Meissner Effect
The active expulsion of magnetic flux from the interior of a superconductor as it cools below its critical temperature T_c.
Governing formula
B_internal = 0, M = -H (Perfect Diamagnetism)
SI unit
T (Magnetic Flux Density B)
In depth
The Meissner effect proves that a superconductor is a perfect diamagnet rather than merely a zero-resistance conductor. Persistent surface screening supercurrents spontaneously generate opposing magnetic fields that cancel internal flux completely.
Examples in the real world
A high-temperature YBCO superconducting ceramic disk levitating stably above a neodymium magnet track.