Trunkneck’s Blog

Superconductivity has perplexed, astounded and inspired scientists ever since it was discovered in 1911. Now, in the latest of a century of surprises, researchers at the National High Magnetic Field Laboratory at Florida State University have discovered unusual properties in a novel superconducting material that point to an entirely new kind of superconductor.

A hybrid scanning laser plus color confocal microscope image of a cleaved fluorine-doped lanthanum oxide iron arsenide sample.

Frank Hunte, a postdoctoral associate at the lab’s Applied Superconductivity Center (ASC), working with David Larbalestier, Alex Gurevich and Jan Jaroszynski, and colleagues in David Mandrus’ group at Oak Ridge National Laboratory in Tennessee, discovered surprising magnetic properties in the new superconductors that suggest they may have very powerful applications — from improved MRI machines and research magnets to a new generation of superconducting electric motors, generators and power transmission lines. The research also adds to the long list of mysteries surrounding superconductivity, providing evidence that the new materials, which scientists are calling “doped rare earth iron oxyarsenides,” develop superconductivity in quite a new way, as detailed in the latest issue of the prestigious journal Nature.

A scanning laser confocal microscope-generated image of the surface of a cleaved fluorine-doped lanthanum oxide iron arsenide sample.

Though research on this substance is very much in its early stages, scientists are talking excitedly of “promise” and “potential.”

“What one would like is a greater selection of superconductors, operating at higher temperatures, being cheaper, possibly being more capable of being made into round wires,” said Larbalestier, director of the ASC. “Iron and arsenic, both inherently cheap materials, are key constituents of this totally new class of superconductors. We’re just fascinated. It’s superconductivity in places you never thought of.”

Frank Hunte, a postdoctoral associate at the National High Magnetic Field Laboratory’s Applied Superconductivity Center (ASC), working with colleagues from the ASC in Tallahassee, Fla., and Oak Ridge National Laboratory in Tennessee, discovered surprising magnetic properties in the new superconductors that suggest they may have very powerful applications — from improved MRI machines and research magnets to a new generation of superconducting electric motors, generators and power transmission lines.

Superconductivity can be thought of as “frictionless” electricity. In conventional electricity, heat is generated by friction as electrons (electric charge carriers) collide with atoms and impurities in the wire. This heating effect is good for appliances such as toasters or irons, but not so good for most other applications that use electricity. In superconductors, however, electrons glide unimpeded between atoms without friction. If scientists and engineers ever harness this phenomenon at or near room temperature in a practical way, untold billions of dollars could be saved on energy costs.

“What one would like is a greater selection of superconductors, operating at higher temperatures, being cheaper, possibly being more capable of being made into round wires,” said David Larbalestier, director of the Applied Superconductivity Center at Florida State University. “Iron and arsenic, both inherently cheap materials, are key constituents of this totally new class of superconductors. We’re just fascinated. It’s superconductivity in places you never thought of.”

That’s a big if. Superconductivity, though promising, is still impractical in routine engineering use because it requires a very cold environment attainable only with the help of expensive cryogens such as liquid helium or liquid nitrogen. Past discoveries have helped scientists inch their way up the thermometer, from superconductors requiring minus 452 degrees Fahrenheit (or 4.2 Kelvin) to newer materials that superconduct at around minus 200 degrees F (138 K) — still frigid, but substantially warmer and more practical.

Early this year, Japanese scientists who had been developing iron-based superconducting compounds for several years finally tweaked the recipe just right with a pinch of arsenic. The result: a superconductor, also featuring oxygen and the rare earth element lanthanum, performing at a promising minus 413 degrees F (26 K). The presence of iron in the material was another scientific stunner: Because it’s ferromagnetic, iron stays magnetized after exposure to a magnetic field, and any current generates such a field. As a rule, magnetism’s effect on superconductivity is not to enhance it, but to kill it.

The National High Magnetic Field Laboratory’s 45-tesla Hybrid magnet, which produces the highest field of any continuous field magnet in the world, was used to measure how high a magnetic field the new superconducting material could tolerate.

Teams of scientists quickly got busy synthesizing and studying various iron oxyarsenides. Larbalestier, eager to get in on the research, secured a sample from colleagues at Oak Ridge. His objective: Put it in the magnet lab’s 45-tesla Hybrid magnet to see how high a magnetic field the new material could tolerate. (Tesla is a unit of magnetic field strength; the Earth’s magnetic field is one twenty thousandth of a tesla.)

Hunte and his colleagues thought the world-record Hybrid magnet would be more than sufficient to test the field tolerance limits of the new material. They thought wrong: The iron oxyarsenide kept superconducting all the way up to 45 tesla, far past the point at which other superconductors become normal conductors.
A high tolerance for magnetic field is one of three key properties researchers hope for in superconductors. Also desirable are the abilities to operate at relatively high temperatures and in the presence of high electrical currents. Superconductors are used to make MRI and research magnets, and now they are being tested in a new generation of superconducting electric motors, generators, transformers and power transmission lines. Today, the most powerful superconducting magnet generates a field of about 26 tesla. If a superconductor could be found that tolerates a higher current and field, it may make possible more powerful magnets, opening up vast new research areas to scientists and power applications.

