Nature of response to electromagnetic radiation in contacts with superconducting oxides

The response of point contacts of tantalum, copper and niobium with the YBa2Cu3O7–δ ceramic to electromagnetic radiation of millimeter and optical range is studied. It is shown that the response in the optical range is not a result of interaction of radiation with the Josephson element, but is due only to the heating of the contact region by radiation. The dependence of the response on the laser power is in good agreement with the temperature dependence of the energy gap in the metal. Point contacts exhibit features characteristic of Josephson weak coupling at frequencies up to 1.5·1012 Hz. Inhomogeneities in the ceramic require a consideration of the effect of radiation on resistive elements in the current circuit, especially for large bias voltages.

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