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Physicists have been interested in the 'problem' of heavy fermions -- why these electrons act as if they are hundreds or thousands of times more massive under certain conditions -- for thirty or forty years.
In this material -- synthesized by Graeme Luke's group at McMaster -- the effects of heavy fermions begin to appear as the material is cooled below 55 kelvin (-218 °C). Then, an even more unusual electronic phase transition occurs below 17.5K.
Scientists had attributed this lower-temperature phase transition to some form of "hidden order." They could not distinguish whether it was related to the collective behavior of electrons acting as a wave, or interactions of individual electrons with the uranium atoms.
Alexander Balatsky, a Los Alamos theoretical physicist at the Center for Integrated Nanotechnologies, provided guidance on how to examine this problem. With that guidance, Davis' group used a technique they'd designed to visualize the behavior of electrons to "see" what the electrons were doing as they passed through the mysterious phase transition.
The technique, spectroscopic imaging scanning tunneling microscopy (SI-STM), measures the wavelength of electrons on the surface of the material in relation to their energy.
"Imagine flying over a body of water where standing waves are moving up and down, but not propagating toward the shore," said Davis. "When you pass over high points, you can touch the water; over low points, you can't. This is similar to what our microscope does. It images how many electrons can jump to the tip of our probe at every point on the surface."