Superconductivity, where electricity flows through a material with absolutely no resistance, could be on the verge of changing the world if recent advances can be deployed widely. Yet our understanding of the underlying physics is still very much a work in progress. The first demonstration of a previously theorized form of superconductivity could open doors to improving that.
When cooled close enough to absolute zero some substances form a state of matter known as Bose-Einstein Condensate (BEC), or the "fifth" state of matter, where quantum mechanics replaces classical physics. BECs show the mixture of wave-like and particle-like behavior more commonly associated with photons or electrons.
"A BEC is a unique state of matter as it is not made from particles, but rather waves," said Dr Kozo Okazaki of the University of Tokyo in a statement. “As they cool down to near absolute zero, the atoms of certain materials become smeared out over space. This smearing increases until the atoms – now more like waves than particles – overlap, becoming indistinguishable from one another. The resulting matter behaves like it's one single entity with new properties the preceding solid, liquid or gas states lacked, such as superconduction,”
In Science Advances, Okazaki and colleagues have announced the first observation of superconductivity in a BEC, in this case, a compound iron and selenium.
BECs are hard enough to produce and maintain that anyone wanting superconductivity for practical purposes would opt for something more conventional. A research tool is a different matter. Most superconductors operate as Barden-Cooper-Schrieffer (BCS) regimes where atoms order themselves so as to offer electrons an uninterrupted path, something that can only happen when conditions are cold enough the atoms don’t vibrate and jostle the electrons as they pass.
"Demonstrating the superconductivity of BECs was a means to an end; we were really hoping to explore the overlap between BECs and BCSs," Okazaki said. Indeed this exactly what they achieved. Laser-based photoemission spectroscopy allowed them to observe differences in the ways electrons behave in BEC and BSC superconductivity. More importantly, they also witnessed a smooth transition from one form of superconductivity to the other.
This indicates the two regimes are different manifestations of a single underlying phenomenon, comparable to the unification of the electromagnetic and weak nuclear forces at very high energy. If a theory can be found to explain BEC and BCS superconductivity at once, it should allow us to understand BCS on a deeper level. This may allow the identification of materials that demonstrate superconductivity under a wider range of conditions.
Superconductivity under day-to-day conditions could unleash technologies out of science fiction, but we’re still a fair way off that. The recent demonstration of room temperature superconductivity required immensely high pressures, impractical for most purposes. We may need to improve our theoretical understanding if we are to produce something more widely useful, and BECs could be the path to do that.