Collective Mode and Its Interaction with Electromagnetic Field in Superconducting Tunnel Junction

概要

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We investigate the properties of collective modes and their interaction with the electromagnetic field in a supercoducting tunnel junction. A microscopic calculation is performed by taking account of the tunneling and Coulomb interaction terms explicitly instead of using averaged terms as in previous works. The excitation energies of in- and out-of-phase collective modes are pushed up to finite values by the Coulomb interaction similarly to the plasma frequency in bulk superconductors, and the dispersion relation is also derived. The tunnel junction has different collective modes depending on the sites, and the absorption of microwave photons occurs at the interface between the superconductor and the insulating barrier. This dependence on sites is important in estimating the transition dipole moment, and the calculated result is much smaller than that obtained in phenomenological studies.
2012-04-15