Electrons in Iron-based Superconductors Can Pair Up in Two Different Ways
August 3, 2018 | RIKENEstimated reading time: 2 minutes
By mapping uneven patterns of electrons in iron-based superconductors, RIKEN researchers have found evidence that electrons can pair up in two different ways, depending on the crystal structure (Science Advances, "Two distinct superconducting pairing states divided by the nematic end point in FeSe1-xSx"). This finding could help scientists in their quest to design materials that superconduct at relatively mild temperatures.
Figure 1: By mapping electron patterns in crystals of iron selenide containing increasing amounts of sulfur, RIKEN researchers have found evidence that electrons in the superconductor pair up in two different ways. (Image: From Ref. 1. T. Hanaguri et al., some rights reserved; exclusive licensee American Association for the Advancement of Science. Distributed under a CC BY-NC 4.0 license)
Superconductors carry electrical current with no resistance and are used to create powerful electromagnets and sensitive magnetic detectors. However, most superconduct only at extremely low temperatures, limiting their practical application. So physicists are investigating high-temperature superconductors that operate well above -196 degrees Celsius, the temperature of liquid nitrogen.
Superconductivity occurs when electrons pair up, which slightly lowers their energy and creates an energy gap that stops them scattering as they flow through the material. In some copper- or iron-based superconductors, this pairing is closely related to a distortion in the material’s structure known as the nematic phase. As a result, certain electrons around the metal atoms can adopt different energy states, giving them a more uneven distribution than in the non-nematic phase.
Tetsuo Hanaguri of the RIKEN Center for Emergent Matter Science and colleagues have now probed the relationship between nematicity and superconductivity in a family of materials based on iron selenide.
Iron selenide enters its nematic phase below about -183 degrees Celsius. Swapping some of the material’s selenium atoms for sulfur ones weakens this nematicity, and once the ratio of sulfur atoms to selenium ones exceeds about one fifth (known as the nematic end point), the temperature at which the transition to the nematic phase occurs begins to fall.
The researchers studied crystals of iron selenide sulfide with varying sulfur content using a technique called spectroscopic imaging scanning tunneling microscopy. This allowed them to measure the precise chemical compositions of the samples as well as key electronic properties of the material (Fig. 1).
As the sulfur content increased up to the nematic end point, the energy gap of superconducting electron pairs did not change. However, the energy gap suddenly shrank beyond the nematic end point. This suggests that the superconducting electrons could pair up in two different ways, depending on the material’s nematicity.
“Our data clearly indicate that there is an intimate relationship between nematicity and superconductivity,” says Hanaguri. “This is an important constraint for the theory of iron-based superconductivity, because the correct theory must account for this characteristic behavior.”
The researchers now plan a more detailed investigation of the superconducting energy gaps in the nematic and non-nematic phases of iron selenide sulfides, and they aim to study other superconducting materials in the same way.
“This may lead to the design of as-yet-unknown exotic, and hopefully high-temperature, superconductors,” notes Hanaguri.
Suggested Items
The Chemical Connection: Reducing Etch System Water Usage, Part 2
05/02/2024 | Don Ball -- Column: The Chemical ConnectionIn my last column, I reviewed some relatively simple ways to reduce water usage in existing etch systems: cutting down cooling coil water flow, adding chillers to replace plant water for cooling, lowering flow rate nozzles for rinses, etc. This month, I’ll continue with more ways to control water usage in your etcher. Most of these are not easily retrofittable to existing equipment but should be given serious consideration when new equipment is contemplated. With the right combination of add-ons, it is possible to bring the amount of water used in an etch system to almost zero.
Designer’s Notebook: What Designers Need to Know About Manufacturing, Part 2
04/24/2024 | Vern Solberg -- Column: Designer's NotebookThe printed circuit board (PCB) is the primary base element for providing the interconnect platform for mounting and electrically joining electronic components. When assessing PCB design complexity, first consider the component area and board area ratio. If the surface area for the component interface is restricted, it may justify adopting multilayer or multilayer sequential buildup (SBU) PCB fabrication to enable a more efficient sub-surface circuit interconnect.
Insulectro’s 'Storekeepers' Extend Their Welcome to Technology Village at IPC APEX EXPO
04/03/2024 | InsulectroInsulectro, the largest distributor of materials for use in the manufacture of PCBs and printed electronics, welcomes attendees to its TECHNOLOGY VILLAGE during this year’s IPC APEX EXPO at the Anaheim Convention Center, April 9-11, 2024.
ENNOVI Introduces a New Flexible Circuit Production Process for Low Voltage Connectivity in EV Battery Cell Contacting Systems
04/03/2024 | PRNewswireENNOVI, a mobility electrification solutions partner, introduces a more advanced and sustainable way of producing flexible circuits for low voltage signals in electric vehicle (EV) battery cell contacting systems.
Heavy Copper PCBs: Bridging the Gap Between Design and Fabrication, Part 1
04/01/2024 | Yash Sutariya, Saturn Electronics ServicesThey call me Sparky. This is due to my talent for getting shocked by a variety of voltages and because I cannot seem to keep my hands out of power control cabinets. While I do not have the time to throw the knife switch to the off position, that doesn’t stop me from sticking screwdrivers into the fuse boxes. In all honesty, I’m lucky to be alive. Fortunately, I also have a talent for building high-voltage heavy copper circuit boards. Since this is where I spend most of my time, I can guide you through some potential design for manufacturability (DFM) hazards you may encounter with heavy copper design.