Hunte’s experiment yielded other tantalizing findings. Although scientists discovered half a century ago that superconducting electrons enter the “Cooper pair” state, pairing with opposite spin and momentum, magnetism was always thought to break such pairs. Now the archetypal magnetic atom, iron, is a key part of this new class of high temperature superconductors. Scientists have yet another puzzle to probe.

“So far,” said Hunte, “based on both theoretical calculations and what we’re seeing from the experiments, it seems likely that this is a completely different mechanism for superconductivity.”

Hunte is quick to say the group’s research barely scratches the surface.

“The field is completely open. No one knows where this is going to go,” Hunte said. “If it’s found that these materials can support high current densities, then they could be tremendously useful.”

The National High Magnetic Field Laboratory develops and operates state-of-the-art, high-magnetic-field facilities that faculty and visiting scientists and engineers use for research. The laboratory, which is operated by a consortium composed of Florida State University, the University of Florida and Los Alamos National Laboratory, is sponsored by the National Science Foundation and the state of Florida.

Like a team of forensic detectives in a television show that could be called “CSI: Milky Way,” a University of Chicago astrophysicist and his associates are piecing together how a mysterious infrared ring got left around a dead star that displays a magnetic field trillions of times more intense than Earth’s.

This image shows a ghostly ring extending seven light-years across around the corpse of a massive star. The collapsed star, called a magnetar, is located at the exact center of this image. NASA’s Spitzer Space Telescope imaged the mysterious ring around magnetar SGR 1900 14 in infrared light. The magnetar itself is not visible in this image, as it has not been detected at infrared wavelengths (it has been seen in X-ray light).

NASA’s Spitzer Space Telescope detected the ring around magnetar SGR 1900+14 at two narrow infrared frequencies in 2005 and 2007. The ringed magnetar is of a type called a soft gamma repeater (SGR) because it repeatedly emits bursts of gamma rays.

“The universe is a big place, and weird things can happen,” said Stephanie Wachter of NASA’s Spitzer Science Center at the California Institute of Technology. “I was flipping through archived Spitzer data of the object, and that’s when I noticed it was surrounded by a ring we’d never seen before.”

Wachter enlisted Vikram Dwarkadas, a Senior Research Associate in Astronomy & Astrophysics at the University of Chicago, to help determine how the ring formed. Wachter, Dwarkadas and five other co-authors present the results of their investigation in the May 29 issue of the journal Nature.

“It’s the first time something like this has ever been seen around a magnetar,” Dwarkadas said. Magnetars come from massive stars that have exploded as a core-collapse supernova. “These stars are at least eight times the mass of the sun, or more massive than that,” he said.

Magnetars interest astrophysicists because of their mysterious and unusual characteristics. When massive stars collapse, they usually form compact objects called neutron stars or black holes. “We have no idea why some neutron stars are magnetars and some are not,” Dwarkadas said.

SGR 1900+14 seems to belong to a nearby cluster of massive stars that resides along the plane of the Milky Way. Since the most massive stars live the shortest lives, the object hints that perhaps only the most massive stars become magnetars.

When Wachter’s team began pondering the origin of the ring, “We thought initially of all the standard explanations,” Dwarkadas said. But the team considered and eliminated several possibilities before concluding that a powerful flare that burst from the magnetar formed the ring, which measures seven light-years across.

“It’s as if the magnetar became a huge flaming torch and obliterated the dust around it, creating a massive cavity,” said co-author Chryssa Kouveliotou, senior astrophysicist at NASA’s Marshall Space Flight Center in Alabama. “Then the stars nearby lit up a ring of fire around the dead star, marking it for eternity.”

Vikram Dwarkadas, Senior Research Associate in Astronomy & Astrophysics at the University of Chicago. Along with colleagues at NASA and elsewhere, Dwarkadas has been studying a strange ring circling a dead star.

A theoretical astrophysicist supported by the National Science Foundation and NASA, Dwarkadas specializes in various phenomena related to supernova remnants and stellar winds. He helped Wachter’s team systematically eliminate several potential causes for the ring.

Was the ring an infrared echo, a mass of dust lit up by a flare moving out from the magnetar? The 2007 Spitzer image showed no discernable change in the ring after two years. “If it hasn’t moved, it hasn’t changed, it can’t be an infrared echo,” Dwarkadas said. “It’s a stationary ring.”

Could the ring be a bubble blown by solar winds emitted from the star before it exploded? Shock waves of a supernova travel at approximately 10,000 miles a second. If the ring was a wind-blown bubble, the supernova shock wave would overtake it somewhere between a few decades to a century or two, at most.

“It would mean that the supernova should have actually gone through and destroyed the ring unless it was very, very recent,” Dwarkadas said. If the ring was a wind-blown bubble that somehow survived the supernova shock wave, “then you’d need a massive bubble,” he said. “We did some calculations and we ran some simulations, and it just didn’t work.”

Wachter’s team next considered whether the ring could be related to the supernova. That possibility also failed to pan out. “If there is a supernova, there would be shocks. You would see X-ray, radio and optical emission. We looked at archival data, and there was no emission at any wavelength except in the Spitzer images,” Dwarkadas said.

The paper’s other co-authors are Jonathan Granot of the University of Hertfordshire, England; Enrico Ramirez-Ruiz of the University of California, Santa Cruz; Sandy Patel of the Optical Sciences Corporation, Huntsville, Ala.; and Don Figer at the Rochester Institute of Technology in New York.