Figure 166: Schematic illustration of the IV characteristic of a tunnel barrier device, i.e. two metals
separated by a thin insulator.
Figure 167: Schematic illustration of the IV characteristic of a superconducting tunnel barrier device,
i.e. two metals separated by a thin insulator, where one of the metals is superconducting.
16.4.6 TheJosephsonEffect
16.4.5 Single Particle Tunneling
We regard the situation of two metals separated by a thin insulating layer. In the classical case, one
observes tunneling through the barrier when a voltage is applied. The typical IV characteristic is of
the form illustrated in Fig. 166, i.e. the current rises linearly with the applied voltage. The situation
changes drastically if one of the metal plates is a superconductor, Fig. 167. This is due to the bandgap
occurring in superconductors, Fig. 162. AtT = 0K, no current can flow until the applied voltage
exceedsV =E 2 qg. At finite temperatures one observes a small current also at low temperatures due to
thermal excitations of electron pairs across the bandgap.