Subharmonic frequency locking in the resistive Josephson thermometer

Phase-locked oscillatory solutions are examined as a basis for the dc impedance of the resistive superconducting quantum-interference device Josephson thermometer. The calculations are based on the resistively shunted junction model in the limit 2π$L_s$ $I_c$/${\Phi }_0$≥1, where $L_s$ is the loop inductance and $I_c$ is the junction critical current, and for a junction resistance large compared with the external shunt resistance. An algorithm for representing frequency entrainment in (κ,ω) space (drive amplitude, frequency) leads to zones with rotation number p/q having the form of leaf-shaped regions joined and overlapping at their tips. High-resonance zones are very thin and locally similar. No chaotic behavior has been observed. The model can simulate the ‘‘rising’’ curves of dc impedance as a function of drive amplitude.