1. Introduction

In 1962, Brian Josephson proposed a novel behavior of superconductor called Josephson junction. Josephson junction is a junction of two superconducting material separated by a thin insulating layer. This sandwich starts conducting when cooper fig1.1 pairs from both the metal layers tunnel through insulators. Here cooper pairs means pair of electrons at T<T_c. The wave function of this pair is exactly like the wave function of free particle having opposite spin and equal and opposite momentum [2]. This pair condensation named after American physicist Leen Cooper is one of the basis for development of BCS theory of superconductivity[1].

These electron pairs behaves like bosons and responsible for the flow of electrons through the insulating layer with phase difference ∆φ. There exist two types, one is DC (in the absence of electric and magnetic field) and another one is AC (applied DC across the junction) Josephson Effect depending upon the type of current that flows between the junctions When a DC voltage is applied across a Josephson junction it produces a current with oscillating frequency

 

Thus we can calculate with very high accuracy because voltage and frequency can be determined precisely [1].