\end{figure}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constT1/43}
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\caption{$T_1$ vs frequency, for a temperature where all the chosen $n$ values are allowed, showing the gap between $n = 0$ and $n > 0$, which seems potentially spurious.} \label{fig:smallTnoise}
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\end{figure}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constT1/35}
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\caption{$T_1$ vs frequency, for a temperature where the $n = .04$ state is almost, but not quite surpressed.} \label{fig:mediumTnoise}
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\end{figure}
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\begin{figure}[htp]
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\centering
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\includegraphics[width=14cm]{constT1/15}
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\caption{$T_1$ vs frequency, for temperature so large that only the $n = 0$ state is energetically allowed to be superconducting} \label{fig:largerTnoise}
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\end{figure}
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\printbibliography
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\end{document}
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