It has been 25 years since scientists discovered the first high-temperature superconductors—copper oxides, or cuprates, that conduct electricity without a shred of resistance at temperatures much higher than other superconducting metals. Yet no one has managed to explain why these cuprates are able to superconduct at all. Now, two Caltech chemists have developed a hypothesis to explain the strange behavior of these materials, while also pointing the way to a method for making even higher-temperature superconductors.
Superconductors are invaluable for applications such as MRI machines because they conduct electricity perfectly, without losing any energy to heat—a necessary capability for creating large magnetic fields. The problem is that most superconductors can only function at extremely low temperatures, making them impractical for most applications because of the expense involved in cooling them.
A value known as the maximum Tc indicates the highest temperature at which a material can superconduct. The superconductor used in MRI—the metal alloy niobium tin—has a maximum Tc of -248˚C. Cooling this material to such a frigid temperature requires liquid helium, a scarce and extremely expensive commodity.