The Josephson Junction — A New Tunable Phonon Source with High-Frequency Resolution
Several methods of monochromatic phonon generation have been presented in the past, like piezoelectric surface excitation, microwave  or optical  pumping of impurity ions, and single-particle tunneling in superconducting junctions [4,5]. Of these methods, tunneling junctions have the advantage of being independent of the sample under study. On single-particle tunneling, “bremsstrahlung” phonons are generated which can be made quasi monochromatic by a modulation technique .Their frequency, f = (eV-2Δ)/h, is tunable by the applied voltage V. Their frequency resolution depends on the sharpness of the energy gap Δ, usually a few percent. The energy gap comes into play because Cooper pairs are being broken during the single particle tunneling process. If the pairs could be left intact, i.e. if Josephson tunneling  could be used for phonon generation, one should obtain a much higher frequency resolution. We have recently observed that it is indeed possible to generate monochromatic phonons by the Josephson effect, so that very high resolution spectroscopy is now feasible. The present paper accounts for the results now available on the generation process. The first application to high-resolution spectroscopy is presented in a following paper by Schick et al..
KeywordsMicrowave Recombination Boron Resis Acoustics
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