Modulated microwave absorption of a superconducting loop with two nonidentical Josephson junctions

Abstract

A regularly spaced multiline modulated-microwave-absorption (MMA) spectrum arising from two lead pieces behaving as a quantum interferometer is modeled by replacing the microwave current across two parallel Josephson junctions by a direct current I that is proportional to the square root of the microwave power P. Assuming that microwave absorption occurs only when I is greater than the field-dependent critical current Ic of the two-junction system, the peak-to-peak width δH of each MMA line is shown to depend on P according to the relation P=P0+(1-cosδα), where δα=π δH/ΔH, and ΔH is the separation of neighboring lines. The experimental data previously obtained by Drumheller, Trybula, and Stankowski were fitted to the values P0=3 mW and a=66 mW, which leads to a ratio Ia/Ib of 1.4 for the critical currents of the two junctions. A surprisingly good fit of the data to the more approximate relation P=P0+b(δH)2 is obtained for the values P0=3 mW and b=74 mW/Oe2. Predictions of the above model are compared with those of the recent theory of Vichery, Beuneu, and Lejay.

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