Average kinetic energy of the superconducting state

Isothermal magnetization curves are plotted as the magnetization times the magnetic induction, 4 πM.B, versus the applied field H. We show here that this curve is the average kinetic energy of the superconducting state versus the applied field, for type-II superconductors with a high Ginzburg-Landau parameter κ. The maximum of 4πM.B occurs at a field H * , directly related to the upper critical field H c 2 , suggesting that H c 2 ( T) may be extracted from such plots even in cases when it is too high for direct measurement. We obtain these plots both theoretically, from the Ginzburg-Landau theory, and experimentally, using a Niobium sample with T c =8.5 K, and compare them.