Ratchet potential in d.c. SQUID’s and reduced two-junction interferometer models

For finite values of the parameter β and in the presence of small structural asymmetry and inhomogeneity of the junctions parameters, the two-junction interferometer model can be described by means of a single non-linear differential equation in such a way that a ratchet potential for SQUID’s can be deduced. The resulting dynamical equation, derived for first-order corrections with respect to a symmetric and homogeneous model with β=0, presents an additional second-harmonic term and a cosine term in the expression for the effective current-phase relation. For opportune values of the perturbation parameters a ratchet potential with pre-definite characteristics can be obtained. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005