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Title: Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x

Authors:
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Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1380058
Grant/Contract Number:
AC02-06CH11357; AC52-06NA25396; FG02-97ER45623; SC00008580; SC0016251
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 96; Journal Issue: 12; Related Information: CHORUS Timestamp: 2017-09-08 10:38:39; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society
Country of Publication:
United States
Language:
English

Citation Formats

Conradson, Steven D., Andersson, David A., Boland, Kevin S., Bradley, Joseph A., Byler, Darrin D., Durakiewicz, Tomasz, Gilbertson, Steven M., Kozimor, Stosh A., Kvashnina, Kristina O., Nordlund, Dennis, Rodriguez, George, Seidler, Gerald T., Bagus, Paul S., Butorin, Sergei M., Conradson, Dylan R., Espinosa-Faller, Francisco J., Hess, Nancy J., Kas, Joshua J., Lezama-Pacheco, Juan S., Martin, Philippe, Martucci, Mary B., Rehr, John J., Valdez, James A., Bishop, Alan R., Baldinozzi, Gianguido, Clark, David L., and Tayal, Akhil. Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x. United States: N. p., 2017. Web. doi:10.1103/PhysRevB.96.125114.
Conradson, Steven D., Andersson, David A., Boland, Kevin S., Bradley, Joseph A., Byler, Darrin D., Durakiewicz, Tomasz, Gilbertson, Steven M., Kozimor, Stosh A., Kvashnina, Kristina O., Nordlund, Dennis, Rodriguez, George, Seidler, Gerald T., Bagus, Paul S., Butorin, Sergei M., Conradson, Dylan R., Espinosa-Faller, Francisco J., Hess, Nancy J., Kas, Joshua J., Lezama-Pacheco, Juan S., Martin, Philippe, Martucci, Mary B., Rehr, John J., Valdez, James A., Bishop, Alan R., Baldinozzi, