In many substances, slight differences in the vibrations of just a few constituent atoms can have important effects on macroscopic material properties. For example, the vibrational motion of impurities can determine whether a material is useful as a conductor or semiconductor. Now, a group of researchers in Japan has developed a method to determine the phonon density of states for different sites in a material, even when the difference involves only dissimilar states or environments of otherwise identical atoms. The physicists used a refinement of nuclear resonant inelastic scattering to measure not only phonon energy spectra but also the hyperfine interactions between nuclei and the surrounding electronic states. As a demonstration at Japan’s SPring-8 synchrotron source, the group studied iron atoms in magnetite; two-thirds of those atoms are surrounded by six oxygen atoms and the remaining iron atoms are surrounded by four oxygens. Oscillations in the gamma radiation signal clearly...

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