Superconductivity is not very low resistance but exactly zero, and it does not ease down with temperature: it plunges vertically right at Tc. A YBCO ceramic sample has a Tc near 92 K, so cooling it from room temperature down to liquid nitrogen at 77 K is enough, with no need for the liquid helium required when mercury first superconducted at 4.2 K in 1911. Below Tc the Meissner effect expels the magnetic field entirely and the magnet floats; a type-II material, though, lets a few flux tubes through and pins them in place, which is why a sample stays put even when tilted or hung upside down.
Superconductivity is not very low resistance but exactly zero, and it does not ease down with temperature: it plunges vertically right at Tc. A YBCO ceramic sample has a Tc near 92 K, so cooling it from room temperature down to liquid nitrogen at 77 K is enough, with no need for the liquid helium required when mercury first superconducted at 4.2 K in 1911. Below Tc the Meissner effect expels the magnetic field entirely and the magnet floats; a type-II material, though, lets a few flux tubes through and pins them in place, which is why a sample stays put even when tilted or hung upside down.
Related topics in Matter & Atom