In the search for understanding how some magnetic materials can be transformed to carry electric current with no energy loss, scientists at the U.S. Department of Energy's Brookhaven National Laboratory, Cornell University, and collaborators have made an important advance: Using an experimental technique they developed to measure the energy required for electrons to pair up and how that energy varies with direction, they've identified the factors needed for magnetically mediated superconductivity—as well as those that aren't.
The material the team of researchers studied was discovered in part by Brookhaven physicist Cedomir Petrovic ten years ago, when he was a graduate student working at the National High Magnetic Field Laboratory. It's a compound of cerium, cobalt, and indium that many believe may be the simplest form of an unconventional superconductor—one that doesn't rely on vibrations of its crystal lattice to pair up current-carrying electrons. Unlike conventional superconductors employing that mechanism, which must be chilled to near absolute zero (-273 degrees Celsius) to operate, many unconventional superconductors operate at higher temperatures—as high as -130°C. Figuring out what makes electrons pair in these so-called high-temperature superconductors could one day lead to room-temperature varieties that would transform our energy landscape.
The main benefit of CeCoIn5, which has a chilly operating temperature (-271°C), is that it can act as the "hydrogen atom" of magnetically mediated superconductors, Davis said—a test bed for developing theoretical descriptions of magnetic superconductivity the way hydrogen, the simplest atom, helped scientists derive mathematical equations for the quantum mechanical rules by which all atoms operate.
The method, called quasiparticle scattering interference, uses a spectroscopic imaging scanning tunneling microscope designed by Davis to measure the strength of the "glue" holding electron pairs together as a function of the direction in which they are moving. If magnetism is the true source of electron pairing, the scientists should find a specific directional dependence in the strength of the glue, because magnetism is highly directional (think of the north and south poles on a typical bar magnet). Electron pairs moving in one direction should be very strongly bound while in other directions the pairing should be non-existent, Davis explained.
With the samples held in the microscope far below their superconducting temperature, the scientists sent in bursts of energy to break apart the electron pairs. The amount of energy it takes to break up the pair is known as the superconducting energy gap.
The instrument uses the finest energy resolution for electronic matter visualization of any experiment ever achieved to tease out incredibly small energy differences—increments that are a tiny fraction of the energy of a single photon of light. The precision measurements revealed the directional dependence the scientists were looking for in the superconducting energy gap.
One of the most important things the theory will do, the researcher explained, will be to help separate the "epiphenomena," or side effects, from the true phenomena—the fundamental elements essential for superconductivity.
This story is reprinted from material from Brookhaven National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.