New Superconducting Material For Levitating High-Speed Train or to Achieve Nuclear Fusion

Calendar March 13, 2023 | Posted by admin

In a historic achievement, University of Rochester researchers have created a superconducting material at both a temperature and pressure low enough for practical applications.

“With this material, the dawn of ambient superconductivity and applied technologies has arrived,” according to a team led by Ranga Dias, an assistant professor of mechanical engineering and of physics. In a paper in Nature, the researchers describe a nitrogen-doped lutetium hydride (NDLH) that exhibits superconductivity at 69 degrees Fahrenheit (26 degrees Celsius) and 10 kilobars (145,000 pounds per square inch, or psi) of pressure.

Although 145,000 psi might still seem extraordinarily high (pressure at sea level is about 15 psi), strain engineering techniques routinely used in chip manufacturing, for example, incorporate materials held together by internal chemical pressures that are even higher.

Scientists have been pursuing this breakthrough in condensed matter physics for more than a century. Superconducting materials have two key properties: electrical resistance vanishes, and the magnetic fields that are expelled pass around the superconducting material. Such materials could enable:

  • Power grids that transmit electricity without the loss of up to 200 million megawatt hours (MWh) of the energy that now occurs due to resistance in the wires
  • Frictionless, levitating high-speed trains
  • More affordable medical imaging and scanning techniques such as MRI and magnetocardiography
  • Faster, more efficient electronics for digital logic and memory device technology
  • Tokamak machines that use magnetic fields to confine plasmas to achieve fusion as a source of unlimited power

Previously, the Dias team reported creating two materials—carbonaceous sulfur hydride and yttrium superhydride—that are superconducting at 58 degrees Fahrenheit (14,4 degrees Celsius) /39 million psi and 12 degrees Fahreneheit/26 million psi respectively, in papers in Nature and Physical Review Letters.

Source: https://www.rochester.edu/

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Double Layers Of Graphene Conduct Current Without Resistance

Calendar November 14, 2018 | Posted by admin

Scientists at the Helmholtz Zentrum Berlin (HZB) have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance. They probed the bandstructure at BESSY II with extremely high resolution ARPES and could identify a flat area at a surprising location.

Carbon atoms have diverse possibilities to form bonds. Pure carbon can therefore occur in many forms, as diamond, graphite, as nanotubes, football molecules or as a honeycomb-net with hexagonal meshes, graphene. This exotic, strictly two-dimensional material conducts electricity excellently, but is not a superconductor. But perhaps this can be changed.

In April 2018, a group at MIT, USA, showed that it is possible to generate a form of superconductivity in a system of two layers of graphene under very specific conditions: To do this, the two hexagonal nets must be twisted against each other by exactly the magic angle of 1.1°. Under this condition a flat band forms in the electronic structure. The preparation of samples from two layers of graphene with such an exactly adjusted twist is complex, and not suitable for mass production. Nevertheless, the study has attracted a lot of attention among experts.

But there is one more, much simpler way of flat band formation. This was shown by a group at the HZB around Prof. Oliver Rader and Dr. Andrei Varykhalov with investigations at BESSY II. The samples were provided by Prof. Thomas Seyller, TU Chemnitz. There they are produced using a process that is also suitable for the production of larger areas and in large quantities: A silicon carbide crystal is heated until silicon atoms evaporate from the surface, leaving first a single-layer of graphene on the surface, and then a second layer of graphene. The two graphene layers are not twisted against each other, but lie exactly on top of each other.

This flat area is a prerequisite for superconductivity but only if it is situated exactly at the so-called Fermi energy. In the case of the two-layer graphene, its energy level is only 200 milli-electron volts below the Fermi energy, but it is possible to raise the energy level of the flat area to the Fermi energy either by doping with foreign atoms or by applying an external voltage, the so-called gate voltage.

The findings have been Published in Science Advances.

Source: https://www.helmholtz-berlin.de/

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