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bafb0bc56c Add note about new NV 2021-04-05 09:47:49 -05:00
b779b4b66b updated figures and comments 2021-04-05 09:44:09 -05:00
bd177f215a Adds figures 2021-03-19 09:56:48 -05:00
36a10f224d Adds noise calculation again where'd it go 2021-03-18 20:07:33 -05:00

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@@ -242,6 +242,75 @@ We can look at the Nam conductivity now:
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.
However, this is still quite numerically unstable, even with the dimensional reduction procedure described above for $n$ and $\corr$.
The information that higher $n$ leads to lower $\sigma$ is expected, and does suggest that the implementation is correct, although still very noisy.
\section{Noise calculation}
For our noise calculation, we assume a material parameterised by a Debye frequency $\debye$ and the interaction parameter $N(0) V$.
Because these aren't necessarily experimentally accessible, I tried to keep their values such that they lead to a physically reasonable $T_c$.
In order to keep $N(0) V$ small and $\debye$ bigger than the other parameters, I chose $N(0)V = 0.25$ and $\debye = \SI{1e13}{\per\s}$.
This leads to $T_{c0} = T_c(\mu = 0) = \SI{1.44e11}{\per\s}$, similar to the values used for the equilibrium Nam case.
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 $T > 0.8 T_c$.
\begin{enumerate}
\item Use the Owen Scalapino coupled integral equations \cref{eq:gap,eq:n}, find $\mu$ and $\Delta$ for fixed $n$.
\item Find the expected gap from the approximation in OS, $T_c(n) \approx (1 - 4n) T_{c0}$.
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 $\Delta = 0$).
This is necessary because the coupled integral equations are very hard to solve
\item Using the modified Nam equations, calculate the dielectric function and create the approximated interpolation form, similar to the equilibrium case.
\item Calculate the noise as usual.
\end{enumerate}
\subsection{Figures}
Some examples of the noise are potrayed below, from \crefrange{fig:smallomeganoise}{fig:largerTnoise}.
There are some interesting features in the graphs:
\begin{itemize}
\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.
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.
\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'.
This is confusing.
\item Most values of $n$ should not be superconducting for most of the range of $T$, as expected.
Near the critical temperature for a particular $n$, the noise increases as expected, showing a little gap.
See \cref{fig:mediumTnoise}.
\end{itemize}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constOmega1/1}
\caption{$T_1$ vs temperature, for very small omega} \label{fig:smallomeganoise}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constOmega1/10}
\caption{$T_1$ vs temperature, for medium omega} \label{fig:mediumomeganoise}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constOmega1/13}
\caption{$T_1$ vs temperature, for big omega} \label{fig:bigomeganoise}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constT1/43}
\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}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constT1/35}
\caption{$T_1$ vs frequency, for a temperature where the $n = .04$ state is almost, but not quite surpressed.} \label{fig:mediumTnoise}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{constT1/15}
\caption{$T_1$ vs frequency, for temperature so large that only the $n = 0$ state is energetically allowed to be superconducting} \label{fig:largerTnoise}
\end{figure}
\printbibliography
\end{document}