In 1911, a Dutch scientist discovered a class of materials named Superconductors which, at temperatures near absolute zero, could conduct electricity with no resistance and therefore zero loss of power. Conventional superconductors consist of simple metals, such as niobium, lead, or mercury, which become superconducting when cooled to below a characteristic “critical temperature” close to absolute zero—4.2 K in the case of mercury. These became known as Low Temperature Superconductor (LTS) materials.
Superconductivity gives materials two key properties. Electrical resistance vanishes. And any semblance of a magnetic field is expelled, due to a phenomenon called the Meissner effect. The magnetic field lines have to pass around the superconducting material, making it possible to levitate such materials, something that could be used for frictionless high-speed trains, known as maglev trains. Powerful superconducting electromagnets are already critical components of maglev trains, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) machines, particle accelerators and other advanced technologies, including early quantum supercomputers.
Since the 1960s a Niobium-Titanium (Ni-Ti) alloy has been the material of choice for commercial superconducting magnets. More recently, a brittle Niobium-Tin intermetallic material has emerged as an excellent alternative to achieve even higher magnetic field strength. These Conventional superconductors like niobium-tin and niobium-titanium operate only at temperatures so low that you need expensive (and non-renewable) liquid helium. to create them. That puts a limit on how much you can do with these “low-temperature” superconductors.
Current superconductors work when cooled near absolute zero, and the warmest superconductor, hydrogen sulfide, works at -95 degrees Fahrenheit, extremely low temperatures—lower than any natural temperatures on Earth. This restriction makes them costly to maintain—and too costly to extend to other potential applications. “The cost to keep these materials at cryogenic temperatures is so high you can’t really get the full benefit of them,” Dias says. Others have claimed to have invented a room-temperature superconductor in the past.
Applications of semiconductors include 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; A new way to propel levitated trains and other forms of transportation; Medical imaging and scanning techniques such as MRI and magnetocardiography and Faster, more efficient electronics for digital logic and memory device technology
If scientists can develop them to function at room temperature, they may one day replace anything requiring electricity—including entire power grids. A room-temperature superconductor or HTS is a material that is capable of exhibiting superconductivity at temperatures around 77 degrees Fahrenheit. In 1986, J. G. Bednorz and K. A. Müller discovered oxide based ceramic materials that demonstrated superconducting properties as high as 35K. This was quickly followed in early 1997 by the announcement by C. W. Chu of a cuprate superconductor functioning above 77K, the boiling point of liquid nitrogen.
Since then, extensive research worldwide has uncovered many more oxide based superconductors with potential manufacturability benefits and critical temperatures as high as 135K. A superconducting material with a critical temperature above 23.2K is known as a High Temperature Superconductor (HTS), despite the continuing need for cryogenic refrigeration for any application. Scientists continue to hunt for new materials that superconduct under various conditions (in addition to lowering the thermostat, increasing pressure can change a material into a superconducting state).
In 2019, Two Indian scientists claimed to have made a room-temperature superconductor using particles of gold and silver. Other physicists are using pressurized lanthanum and hydrogen. One HTS application is already a reality: stronger research magnets, which scientists use to study materials, disease, complex molecules like oil and proteins, among many other areas.
High Temperature Superconductor (HTS)
These materials called Superconductors have unique properties including, Zero resistance to direct current; Extremely high current carrying density; Extremely low resistance at high frequencies; Extremely low signal dispersion; High sensitivity to magnetic field; Exclusion of externally applied magnetic field; Rapid single flux quantum transfer; and Close to speed of light signal transmission.
Magnesium diboride (MgB2) was discovered to be a high Tc superconductor in 2001. It actually falls somewhere between a low-temperature and high-temperature superconductor. It appears to work, at least in part, like a low-temperature superconductor: via a phenomenon known as Cooper pairs. Scientists at CERN have demonstrated that, when cold, it’s an outstanding conductor, findings that suggest it could be used in long-distance power transportation. “MgB2 is cheap, abundant and lightweight,” said engineering professor Eric Hellstrom, who studies high Tc superconductors at the ASC. “For that combination of properties, there may be a special niche of potential applications.”
