XAFS and x-ray and neutron pdfs from UO2, U4O9, and U3O7 find U-O multisite distributions in the x-ray and simple distributions in the neutron measurements. This putative contradiction indicates a dynamical character and breakdown of the Born-Oppenheimer approximation for the �super� polaron in urania. Together with the apparent homogeneity of the O K edge XAS for these compounds, these results suggest that the ground state fluorite structure intersects a low lying, uranyl-type of excited state in a conic intersection. We have also performed ultrafast pump-probe reflectivity and THz measurements on UO2 that show that the photoinduced quasiparticles condense into a new phase with the opening of a gap of currently unknown character at 50�60 K, above the 30 K AFM transition. The quasiparticle condensate appears to be separate from spin ordering. Summarizing, the interactions of charge inhomogeneities with the UO2 lattice are exceedingly complicated and point to new physics.

Identification and characterization of a dynamical charge-lattice instability in UO<sub>2</sub>

243rd National Meeting (2012)

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Identification and characterization of a dynamical charge-lattice instability in UO2

Identification and characterization of a dynamical charge-lattice instability in UO₂