My favourite theory (other than the mundane and vastly more likely stuff) is some lab during WWII produced some extremely high field room temperature supercondu

My favourite theory (other than the mundane and vastly more likely stuff) is some lab during WWII produced some extremely high field room temperature superconductor. The US got hold of it afterward and made a bunch of toys, but noone knows how to manifacture more and most of it has been destroyed now.