A neodymium magnet cube sits on a surface of yttrium barium copper oxide—YBa2Cu3O7, nicknamed YBCO—inside the bottom of a styrofoam cup. A small amount of liquid nitrogen is poured slowly over the YBCO. As it cools, the disc becomes a superconductor… and the cube levitates. Behold the Meissner Effect, as demonstrated in this video from the Harvard Natural Sciences Lecture Demonstrations YouTube channel.
What causes the cube to hover as if by magic? From Scientific American:
Quantum magnetic levitation boils down to something called the Meissner effect, which only occurs when a material is cold enough to behave like a superconductor. At normal temperatures, magnetic fields can pass through the material normally. Once it is cold enough to exhibit superconductivity, however, those magnetic fields get expelled. Any magnetic fields that were passing through must instead move around it. When a magnet is placed above a superconductor at critical temperature, the superconductor pushes away its field by acting like a magnet with the same pole causing the magnet to repel, that is, “float”—no magical sleight of hand required.
Read more about Harvard’s DIY demo and Dartmouth’s safety precautions for handling liquid nitrogen.
Then watch more demonstration videos, more videos about magnetic fields and more levitation videos, including this spooky holiday version: Levitating pumpkins! Halloween superconductor science.