The London penetration depth, also known as the London depth or the London length, is a measure of how far a magnetic field can penetrate into a superconductor. It is named after the British physicist Fritz London.
The Josephson penetration depth is a measure of the distance over which an electromagnetic wave can penetrate into a Josephson junction, which is a device made up of two superconductors separated by a thin insulating layer. It is named after the British physicist Brian David Josephson.
The main difference between London and Josephson penetration depths is the type of superconductor they apply to. The London penetration depth is used for conventional superconductors, while the Josephson penetration depth is used for Josephson junctions and high-temperature superconductors.
Both London and Josephson penetration depths can be measured using various experimental techniques, such as microwave resonator measurements, tunneling spectroscopy, and magnetic field-dependent critical current measurements.
The London and Josephson penetration depths are affected by several factors, including temperature, magnetic field strength, and material properties of the superconductor. In addition, the London penetration depth is also influenced by impurities and defects in the material.