a Coupled Angular Momentum Model for the Josephson Junction.

A model for the Josephson junction is constructed based on two macroscopic angular momentum vectors. These vectors, which interact via a Heisenberg-like Hamiltonian, are defined using Anderson's pseudospin concept in superconductivity. Along with this, a new state vector, which affords a more complete description of the constant-charge-imbalance mode of the junction, is explicitly constructed. The resulting equations of motion lead directly to the basic Josephson results and at the same time provide a simple physical picture for the dynamical behavior of the junction. Both the Anderson (n,(phi)) and Feynman two-state models of the junction are shown to be equivalent to a restricted form of the angular momentum approach. The process of formulating the junction problem in terms of pseudo-angular-momentum together with the above identification constitutes a microscopic derivation of the Feynman method. A perturbation theory calculation is carried out within the full pseudo-angular -momentum equations of motion to determine how this approach differs from the earlier ones.