Superconductivity

The Meissner effect occurs when a material transitions into a superconducting state and actively expels all internal magnetic fields from its interior. This phenomenon allows superconductors to levitate magnets above them without any physical contact.

Superconductivity was discovered by Dutch physicist Heike Kamerlingh Onnes in 1911. He observed the sudden disappearance of electrical resistance in solid mercury once it was cooled below 4.2 Kelvin using liquid helium.

Type I superconductors completely expel magnetic fields until a critical field strength is reached, at which point superconductivity is destroyed. Type II superconductors have two critical fields, allowing them to partially allow magnetic fields through via microscopic vortices while remaining mostly superconducting.

They are heavily used to create incredibly powerful electromagnets, such as those found in MRI machines and the bending magnets of particle accelerators like the Large Hadron Collider. They are also essential for quantum computing components like superconducting qubits.