New superconducting compounds, however, can operate at much higher temperatures than conventional superconductors. Researchers have also explored copper oxides and iron-based chemicals as potential candidates for high temperature superconductors in recent years. First came BSCCO, shorthand for bismuth strontium calcium copper oxide — or “bisco” (rhymes with Crisco). Within a few years of the Bednorz/Muller discovery, engineers were making wire of it, which is now used in some very high-tech transmission cable, transformers, motors and generators and magnets.
There are different types of BSCCO, depending on its exact chemical composition, including Bi-2223 and Bi-2212. The MagLab is using the latter to build a novel research magnet dubbed the Platypus, a high-field (24-tesla) instrument for nuclear magnetic resonance research. Elsewhere, scientists are working with Bi-2223 to build current leads for research magnets. Both of these forms of BSCCO superconduct well above liquid nitrogen temperatures. Of all classes of high-temperature superconductors, cuprates continue to boast the highest transition temperature — the point below which they are superconducting. A cousin of BSCCO is ReBCO, another cuprate. In this high-Tc superconductor, the barium, copper and oxygen found in BSCCO is joined by one of the rare earth elements (hence the “Re”).
One variation is YBCO, the Y standing for the rare earth element yttrium. In collaboration with industry partners, MagLab scientists and engineers have done extensive research and development on ReBCO and YBCO, which has a transition temperature of about -181 degrees Celsius. MagLab engineers developed a windable tape out of YBCO and used it in a magnet that broke the world record in 2017 for an HTS coil operating inside a high-field resistive magnet.
A newly available superconducting material – a steel tape coated with a compound called yttrium-barium-copper oxide, or YBCO – has allowed scientists to produce smaller, more powerful magnets. YBCO is used in another novel MagLab magnet. Projected to crush the existing world record for the strongest superconducting magnet when completed in 2017, the 32-tesla magnet will feature about 6 miles of YBCO tape. Like the Platypus, it will combine high-temperature and low-temperature superconducting magnet coils. YBCO is also currently in use in numerous applications, including power transmission cables, motors, generators, bearings and microwave filters for cell phone towers.
Also called ferropnictides, iron-based superconductors (IBSCs) are iron-containing compounds that are relative newcomers to the high Tc family. They feature layers of iron and a pnictide, such as arsenic or phosphorus. Turns out it isn’t, and that IBSCs have properties that are helpful for turning them into current-carrying wires. They also have a respectable transition temperature (although not as high as the cuprates).
In 2019 Scientists reported to discover Superconductor might work at a record-breaking 200° Celsius
Scientists have calculated that a hydrogen-rich compound could conduct electricity without resistance at temperatures up to about 200° Celsius — well above the 100° C boiling point of water. If that prediction is confirmed experimentally, the material would stand in stark contrast to all other known superconductors, which must be cooled below room temperature to work (SN: 12/15/15).
The newly predicted superconductor — a compound of hydrogen, magnesium and lithium — comes with its own complications, however. It must be squeezed to extremely high pressure, nearly 2.5 million times the pressure of Earth’s atmosphere, physicist Hanyu Liu and colleagues, of Jilin University in Changchun, China, report in the Aug. Physical Review Letters.
Scientists previously have used similar techniques to predict that a pressurized compound of lanthanum and hydrogen would be superconducting at higher temperatures than any yet known. That prediction seems likely to be correct: In 2018, physicist Russell Hemley and colleagues reported signs that the compound is superconducting up to a record-breaking −13° C (SN: 9/10/18).
“This is an important prediction using a level of theory that has proven quite accurate,” says Hemley, of the University of Illinois at Chicago, who was not involved in the research.
In Oct 2020, University of Rochester engineers and physicists have, for the first time, created material that is superconducting at room temperature.
Compressing simple molecular solids with hydrogen at extremely high pressures, University of Rochester engineers and physicists have, for the first time, created material that is superconducting at room temperature. Featured as the cover article in the journal Nature, the work was conducted by the lab of Ranga Dias, an assistant professor of mechanical engineering and of physics and astronomy.
In setting the new record, Dias and his research team combined hydrogen with carbon and sulfur to photochemically synthesize simple organic-derived carbonaceous sulfur hydride in a diamond anvil cell, a research device used to examine miniscule amounts of materials under extraordinarily high pressure. The carbonaceous sulfur hydride exhibited superconductivity at about 58 degrees Fahrenheit and a pressure of and a pressure of about 39 million pounds per square inch (psi). “Because of the limits of low temperature, materials with such extraordinary properties have not quite transformed the world in the way that many might have imagined. However, our discovery will break down these barriers and open the door to many potential applications,” says Dias, who is also affiliated with the University’s materials science and high-energy-density physics programs.
