SOME PHONON EFFECTS IN SUPERCONDUCTING TUNNEL JUNCTIONS

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Abstract
Tunneling measurements have been made on junctions consisting of aluminium separated from a second metal by aluminium oxide insulating layers. When the second metal was lead, tin, or indium, the effect of its phonon spectrum on the tunnel current was observed. Results with indium indicate that there is a broad group of phonons at an energy of 5 millivolts and another group at an energy of 13 millivolts in the indium phonon spectrum. The end point of the spectrum is at 14.8 ± 0.1 millivolts. Evidence is presented for a relationship between the strength of the phonon structure, the phonon energy, and the width of the superconducting energy gap from measurements on lead, tin, and indium. Measurements of the temperature dependence of the phonon structure in lead and indium are also reported.