The current phase relation in Josephson tunnel junctions

The J(Phi) relation in SFIFS, SNINS, and SIS tunnel junctions is studied. A method for the analytical solution of linearized Usadel equations has been developed and applied to these structures. It is shown that the Josephson current across the structure has a sum of sin Phi and sin 2 Phi components. Two different physical mechanisms are responsible for the sign of sin 2 Phi. The first one is the depairing by current, which contributes positively to the sin 2 Phi term, while the second one is the finite transparency of SF or SN interfaces, which provides the negative contribution. In SFIFS junctions, where the first harmonic vanishes at the 0-pi transition, the calculated second harmonic fully determines the J(Phi) curve. (C) 2005 Pleiades Publishing, Inc.