Things Start Warming Up
So far, this has all been a standard description of superconductors—the kind of stuff that had Kamerlingh Onnes scratching his head back in 1911. But the term “superconductor” is really an umbrella term for a variety of materials that can achieve superconductivity in a variety of ways.
Some materials—known as s-wave, d-wave, p-wave, and recently g-wave superconductors—are categorized by how two electrons specifically pair up in the first place. Other superconductors use entirely different mechanisms that don’t require phonons at all, or react to magnetic fields in different ways (Type I and Type II superconductors), and some even reach Tc at temperatures scientists once thought impossible.
“Based on the [BCS] theory, it was thought that nothing could superconduct above 40 Kelvin,” Greene says. “That idea was completely destroyed in the 1980s when a new material was discovered: copper oxides.”