diff --git a/superconductivity_assignment2_kvkempen.pdf b/superconductivity_assignment2_kvkempen.pdf index f7a9e49..78cf357 100644 Binary files a/superconductivity_assignment2_kvkempen.pdf and b/superconductivity_assignment2_kvkempen.pdf differ diff --git a/superconductivity_assignment2_kvkempen.tex b/superconductivity_assignment2_kvkempen.tex index 245dac2..819650f 100755 --- a/superconductivity_assignment2_kvkempen.tex +++ b/superconductivity_assignment2_kvkempen.tex @@ -199,16 +199,44 @@ We apply a gauge transformation as follows. \end{enumerate} \section{Type II superconductors and the vortex lattice} -\begin{em} +In 2003, Alexei Abrikosov was one of the winners of the Nobel Prize in Physics ``for pioneering contributions to the theory of superconductors and superfluids''. +For this occasion, he gave a lecture called ``Type II superconductors and the vortex lattice''\cite{abrikosov} +explaining the discoveries that led to the understanding of conventional superconductors. +To get started, let me first explain what superconductors are. + +% Begin copy from philosophy +Superconductors are characterized by perfect diamagnetism and zero resistance. +Perfect diamagnetism is the ability by superconductors to have a net zero magnetic field inside. +If you apply an external magnetic field, this thus means that a superconductor will let a current flow on its inside to generate a field to counteract this external field $\vec{H}$. +This generated current is called a supercurrent. +This is, however, a phase of the material. +Superconductors only have these properties below a certain temperature, its critical temperature $T_c$, and can only expel a maximum external magnetic field, its critical magnetic field $B_c(T)$, which is a function of the temperature. + +The class of superconductors we have a model for, is the class of conventional superconductors, which are explained by a theory called BCS (and some extensions). +In this class, there are two types, called type-I and type-II superconductors. +% End copy from philosophy + +In type-I superconductors, there is only one phase in which the superconductor material exhibits perfect diamagnetism: +when the externally applied magnetic field $H < B_c(T)$ and $T < T_c$. + +In type-II superconductors, there are two phases distinct from the normal conducting state. +One is the superconducting state which behaves as in type-I superconductors, with critical field $B_{c1}(T)$. +This state is reached for $T < T_c$ and $B_E < B_{c1}(T)$. +The other state is a mixed state that allows some flux to pass through the material. +This passing through is done by creating normally conducting channels throughout the material where a fixed amount of flux can pass through. +This fixed amount is a multiple of the flux quantum $\Phi_0$. +The material generates current around these channels cancelling the field on the inside of the superconducting part of the material. + +--- + The nobel prize lecture by Abriskosov \cite{abrikosov} was really interesting. -The start was a good recap of the breakthroughs relevant to conventional superconductivity,\footnote{Why is that every story on superconductivity includes KGB captivity?} +The start was a good recap of the breakthroughs relevant to conventional superconductivity,\footnote{Why is it that every story on superconductivity includes KGB captivity?} but in pages 61--63, the theory is worked through a little quickly. I might reread it some times. -\end{em} -\todo{The essay so far is just a draft. Choosing a topic was hard.} +\todo{The essay so far is just a draft. Choosing a topic was hard. As we are to aim at bachelor students not knowing sc, I thought a proper introduction was appropriate.} \section{Currents inside type-II superconducting cylinder} For $B_{c1} < B_E < B_{c2}$, the cylinder of type-II superconductor material is in the mixed state.