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  • Conradson, Steven D.Inst Josef Stefan, Ljubljana 1000, Slovenia.;Washington State Univ, Pullman, WA 99164 USA. (author)

Closure of the Mott gap and formation of a superthermal metal in the Frohlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

  • Article/chapterEnglish2017

Publisher, publication year, extent ...

  • 2017
  • printrdacarrier

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  • LIBRIS-ID:oai:DiVA.org:uu-335203
  • https://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-335203URI
  • https://doi.org/10.1103/PhysRevB.96.125114DOI

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  • Language:English
  • Summary in:English

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  • Subject category:ref swepub-contenttype
  • Subject category:art swepub-publicationtype

Notes

  • Mixed valence O-doped UO2+x. and photoexcited UO2 containing transitory U3+ and U5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Frohlich-type, nonequilibrium, phononcoupled Bose-Einstein condensate whose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO2, U4O9, and U3O7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f states of the valence band by similar to 0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2-2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO2 therefore fulfills the criteria for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5-10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: (1) the direct formation of both of these long lived (> 3-10 ps) excited states without the short lived nonthermal intermediate; (2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and (3) the absence of hot electrons accompanying the insulating UO2 excited state. This heterogeneous, nonequilibrium, Frohlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.

Subject headings and genre

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  • Andersson, David A.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Boland, Kevin S.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Bradley, Joseph A.Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Univ Washington, Seattle, WA 98195 USA. (author)
  • Byler, Darrin D.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Durakiewicz, TomaszLos Alamos Natl Lab, Los Alamos, NM 87545 USA.;Marie Curie Sklodowska Univ, PL-20031 Lublin, Poland. (author)
  • Gilbertson, Steven M.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Kozimor, Stosh A.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Kvashnina, Kristina O.European Synchrotron ESRF, CS40220, F-38043 Grenoble 9, France.;Helmholtz Zentrum Dresden Rossendorf, Inst Resource Ecol, D-01314 Dresden, Germany. (author)
  • Nordlund, DennisSLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA. (author)
  • Rodriguez, GeorgeLos Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Seidler, Gerald T.Univ Washington, Seattle, WA 98195 USA. (author)
  • Bagus, Paul S.Univ North Texas, Denton, TX 76203 USA. (author)
  • Butorin, SergeiUppsala universitet,Molekyl- och kondenserade materiens fysik(Swepub:uu)sergbuto (author)
  • Conradson, Dylan R.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Espinosa-Faller, Francisco J.Univ Marista Merida, Merida 97300, Yucatan, Mexico. (author)
  • Hess, Nancy J.Pacific Northwest Natl Lab, Richland, WA 99352 USA. (author)
  • Kas, Joshua J.Univ Washington, Seattle, WA 98195 USA. (author)
  • Lezama-Pacheco, Juan S.Stanford Univ, Stanford, CA 94305 USA. (author)
  • Martin, PhilippeCEA, Nucl Energy Div, Res Dept Min & Fuel Recycling Proc, SFMA,LCC, F-30207 Bagnols Sur Ceze, France. (author)
  • Martucci, Mary B.Univ New Mexico, Los Alamos, NM 87544 USA. (author)
  • Rehr, John J.Univ Washington, Seattle, WA 98195 USA. (author)
  • Valdez, James A.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Bishop, Alan R.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Baldinozzi, GianguidoEcole Cent Paris, CNRS, F-99290 Chatenay Malabry, France. (author)
  • Clark, David L.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (author)
  • Tayal, AkhilSynchrotron Soleil, F-91192 Gif Sur Yvette, France. (author)
  • Inst Josef Stefan, Ljubljana 1000, Slovenia.;Washington State Univ, Pullman, WA 99164 USA.Los Alamos Natl Lab, Los Alamos, NM 87545 USA. (creator_code:org_t)

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  • In:Physical Review B96:122469-99502469-9969

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