Overcoming Resistance and Lighting Up the World

Photo courtesy of Brookhaven National Laboratory

Scientists have found that the substitution of cobalt atoms into the crystal framework of an iron-based material-which is required to convert the material from a magnet into a superconductor-also introduces elongated impurity states at each cobalt atom (note the directional alignment of "twin" peaks around each cobalt atom in the electronic structure map). These elongated impurities then scatter electrons in an asymmetric way that explains many of the material's unusual properties, and could eventually lead to the design of new types of superconductors for practical applications in energy transmission and storage.

In a sense, the story of science is the story of successfully overcoming resistance. There are usually uncertain data sets, errant hypotheses and frankly, things that simply go wrong.

That quest to overcome resistance is literally true in the study of superconductors. Superconductors are just that: Materials that carry electrical current with little or no resistance. They're of great interest since electricity is usually carried with cost – a significant fraction that goes through transmission lines is typically lost. And despite their use in technologies such as MRI's and Maglev trains, superconductors are also costly, complex materials that require real cooling before the free flow of current kicks in. That's true even for high-temperature superconductors (HTSs), which only operate at frozen temperatures far below the comfort level of penguins or polar bears.

As a consequence, researchers supported by the Office of Science are striving to better understand superconductors and build out their properties so that they operate at even higher temperatures. (Dr. Amit Goyal, of the Office of Science's Oak Ridge National Laboratory, gave a Science Lecture on this topic last May http://www.youtube.com/watch?v=S89fVk5HXLs&feature=youtu.be.) Recently, two studies by two different research teams at the Office of Science's Brookhaven National Laboratory (Brookhaven Lab) have shown new insights into how superconductors overcome resistance, one involving a wave . . . and the other a directional doper.

Enlarge Photo

Photo courtesy of Brookhaven National Laboratory

Physicists Anthony Bollinger (left) and Ivan Bozovic working at a thin film deposition device in Brookhaven Lab's Condensed Matter Physics and Materials Science Department.

In the first study, a team at Brookhaven Lab and the Massachusetts Institute of Technology (MIT) used lasers to examine one possible cause of high-temperature superconductivity, fleeting and sometimes fluctuating phenomena called charge-density waves (CDWs). CDWs are akin to waves on a lake, with electrons rolling across thin, copper containing films but in this case they are fleeting, lasting a mere two picoseconds – a millionth of a millionth of a second – or less. Researchers confirmed the existence of the waves (though made no comment on what would likely be exceptionally short surfing contests on them). However, to their surprise, scientists found CDWs in only one of two superconducting samples, suggesting that other factors may be responsible.

Doping is almost certainly one of them. Doping is definitely a bad idea when it comes to baseball and biking, but a different team of researchers at the lab – joined by counterparts at Cornell University and other collaborators – discovered why doping may be critical to the super (conductive) performance of some materials in a couple of different ways. Specifically, they looked at an iron-based compound, which becomes a superconductor when cobalt atoms replace iron atoms at different points. Scientists showed that cobalt doping not only increased the number of electrons – which may assist in unleashing superconductivity – but also seemed to force directionality, allowing electrical current traveling easily in one direction of the superconducting material, but meeting resistance in the other.

Attempts to overcome all forms of resistance may be, well, futile (it had to come somewhere). But this duo of studies opens new possibilities in a fast-moving field already full of potential. That's the Office of Science at work: Overcoming resistance . . . and lighting up the world.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about Brookhaven Lab, please go to http://www.bnl.gov/world/.

Charles Rousseaux is a Senior Writer in the Office of Science.