Engineering Physics

9.6 Quantum tunnelling

As shown in Fig. 9.13(a), if a thick insulating layer is sandwiched between two metals, then electric current will not pass through this insulating layer. If the insulating layer is very thin (≈ 10 to 20 Å), then there is a large probability for electrons to pass from one metal to another through this insulating layer by quantum mechanical process called tunnelling. If both the metals are normal conductors, then the V – I characteristics is a straight line as shown in Fig. 9.13(b).

In 1961, Giaever took a system in which an insulating layer of 10 nm thick has been sandwiched between a normal metal and a superconductor as shown in Fig. 9.14(a). Gradually, an increasing potential has been applied between the metal and superconductor ...