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Author SHA1 Message Date
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
d4772ce40a Merges 2021-03-18 20:06:42 -05:00
83af11d3a2 fix bad braces 2021-03-18 20:02:16 -05:00
6a3818df4a Adds plot for conductivity 2021-02-15 16:59:32 -06:00

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@@ -197,7 +197,7 @@ We can keep the same expressions as earlier with the same reduced dimensionless
\end{align}
And then our expression, with the changes becomes:
\begin{equation}
\sigma(\kappa, \xi) = -i \frac{3 \sigma_0}{4} \frac{1}{\xi}\left[\int_{1 - \xi}^{1}\dd{\xi} \tanh(\frac{\xi + \xi' - \mu}{2 t}) I_1 + \int_{1}^{\infty} \dd{\xi'} \left( \tanh(\frac{\xi + \xi' - \mu}{2t}) I_1 - \tanh(\frac{\xi' - \mu}{2t})I_2 \right) \right]
\sigma(\kappa, \xi) = -i \frac{3 \sigma_0}{4} \frac{1}{\xi}\left[\int_{1 - \xi}^{1}\dd{\xi} \tanh(\frac{\xi + \xi' - \mu}{2 t}) I_1 + \int_{1}^{\infty} \dd{\xi'} \left( \tanh(\frac{\xi + \xi' - \mu}{2t}) I_1 - \tanh(\frac{\xi' - \mu}{2t})I_2 \right) \right] \label{eq:nam}
\end{equation}
with
\begin{align}
@@ -210,6 +210,39 @@ with
g &= \frac{\xi' \left( \xi + \xi'\right) + 1}{\sqrt{\xi'^2 - 1}\sqrt{(\xi + \xi')^2 - 1}}
\end{align}
\section{Mathematica implementation}
We want to dimensionally reduce these when we implement the code, by writing $\corr$, $\Delta$, $\omega_D$ and $T$ in units of $\Delta_0$:
\begin{align}
o_D &= \frac{\omega_D}{\Delta_0} \\
m &= \frac{\corr}{\Delta_0} \\
d &= \frac{\Delta}{\Delta_0} \\
t &= \frac{T}{\Delta_0}
\end{align}
giving us
\begin{equation}
\left[ N(0) V \right]^{-1} = \int_{- o_D}^{o_D} \frac{\dd{\varepsilon}}{\sqrt{d^2 + \varepsilon^2}} \tanh{\frac{\sqrt{d^2 + \varepsilon^2} - m}{2 t}}
\end{equation}
\begin{equation}
n = \int_0^\infty \dd{\epsilon} \left( \frac{1}{1 + \exp(\frac{\sqrt{d + \varepsilon^2} - m}{t})} - \frac{1}{1 + \exp(\frac{\sqrt{d^2 + \varepsilon^2}}{t})} \right)
\end{equation}
We can look at the Nam conductivity now:
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{realpartofconductivity}
\caption{$\frac{\Re[\sigma_{SC}]}{\sigma_N}$} \label{fig:real}
\end{figure}
\begin{figure}[htp]
\centering
\includegraphics[width=14cm]{imagpartofconductivity}
\caption{$\frac{\Im[\sigma_{SC}]}{\sigma_N}$} \label{fig:imag}
\end{figure}
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 $N(0) V$.
@@ -217,6 +250,8 @@ Because these aren't necessarily experimentally accessible, I tried to keep thei
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, $T_c(n) \approx (1 - 4n) T_{c0}$.
@@ -226,6 +261,56 @@ This leads to $T_{c0} = T_c(\mu = 0) = \SI{1.44e11}{\per\s}$, similar to the val
\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}