The thermal Josephson effect, which occurs when heat is transported across a gap between two superconductors, has been measured in the lab for the first time. The experiment was done by two physicists in Italy and confirms a theoretical prediction made in 1965. As well as confirming the bizarre prediction that some heat flows from the cold side of the junction to the hot side, the breakthrough could further the development of thermal circuits that use heat in much the same way as charge is used in electronic devices.
The conventional Josephson effect was predicted in 1962 by the British physicist Brian Josephson and was observed in the lab less than a year later. The effect occurs in a Josephson junction, which is created when two superconductors are separated by a thin layer of non-superconducting material or free space. Josephson showed that Cooper pairs – paired electrons that experience no electrical resistance within superconductors – can tunnel across the junction. All of the Cooper pairs are in the same quantum state and are thus represented by the same wavefunction. The tunnelling current is a sinusoidal function of the phase difference of the wavefunction from one side of the gap to the other. As a result, a current of Cooper pairs will flow across the gap even if there is no applied voltage.
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