{tag=Josephson effect}

To <Brian Josephson> for the prediction of the <Josephson effect>.


1973 Nobel Prize in Physics

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{{wiki=Josephson_effect#History}}

In 1962 <Brian Josephson> published his inaugural paper predicting the effect as <Possible new effects in superconductive tunnelling>{full}.

In 1963 <Philip W. Anderson> and <John M. Rowell> published their paper that first observed the effect as <Possible new effects in superconductive tunnelling>{full}.

Some golden notes can be found at <True Genius: The Life and Science of John Bardeen> page 224 and around. <Philip W. Anderson> commented:
> We were all - <Brian Josephson>[Josephson], Pippard and myself, as well as various other people who also habitually sat at the <Mond Laboratory>[Mond] tea and participated in the discussions of the next few weeks - very much puzzled by the meaning of the fact that the <electric current>[current] depends on the <Josephson phase>[phase]

As part of the course Anderson had introduced the concept of broken symmetry in superconductors. Josephson "was fascinated by the idea of broken symmetry, and wondered whether there could be any way of observing it experimentally."


History of the Josephson effect

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<Discrete> <quantum> effect observed in <superconductors> with a small insulating layer, a device known as a <Josephson junction>.

To understand the behaviour effect, it is important to look at the <Josephson equations> consider the following <Josephson effect regimes> separately:
* <DC Josephson effect>
* <AC Josephson effect>
* <Inverse AC Josephson effect>

A good summary from Wikipedia by physicist Andrew Whitaker:
> at a junction of two superconductors, a current will flow even if there is no drop in voltage; that when there is a voltage drop, the current should oscillate at a frequency related to the drop in voltage; and that there is a dependence on any magnetic field

Bibliography:
* https://www.youtube.com/watch?v=cnZ6exn2CkE "Superconductivity: Professor <Brian Josephson>". Several random excerpts from Cambridge people talking about the Josephson effect


Josephson effect

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Two equations derived <from first principles> by <Brian Josephson> that characterize the device, somewhat like an <I-V curve>:
$$
I(t) = I_c \sin (\varphi (t)) \\
\dv{\varphi(t)}{t} = \frac{2 e V(t)}{\hbar}
$$
where:
* $I_c$: <Josephson current>
* $\varphi$: the <Josephson phase>, a function $\R \to \R$ defined by the second equation plus initial conditions
* $V(t)$: input voltage of the system
* $I(t)$: current across the junction, determined by the input voltage

Note how these equations are not a typical <I-V curve>, as they are not an instantaneous dependency between voltage and current: the history of the voltage matters! Or in other words, the system has an internal state, represented by the <Josephson phase> at a given point in time.

To understand them better, it is important to look at some important cases separately:
* <AC Josephson effect>: V is a fixed <DC voltage>


Ciro Santilli @cirosantilli 34

 Incoming links: Brian Josephson