Theory of the voltage-current characteristics of high Tc asymmetric DC SQUIDs

The theory developed previously for symmetric high T-c DC SQUID is extended to account for different critical currents I-C1, I-C2 and normal resistances R-1, R-2 of Josephson junctions. The theory is based on analytical solution of a two-dimensional Fokker-Planck equation, which describes the dynamical behavior of DC SQUID in presence of thermal noise. The theory is valid for large inductance (L > 100 pH) high T-c asymmetric DC SQUIDs with any values of critical currents of Josephson junctions and asymmetry parameters. The analytical expressions for the voltage modulation and for the shift of the voltage-flux curve under bias reversal are obtained. It is shown that the sensitivity of the voltage modulation to asymmetry of DC SQUID is strongly dependent on the level of thermal noise. The expression for the shift of voltage-flux curve can be used for the determination of the parameters of asymmetry from experimental dependencies. (C) 2002 Elsevier Science B.V. All rights reserved.