For more than 50 years, scientists have debated what turns particular oxide insulators, in which electrons barely move, into metals, in which electrons flow freely. Some scientists sided with Nobel Prize–winning physicist Nevill Mott in thinking direct interactions between electrons were the key. Others believed, as did physicist Rudolf Peierls, that atomic vibrations and distortions trumped all. Now, a team led by the U.S. Dept. of Energy (DOE)’s Oak Ridge National Laboratory (ORNL) has made an important advancement in understanding a classic transition-metal oxide, vanadium dioxide, by quantifying the thermodynamic forces driving the transformation. The results are published in Nature.
“We proved that phonons—the vibrations of the atoms—provide the driving force that stabilizes the metal phase when the material is heated,” said John Budai, who co-led the study with Jiawang Hong, a colleague in ORNL’s Materials Science and Technology Div.