Quantum Superconducting Effects

Although many properties of superconductors can be described in macroscopic terms such as resistivity, heat capacity, critical temperature, etc., superconductivity is at base a quantum phenomenon and several interesting quantum effects arise.

In 1961, two groups working independently discovered flux quantization - the fact that the magnetic flux through a superconducting ring is an integer multiple of a flux quantum.

The Cooper pairs of a superconductor can tunnel through a thin insulating layer between two superconductors. This is the basis for the Josephson junction which is used in high-speed switching devices.

Index

Superconductivity concepts

Reference Rohlf,Ch 15
 
HyperPhysics***** Condensed Matter R Nave
 Go Back





Flux Quantization

Deaver and Fairbank did experiments with a tiny superconducting cylinder made by electroplating tin on a copper wire. They found magnetic flux quantized in units of

Φ0 = 2 x 10-15 Tm2

such that the flux through the cylinder was given by

Φm = nΦ0

More precise measurements using a SQUID magnetometer give a value for the flux quantum:

This can be seen to be determined by Planck's constant and the electron charge, so it is tied to fundamental physical constants. 		Index

Superconductivity concepts

Reference Rohlf
 
HyperPhysics***** Condensed Matter R Nave
 Go Back