Josephson effect

This effect was first predicted by Josephson in 1962. The experimentalarrangement was a Josephson junction which consists of a thininsulator sandwiched between two superconductors as shown:If the insulator layer is very thin, of the order of 10-50 Å inthickness, a tunneling phenomenon called Josephson tunneling(Josephson effect) takesplace through the insulator. Thus theinsulator turns into a superconductor.With no applied voltage, a dc current (ic) will flow across thejunction. This is called dc Josephson effect. When a small voltage isapplied across the junction, current oscillates with a frequency This is called ac Josephson effect. If the applied voltage isincreased beyond the critical voltage (vc), the current attains anohmic behaviour.If a magnetic field is applied perpendicular to the junction, thevalue of critical supercurrent drops to zero whenever flux through thejunction is a multiple of flux quantum 0. This property is used inSQUID (Superconducting QUantum Interference Device).