Following the dream of realizing a high-temperature superconductor, Cornell University researchers just found something about iron-based materials: they can be made to resemble electronic liquid crystals.
“Because these findings appear similar to what we have observed in the parent state of [copper-based] superconductors, it suggests this could represent a common factor in the mechanism for high-temperature superconductivity in these two otherwise very different families of materials,” said team leader J.C. Séamus Davis, Cornell’s J.D. White Distinguished Professor of Physical Sciences and director of the U.S. Department of Energy’s Center for Emergent Superconductivity. The researchers describe their findings in the Jan. 8 issue of the journal Science.
Until now, in theory, scientists expected that the iron-based materials should behave like conventional metal superconductors, where electrons carry the current without needing any special arrangement of the atoms in the metal. The disadvantage of using such metals is that they need to be cooled to -270 degrees Celsius to work.
Doping the iron-based materials with arsenic changes the crystalline structure of the material in a manner that lets electrons flow without resistance. So, if you would want to make this material superconduct, it would be much easier in terms of temperatures and energy, since the atoms flow more easily.
By using a specially designed scanning tunneling microscope (STM), scientists moved a tiny probe across a surface in steps smaller than the width of an atom. By modifying the current flowing between the probe and the surface, J.C. Séamus Davis, Cornell’s J.D. White Distinguished Professor of Physical Sciences, read out a spectrum of the electrons’ energy levels in the material. They even took a picture with the distribution of electrons.
It became clear to the team that they were on to something very different than expected. They observed static, nanoscale lineups of electrons spanning about eight times the distance between individual iron atoms, all aligned along one axis of the underlying crystal, reminiscent of the way molecules line up in a liquid crystal.
Liquid crystals, used in electronic displays, are a sort of intermediate state between liquid and solid in which molecules line up in parallel rows that can control the passage of light. In the solid crystals of materials like high-temperature superconductors, electrons do not remain attached to individual atoms but behave like a fluid, and here, Davis said, the electrons seem to be in a state analogous to a liquid crystal. “You can’t use ordinary solid-state physics to understand materials this complicated,” he said.
High-temperature superconductors are a must for the future’s energy needs. Current regular conductors probably won’t be enough to transport the electricity generated and moved across the supergrids that the United States and Europe plan to build.