Superconductivity Terms and Definitions

SymbolsTermsUnitsDefinitions
0]Hc Critical magnetic field   Magnetic field below which Type I superconductors exhibit superconductivity.
0]Hc1 Lower critical magnetic field T Magnetic field below which Type II superconductors exhibit perfect diamagnetism (exclusion of an applied magnetic field from the superconductor). Lower than Hc.
0]Hc2 Upper critical magnetic field. T Magnetic field below which Type II superconductors exhibit stable superconductivity.
B Magnetic induction T  
G Gauss   Unit of magnetic flux often used for low fields, the flux density over the earth's surface is ~ 0.5 G.
HTS High Temperature Superconductors  

Rare earth cuprate based superconductors with Tc values in excess of 30 K. First discovered by Bednorz and Müller in 1986.

Ic Critical Current A The electrical current below which a conductor exhibits superconductivity. The value is sensitive to the voltage criterion used.
Jc Critical Current Density A/m2 but A/mm² reported The electrical current density below which a conductor exhibits superconductivity. The value decreases with increasing temperature and applied field. The value is sensitive to the voltage criterion used. Commercial Nb-Ti strand can be purchased in kilometer lengths with Jc  in excess of 3000 A/mm² at 5 T.
K Kelvin   Temperature scale with zero at absolute zero and unit size the same as centigrade. 0 K = -273 ºC.
LTS Low Temperature Superconductors   All superconductors in use prior to the discovery of superconductivity in rare earth cuprates in 1986. The highest Tc in this class is for Nb3Ge (23 K at 0 T)
T Tesla   Unit preferred for high fields. 1 T = 10 kG
Tc Critical Temperature K The temperature below which a material exhibits superconductivity. Typically given for zero current and applied field. The value decreases with increasing current and applied field.
Type I Type I superconductors   Most elemental superconductors are of this type. They exhibit perfect diamagnetism.
Type II Type II superconductors   Alloy and HTS superconductors as well as Nb, V and Tc. Retain superconductivity beyond initial flux penetration at Hc1 up to a much higher upper critical field, Hc2
k Ginzburg-Landau parameter, "kappa" None l/x
l(T) Magnetic penetration depth Nm Depth to which an external field penetrates a superconductor. As low as 30 nm for Nb and as high as 1000 nm for YBa2Cu3O7 with field parallel to the a-b plane. Temperature (T) sensitive.
x(T) Coherence Length Nm The minimum distance over which the density of superconducting electrons may change significantly. Temperature (T) sensitive. Ranges from ~2 nm for YBa2Cu3O7 (with field parallel to the a-b plane) to 83 nm for Pb.
F Magnetic flux Wb weber
t Reduced temperature   T/Tc

Created April 18 2002 ©Peter J. Lee

Last modified on 17 November 2015