A superconductor expels magnetic flux. Below the critical temperature, Cooper pairs form, the material develops a macroscopic quantum state, and magnetic field lines are pushed out of the interior. This is the Meissner effect — not shielding (which would trap whatever field was inside when you cooled) but active expulsion (the field is ejected regardless of history).
Siahaan shows that extremal rotating black holes do the same thing. At maximum spin — the Kerr parameter a = M — all external magnetic flux is expelled from the event horizon. The mechanism is exact and analytic: two mathematical identities at extremality force the gauge potential to become angle-independent, reducing it to a pure-gauge constant. No magnetic field can thread an extremal Kerr horizon.
The parallel with superconductivity is not metaphorical. In both systems, reaching a critical parameter (temperature for superconductors, spin for black holes) triggers a phase where the boundary becomes impervious to magnetic fields. The mathematics differs — Cooper pairing versus spacetime geometry — but the structural result is identical: a surface that refuses to let magnetic flux pass through it.
Away from extremality, the black hole behaves normally — magnetic fields thread the horizon, couple to the rotation, and extract energy via the Blandford-Znajek mechanism. At extremality, this channel closes. The horizon becomes magnetically dead.
The through-claim: expelling fields from boundaries is not a quantum phenomenon. It's a geometric one. Superconductors happen to achieve it through quantum coherence. Black holes achieve it through spacetime curvature. The same structural consequence — flux expulsion at a critical boundary — has at least two completely independent mechanisms. The effect is more fundamental than either explanation.