Note 1 to entry: $\xi$ , defined in the Ginzburg-Landau theory, is a function of temperature and nearly equal to the BCS coherence length, ${\xi }_0$ , at 0 K in a clean superconductor.

Note 2 to entry: $\xi ={\left({\Phi }_0/2\pi {\mu }_0{H}_{\mathrm{c}2}\right)}^{1/2}$ , where ${\Phi }_0$ is the flux quantum, ${\mu }_0$ is the magnetic constant and $H_{\mathrm{c}2}$ is the upper critical field strength.

Note 3 to entry: This entry was numbered 815-10-32 in IEC 60050-815:2015.