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Perturbing nano-junctions with microwaves reveals their character


Perturbing nano-junctions with microwaves reveals their character

 

The most remarkable property of superconductors is their ability to carry electrical current without energy dissipation. This property holds also for a nanostructure made of a normal metal (“N”, not superconducting) between two superconducting contacts (S), provided the N conductor is short enough. In such a system the critical current, i.e. the largest non-dissipative current the SNS structure can sustain, is determined by the length and electrical resistance of the normal metal, in the absence of the superconducting contacts.

 

Beyond the critical current, energy is dissipated in the normal metal, and the current has to be lowered below a certain value called the retrapping current (generally lower than the critical current) for the dissipation to vanish. The reason why the retrapping current differs from the critical current is an open question related to dynamics of quantum transport in the junction.

 

The influence of a microwave excitation in the range 10 MHz – 40 GHz on both the critical and the retrapping currents reveals two well separated timescales: the critical current is related to the elastic scattering of the electrons in the normal metal, whereas the retrapping current is sensitive to inelastic processes, in particular the electron-phonon interaction in the temperature range that has been explored.

 

SNS junctions are used in superconducting electronics. The understanding of the dynamics of quantum transport in such junctions may open new routes to design fast devices, such as low impedance detectors.

 

Reference : F. Chiodi, M. Aprili, B. Reulet, Phys. Rev. Lett. 103, 177002 (2009)

 

Contact : Bertrand Reulet (reulet@lps.u-psud.fr)