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.

Robert Fisher and Cal Jordan are among a team of scientists who will expend 22 million computational hours during the next year on one of the world’s most powerful supercomputers, simulating an event that takes less than five seconds.

Fisher and Jordan require such resources in their field of extreme science. Their work at the University of Chicago’s Center for Astrophysical Thermonuclear Flashes explores how the laws of nature unfold in natural phenomena at unimaginably extreme temperatures and pressures. The Blue Gene/P supercomputer at Argonne National Laboratory will serve as one of their primary tools for studying exploding stars.

A snapshot of a three-dimensional simulation of a Type Ia supernova, shortly after the nuclear flame bubble that initiates the Ia event is ignited slightly off-center from the progenitor white dwarf star (shown here as a light blue surface). Buoyancy forces drive the bubble (shown in yellow and red) rapidly to the surface of the white dwarf. The bubble, consisting of nuclear ash heated to hundreds of millions of degrees, reaches a speed of nearly 2 million miles per hour before erupting from the surface roughly a second after ignition.

“The Argonne Blue Gene/P supercomputer is one of the largest and fastest supercomputers in the world,” said Fisher, a Flash Center Research Scientist. “It has massive computational resources that are not available on smaller platforms elsewhere.”

Desktop computers typically contain only one or two processors; Blue Gene/P has more than 160,000 processors. What a desktop computer could accomplish in a thousand years, the Blue Gene/P supercomputer can perform in three days. “It’s a different scale of computation. It’s computation at the cutting edge of science,” Fisher said.

Access to Blue Gene/P, housed at the Argonne Advanced Leadership Computing Facility, was made possible by a time allocation from the U.S. Department of Energy’s Innovative and Novel Computational Impact on Theory and Experiment program. The Flash Center was founded in 1997 with a grant from the National Nuclear Security Administration’s Office of Advanced Simulation and Computing. The NNSA’s Academic Strategic Alliance Program has sustained the Flash Center with funding and computing resources throughout its history.

A snapshot of a Type Ia supernova simulation taken very shortly after the moment of detonation. The energy released during the detonation is equivalent to 1,027 hydrogen bombs, each equivalent to 100 megatons of TNT. This tremendous energy release makes Type Ia supernovae some of the most intrinsically luminous explosions in the universe, and therefore useful as distance indicators for cosmology.

The support stems from the DOE’s interest in the physics that take place at extremes of concentrated energy, including exploding stars called supernovas. The Flash Center will devote its computer allocation to studying Type Ia supernovas, in which temperatures reach billions of degrees.

A better understanding of Type Ia supernovas is critical to solving the mystery of dark energy, one of the grandest challenges facing today’s cosmologists. Dark energy is somehow causing the universe to expand at an accelerating rate.
Cosmologists discovered dark energy by using Type Ia supernovas as cosmic measuring devices. All Type Ia supernovas display approximately the same brightness, so scientists could assess the distance of the exploding stars’ home galaxies accordingly. Nevertheless, these supernovas display a variation of approximately 15 percent.

“To really understand dark energy, you have to nail this variation to about 1 percent,” said Jordan, a Flash Center Research Associate.

The density of white dwarf stars, from which Type Ia supernovas evolve, is equally extreme. When stars the size of the sun reach the ends of their lives, they have shed most of their mass and leave behind an inert core about the size of the moon. “If one were able to scoop out a cubic centimeter—roughly a teaspoon—of material from that white dwarf, it would weigh a thousand metric tons,” Fisher explained. “These are incredibly dense objects.”

Type Ia supernovas are believed to only occur in binary star systems, those in which two stars orbit one another. When a binary white dwarf has gravitationally pulled enough matter off its companion star, an explosion ensues.

“This takes place over hundreds of millions of years,” Jordan said. “As the white dwarf becomes more and more dense with matter compressing on top of it, an ignition takes place in its core. This ignition burns through the star and eventually leads to a huge explosion.”

The Flash team conducts whole-star simulations on a supercomputer at Lawrence Berkeley National Laboratory in California. At Argonne, the team will perform a related set of simulations. “You can think of them as a nuclear ‘flame in a box’ in a small chunk of the full white dwarf,” Fisher said.

In the simulations at Argonne, the team will analyze how burning occurs in four possible scenarios that lead to Type Ia supernovas. Burning in a white dwarf can occur as a deflagration or as a detonation.

“Imagine a pool of gasoline and throw a match on it. That kind of burning across the pool of gasoline is a deflagration,” Jordan said. “A detonation is simply if you were to light a stick of dynamite and allow it to explode.”

In the Flash Center scenario, deflagration starts off-center of the star’s core. The burning creates a hot bubble of less dense ash that pops out the side due to buoyancy, like a piece of Styrofoam submerged in water. But gravity holds the ash close to the surface of the white dwarf. “This fast-moving ash stays confined to the surface, flows around the white dwarf and collides on the opposite side of breakout,” Jordan said.

The collision triggers a detonation that incinerates the star. There are, however, three other scenarios to consider. “To understand how the simulations relate to the actual supernovae, we have to do more than a thousand different simulations this year to vary the parameters within the models to see how the parameters affect the supernovae,” Jordan said.