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Gizmorama - Scientists aim to make superconductors that work at room temperature
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Gizmorama - October 5, 2016
If superconductors could operate at room temperature just think of the overall decrease in energy use and cost. It would be staggering, right?
Learn about this and more interesting stories from the scientific community in today's issue.
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*-- Scientists aim to make superconductors that work at room temperature --*
UPTON, N.Y. - Superconductors, which allow resistance-free electric flows, are greatly superior to semiconductors. Unfortunately, they only work at extremely low temperatures -- within a few degrees of absolute zero.
Researchers at the Department of Energy's Brookhaven National Laboratory are trying to design superconductors that work at room temperature. Recently, they had a breakthrough.
Cuprate superconductors are superconductors that work at relatively high temperatures -- relatively being the key word. To date, the highest temperature at which a cuprate superconductor has carried electricity while avoiding "roadblocks" -- without losing any energy to heat -- is minus 70 degrees Celsius.
Scientists first created high-temperature superconductors by incorporating the element strontium into cuprate materials -- combinations of iron and oxygen. Together with cold temperatures, strontium causes the superconductor's electrons to pair up and move friction-free. Normally, electrons repel each other.
Until now, researchers haven't exactly understood why cuprate superconductors work. What determines the temperature at which the material assumes its superconducting abilities? Why minus 70 degrees and not minus 10?
Previously, scientists have hypothesized that the transition temperature in cuprate superconductors is dictated by the strength of the electron-pairing interaction. But new research suggests it is actually determined by the density of electron pairs.
Scientists measured the density of electron pairs in a variety of cuprate samples, with varying amounts of added strontium, by sending a magnetic field force through the superconductor. The distance the magnetic field is able to travel is directly related the density of electron pairs.
Researchers found the presence of strontium makes cuprates more conductive, but the larger the concentration of strontium, the fewer electron pairs -- the fewer electron pairs, the lower the transition temperature drops toward absolute zero.
While the new research reveals, for the first time, a strong correlation between strontium and electron coupling, researchers still don't understand why electrons do or don't pair up. If they can solve that mystery, researchers say they will be closer to building superconductors with real world applications.
"These materials wouldn't require any cooling, so they'd be relatively easy and inexpensive to incorporate into our everyday lives," BNL science writer Ariana Tantillo wrote in an update. "Picture power grids that never lose energy, more affordable mag-lev train systems, cheaper medical imaging machines like MRI scanners, and smaller yet powerful supercomputers."
*-- New oscillating material may tap unused electromagnetic spectrum --*
PALO ALTO, Calif. - The terahertz gap is an unused portion of the electromagnetic spectrum comprising frequencies between radio waves and infrared radiation. No technologies currently utilize terahertz signals.
But that could soon change thanks to scientists at Stanford University, who recently developed a material that allows electrons to oscillate at terahertz frequencies.
Stanford professor and Nobel laureate Felix Bloch first theorized that uniquely structured materials could host terahertz oscillations several decades ago. Now, scientists believe they've turned theory into reality.
The key to hosting Bloch's oscillations is creating consistent nanoscale patterns so electrons can travel without interruption for significant distances. The ideal medium for such patterns are two-dimensional materials and superlattices, like graphene.
Graphene consists of atom-thick layers of carbon. The carbon atoms are arranged in a lattice or honeycomb-like pattern. Researchers found that when they sandwiched a sheet of graphene between two layers of boron nitride, electrons flow along a special wave interference pattern called a moiré pattern -- a pattern Bloch theorized could host terahertz signals.
If researchers can trap electrons within the narrow energy bands of the moiré superlattice for long enough, they should vibrate at terahertz frequencies. Now that they have a proper medium, researchers say they are a step closer to emitting and sensing of terahertz signals.
The moiré superlattice material also presented a surprising new electronic structure.
"In semiconductors, like silicon, we can tune how many electrons are packed into this material," David Goldhaber-Gordon, a physics professor at Stanford, said in a news release. "If we put in extra, they behave as though they are negatively charged. If we take some out, the current that moves through the system behaves as if it's instead composed of positive charges, even though we know it's all electrons."
In the new material, the opposite is true. Additional electrons produce a positive charge, while subtraction yields a negative charge.
Researchers say the new materials could ultimately inspire a variety of new technologies. Ultra-sensitive terahertz scanners could replace microwaves scanners at airport security checkpoints, for example.
"This is going to be an area that opens up a lot of new possibilities," said Goldhaber-Gordon, "and we're just at the start of exploring what we can do."
Researchers described their latest findings in the journal Science.
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