Previously, the highest temperature for a superconducting material was achieved last year in the lab of Mikhail Eremets at the Max Planck Institute for Chemistry in Mainz, Germany, and the Russell Hemley group at the University of Illinois at Chicago. That team reported superconductivity at -10 to 8 degrees Fahrenheit using lanthanum superhydride.
However, hydrogen—the most abundant element in the universe —also offers a promising building block. “To have a high temperature superconductor, you want stronger bonds and light elements. Those are the two very basic criteria,” Dias says. “Hydrogen is the lightest material, and the hydrogen bond is one of the strongest. “Solid metallic hydrogen is theorized to have high Debye temperature and strong electron-phonon coupling that is necessary for room temperature superconductivity,” Dias says. However, extraordinarily high pressures are needed just to get pure hydrogen into a metallic state, which was first achieved in a lab in 2017 by Harvard University professor Isaac Silvera and Dias, then a postdoc in Silvera’s lab.
Dias’s lab at Rochester has pursued a “paradigm shift” in its approach, using as an alternative, hydrogen-rich materials that mimic the elusive superconducting phase of pure hydrogen, and can be metalized at much lower pressures. First the lab combined yttrium and hydrogen. The resulting yttrium superhydride exhibited superconductivity at what was then a record high temperature of about 12 degrees Fahrenheit and a pressure of about 26 million pounds per square inch.
Next the lab explored covalent hydrogen-rich organic-derived materials. This work resulted in the carbonaceous sulfur hydride. “This presence of carbon is of tantamount importance here,” the researchers report. Further “compositional tuning” of this combination of elements may be the key to achieving superconductivity at even higher temperatures, they add.Other coauthors on the paper include lead author Elliot Snider ’19 (MS), Nathan Dasenbrock-Gammon ’18 (MA), Raymond McBride ’20 (MS), Kevin Vencatasamy ’21, and Hiranya Vindana (MS), all of the Dias lab; Mathew Debessai of Intel Corporation, and Keith Lawlor of the University of Nevada Las Vegas.
The project was supported with funding from the National Science Foundation and the US Department of Energy’s Stockpile Stewardship Academic Alliance Program and its Office of Science, Fusion Energy Sciences. Preparation of the diamond surfaces was performed in part at the University of Rochester Integrated Nanosystems Center (URnano). Dias and Salamat have started a new company, Unearthly Materials to find a path to room temperature superconductors that can be scalably produced at ambient pressure.
In feb 2019 it was reported that Navy filed for patent on room-temperature superconductor
Salvatore Cezar Pais , a scientist working for the U.S. Navy has filed for a patent on a room-temperature superconductor, representing a potential paradigm shift in energy transmission and computer systems. The application claims that a room-temperature superconductor can be built using a wire with an insulator core and an aluminum PZT (lead zirconate titanate) coating deposited by vacuum evaporation with a thickness of the London penetration depth and polarized after deposition.
An electromagnetic coil is circumferentially positioned around the coating such that when the coil is activated with a pulsed current, a non-linear vibration is induced, enabling room temperature superconductivity. “This concept enables the transmission of electrical power without any losses and exhibits optimal thermal management (no heat dissipation),” according to the patent document, “which leads to the design and development of novel energy generation and harvesting devices with enormous benefits to civilization.”
In 2018 Scientists found Graphene on the way to superconductivity
Graphene, the exotic, strictly two-dimensional material conducts electricity well, but is not a superconductor. But scientists at HZB have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance. They probed the band structure at BESSY II with extremely high resolution ARPES and could identify a flat area at a surprising location. Their research is published in Science Advances.
In April 2018, a group at MIT in the U.S. 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 at a 1.1 degree angle. 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.
At BESSY II, the physicists are able to scan the so-called band structure of the sample. This band structure provides information on how the charge carriers are distributed among the quantum-mechanically permitted states and which charge carriers are available for transport at all. The angle-resolved photoemission spectroscopy (ARPES) at BESSY II enables such measurements with extremely high resolution.
