London, February 13 : Physicists at the Massachusetts Institute of Technology (MIT) have made a significant advance in understanding the puzzling nature of high-temperature superconducting materials that conduct electricity without any resistance at temperatures well above absolute zero.
The research team claims that its discovery may overturn theories about the state of matter in which superconducting materials exist just before they start to superconduct.
Eric Hudson, MIT assistant professor of physics, says that understanding high-temperature superconductors is one of the biggest challenges in physics today.
In a study report, he says that most superconductors only superconduct at temperatures near absolute zero. However, about two decades ago, it was found that some ceramics can superconduct at higher temperatures, he adds.
The report further states that, though such high-temperature superconductors are being used for many applications like cell-phone base stations and a demo magnetic-levitation train, their potential applications could be much broader.
"If you could make superconductors work at room temperature, then the applications are endless," Nature Physics quoted Hudson as saying.
Superconductors are superior to ordinary metal conductors such as copper because current does not lose energy as wasteful heat as it flows through them, thus allowing larger current densities. Once a current is set in motion in a closed loop of superconducting material, it will flow forever.
The researchers looked at a state of matter that superconductors inhabit just above the temperature at which they start to superconduct.
During the superconducting state, all electrons in a material are at the same energy level. The range of surrounding, unavailable electron energy levels is called the superconducting gap.
It is considered to be a critical component of superconduction because it prevents electrons from scattering, and thereby eliminates resistance and allows the unimpeded flow of current.
Just above the transition temperature when a material starts to superconduct, it exists in a state called the pseudogap. This state of matter is not at all well understood, say the researchers.
Hudson's team decided to investigate the nature of the pseudogap state by studying the properties of electron states that were believed to be defined by the characteristics of superconductors: the states surrounding impurities in the material.
It had already been shown that natural impurities in a superconducting material, such as a missing or replaced atom, allow electrons to reach energy levels that are normally within the superconducting gap, so they can scatter.
Using a new method called scanning tunnelling microscopy (STM), the researchers have shown that scattering by impurities occurs when a material is in the pseudogap state as well as the superconducting state.
They say that this finding challenges the theory that the pseudogap is only a precursor state to the superconductive state, and offers evidence that the two states may coexist.
Hudson believes that the method of comparing the pseudogap and superconducting state with the help of STM may enable physicists to understand why certain materials are able to superconduct at such relatively high temperatures.
"Trying to understand what the pseudogap state is a major outstanding question," he said.