title: Quantum oscillations of nitrogen atoms in uranium nitride.
abstract: The vibrational excitations of crystalline solids corresponding to acoustic or optic one-phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride, showing well-defined, equally spaced, high-energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use uranium nitride as a fuel.
authors.affiliation: Quantum Condensed Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. aczelaa@ornl.gov
authors.forename: A A
authors.initials: AA
authors.lastname: Aczel
authors.forename: G E
authors.initials: GE
authors.lastname: Granroth
authors.forename: G J
authors.initials: GJ
authors.lastname: Macdougall
authors.forename: W J L
authors.initials: WJ
authors.lastname: Buyers
authors.forename: D L
authors.initials: DL
authors.lastname: Abernathy
authors.forename: G D
authors.initials: GD
authors.lastname: Samolyuk
authors.forename: G M
authors.initials: GM
authors.lastname: Stocks
authors.forename: S E
authors.initials: SE
authors.lastname: Nagler
mesh_terms: D009584:Nitrogen / Q000737:chemistry*; D017974:Uranium Compounds / Q000737:chemistry*; D014732:Vibration
chemical_list: D017974:Uranium Compounds; D009584:Nitrogen