hc/4e oscillations in a model for (100)/(110) SQUIDs of d-wave superconductors

We use a model of hard-core bosons to describe a SQUID built with two crystals of $d_{x^2-y^2}$-superconductors with orientations (100) and (110). Across the two faceted (100)/(110) interfaces, the structure of the superconducting order parameter leads to an alternating sign of the local Josephson coupling, and the possibility of quartet formation. Using a mapping of the boson model to an $XXZ$ model, we calculate numerically the energy of the system as a function of the applied magnetic flux, finding signals of $hc/4e$ oscillations in a certain region of parameters. This region has a large overlap to that at which binding of bosons exists.