Via an exact analysis of the band structure, they identified an area that had previously been overlooked. “The double layer of graphene has been studied before because it is a semiconductor with a band gap,” explains Varykhalov. “But on the ARPES instrument at BESSY II, the resolution is high enough to recognize the flat area next to this band gap.”
“It is an overseen property of a well-studied system,” says first author Dr. Dmitry Marchenko. “It was previously unknown that there is a flat area in the band structure in such a simple well-known system.”
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 physicists have found that the interactions between the two graphene layers and between graphene and the silicon carbide lattice are jointly responsible for the formation of the flat band area. “We can predict this behavior with very few parameters and could use this mechanism to control the band structure,” adds Oliver Rader.
In June 2019 National MagLab created world-record magnetic field with small, compact coil
The miniature magnet created by Hahn and his team generated a world-record 45.5 tesla magnetic field. A typical hospital MRI magnet is about 2 or 3 teslas, and the strongest, continuous-field magnet in the world is the MagLab’s own 45-tesla hybrid instrument, a 35-ton behemoth that has maintained that record since 1999.
The 45-T, as it is called, is still the world’s strongest working magnet, enabling cutting-edge physics research into materials. But in a test, the half-pint-sized magnet invented by Hahn, tipping the scales at 390 grams (0.86 pounds), briefly surpassed the reigning champ’s field by half a tesla, a compelling proof of concept.
This new magnet is a plucky David to the MagLab’s conventional Goliaths, said National MagLab Director Greg Boebinger. “This is indeed a miniaturization milestone that could potentially do for magnets what silicon has done for electronics,” he said. “This creative technology could lead to small magnets that do big jobs in places like particle detectors, nuclear fusion reactors and diagnostic tools in medicine.”
Both the 45-T magnet and the 45.5-T test magnet are built in part with superconductors, a class of conductors boasting special properties, including the ability to carry electricity with perfect efficiency. The superconductors used in the 45-T are niobium-based alloys, which have been around for decades. But in the 45.5-T proof-of-principle magnet, Hahn’s team used a newer compound called REBCO (rare earth barium copper oxide) with many advantages over conventional superconductors.
Notably, REBCO can carry more than twice as much current as a same-sized section of niobium-based superconductor. This current density is crucial: After all, the electricity running through an electromagnet generates its field, so the more you can cram in, the stronger the field. Also critical was the specific REBCO product used—paper-thin, tape-shaped wires manufactured by SuperPower Inc.
With the guidance of veteran MagLab engineer Iain Dixon, the team built three increasingly powerful prototypes in quick succession that became known as the Little Big Coil (LBC) series.
“The fundamental problem of REBCO is that it’s a single-filament conductor that cannot be made perfectly,” Larbalestier said. “So any length of conductor contains a variety of defects whose impact on any future magnet is not yet well understood. “That was discovered beautifully in these experiments,” Larbalestier said. “We found a way to control this damage, which is to insist that we buy material that has one non-slit edge, and we orient the non-slit edge away from the center of the magnet. And under these circumstances, so far we are not seeing damage.”
Due to production constraints, REBCO tapes are manufactured at a specific width —12 mm, or about half an inch. To meet the LBC’s requirements, however, those tapes had to be cut lengthwise to 4 mm wide. That’s difficult to do, even with the greatest care, because REBCO is quite brittle.
Today’s electromagnets contain insulation between conducting layers, which directs the current along the most efficient path. But it also adds weight and bulk. Hahn’s innovation: A superconducting magnet without insulation. In addition to yielding a sleeker instrument, this design protects the magnet from a malfunction known as a quench. Quenches can occur when damage or imperfections in the conductor block the current from its designated path, causing the material to heat up and lose its superconducting properties. But if there is no insulation, that current simply follows a different path, averting a quench.
“The fact that the turns of the coil are not insulated from each other means that they can share current very easily and effectively in order to bypass any of these obstacles,” explained Larbalestier, corresponding author on the Nature paper. There’s another slimming aspect of Hahn’s design that relates to quenches: Superconducting wires and tapes must incorporate some copper to help dissipate heat from potential hot spots. His “no-insulation” coil, featuring tapes a mere 0.043-mm thick, requires much less copper than do conventional magnets.