\sect{Heat Capcity of He4 system, energy gap}

%Baruch's  B04.

The specific heat of ${He^{4}}$ at low temperatures has the form
\[ \ C_{v}= AT^{3} + B(T)e^{- \Delta/ k_{B}T}\]
\begin{itemize}
\item [(a)]
What can you deduce about the excitations of the system?
(assume the the density of states of these excitations has the form
${N( \epsilon)\sim \epsilon ^{p}}$ as ${\epsilon\rightarrow
0}$.)
\item [(b)]
What would be the form of ${C_{v}}$ for a similiar system in
a two dimensional world?\\
\end{itemize}

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