Voltage-flux-characteristics of asymmetric dc SQUIDs

We present a detailed analysis of voltage-flux V(phi)-characteristics for asymmetric dc SQUIDs with various kinds of asymmetries. For finite asymmetry or in the critical currents of the two Josephson junctions, the minima in the V(phi)-characteristics for bias currents of opposite polarity are shifted along the flux axis by Delta phi = alpha (1)beta (L), relative to each other; pr. is the screening parameter. This simple relation allows the determination of or in our experiments on YBa2Cu3O7-delta dc SQUIDs and comparison with theory. Extensive numerical simulations within a wide range of pr and noise parameter Gamma reveal a systematic dependence of the transfer function V-phi on alpha (1) and alpha (R) (junction resistance asymmetry). As for the symmetric de SQUID, V phi factorizes into g(Gamma beta (L)) f(alpha (1),beta (L)), where now f also depends on alpha (1). For beta (L)less than or similar to5 we find mostly a decrease of V-phi with increasing alpha (1), which however can only partially account for the frequently observed discrepancy in V-phi between theory and experiment for high-Tc dc SQUIDs.