Simplified model for current-voltage characteristics of a superconductor normal metal-superconductor junctions

We calculate an analytical approximate density of Andreev states which is used to simplify substantially the microscopic current-voltage expression of the Kummel-Nicolsky theory for superconductor-norma metal-superconductor junctions. The current expression obtained is easy to be numerically integrated and the resulting CVC exhibits all essential features of the original one and the same shape. That simplified expression for the current may fit experimental curves using only junction parameters with relevant physical meaning. In this way it may substitute the known RSJ model, which is just an equivalent circuit without a physical content.