 A stylized rendition of an infrared nanoscope illustrates how concentrated infrared illumination finely focuses upon a field just 20-billionths of a meter wide to view metallic puddles in vanadium dioxide as the material begins to transform from an electrically insulating state to an electrically conducting one. | Collaboration yields 'the right glasses' for observing mystery behavior in electrons. Images provide clues to Mott transition in semi- and superconductors. LOS ALAMOS, New Mexico, December 13, 2007—In collaboration with the Center for Integrated Nanotechnologies at Los Alamos, an international team of researchers has, for the first time, viewed on a nanoscale the formation of mysterious metallic puddles that facilitate the transition of an electrically insulating material into an electrically conducting one. The research may lead to a better understanding of superconductors—materials that conduct electricity without energy loss—or development of better materials for powering high-speed electronics. |
Materials such as copper metal contain electrons that are mobile enough to conduct an electrical current. In conducting materials such as copper or aluminum, electrons do not hinder one another and are free to move about the lattice structure of the material. In more-complex crystal oxides, such as vanadium dioxide, electrons can become influenced by nearby positively or negatively charged particles, and their movement can become hindered. These materials are known by physicists as “correlated materials.”
 The image shows Infrared snapshots taken during the critical temperature range of the Mott transition of vanadium dioxide. The blue portion of the images show the material while in an electrically insulating state. As the temperature increases through the Mott transition zone, green areas show the formation of metallic puddles in the material. The transition from insulator to conductor is clearly proceeded by temperature-induced growth and coalescence of initially separate metallic puddles. | Correlated materials include superconductors or semiconductors—crystals peppered or “doped” with atoms that may donate mobile electrons to the solid. Correlated materials can exhibit extraordinary changes in their physical properties, such as transforming from an insulating material to a conducting material, when subjected to relatively small changes in pressure or temperature. Vanadium dioxide begins to transform itself from an insulator to a conductor when heated above 341 degrees Kelvin (about 154 degrees Fahrenheit or 68 degrees Celsius). For decades scientists have puzzled over how this transformation to a fully metallic state—known as “Mott” metal-insulator transition—occurs. Balatsky, a Los Alamos condensed-matter theorist, believed, like many other scientists, that the transition begins when metallic puddles begin forming at sites of impurities or imperfections within the lattice. The puddles grow until they touch, and at that point the material becomes conductive, or superconductive. “We had evidence to believe that metallic puddles were forming in an inhomogenous manner within the material at the transition phase, but we had no way of proving it,” said Balatsky. “If you had the right glasses that could see something extremely small, you could see this process occurring.” |
Using this nanoscale viewer, the UCSD-LANL-Max Planck-ETRI team was able to watch metallic puddles form within vanadium oxide at the exact temperature where the Mott transition was expected to occur. These “infrared nanoscope” images have revealed for the first time a new type of metal “phase” existing only during the transition of the material from its insulating state to its conducting state.
The new findings will help researchers worldwide better describe and understand underlying physical laws of how charges propagate through correlated materials.
The research could help materials scientist understand how to precisely dope a material with specific atoms in order to optimize conducting or superconducting behavior or, conversely, to create materials impervious to electrical conductivity or magnetic influences.
“What is extremely exciting about this research is that four different laboratories with complementary disciplines cooperated to use this infrared nanoscope in its first successful application for solving a solid-state physics puzzle,” Keilmann said. ###
About Los Alamos National Laboratory (www.lanl.gov)
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, BWX Technologies, and Washington Group International for the Department of Energy’s National Nuclear Security Administration.
Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.
Los Alamos National Laboratory/Sandia National Laboratories’ Center for Integrated Nanotechnologies is one of five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize, and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The other four NSRCs are located at DOE's Argonne, Brookhaven, Lawrence Berkeley and Oak Ridge National Laboratories. For more information about the DOE NSRCs, please visit nano.energy.gov.
Contact: James E. Rickman jamesr@lanl.gov 505-665-9203 DOE/Los Alamos National Laboratory
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