Superconductors are materials that conduct electricity with no resistance and expel magnetic fields when cooled to ultralow temperatures. And depending on their quantum structure, they can also showcase strange properties like magnetic levitation. But now things are getting a little weirder.

One of the most fascinating phenomena related to superconductors is the breaking of time-reversal symmetry. TRS is the principle that a physical system behaves the same way whether time runs forward or backward. Rare unconventional superconductors break this symmetry. When this happens, they spontaneously generate tiny internal magnetic fields when they enter their superconducting state.

Until recently, every superconductor known to do this was a type II material. But in a study published in the journal Physical Review Letters, researchers report the discovery of a type I superconductor that breaks time-reversal symmetry too.