Inside a clean room, Brookhaven physicists Ivan Bozovic (left) and Anthony Bollinger work on the molecular beam epitaxy system that produced the atomically perfect materials used in the study. | Photo courtesy of Brookhaven National Lab
How does it work?
- Intense laser pulses called “pumps” cause excitations in the superconducting films.
- Pumps are then probed by measuring the film reflectance with a second light pulse — this is called a pump-probe process.
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 are striving to better understand superconductors and build out their properties so that they operate at even higher temperatures. Recently, two studies by two different research teams at Brookhaven National Laboratory have shown new insights into how superconductors overcome resistance, one involving a wave ... and the other a directional doper.
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.
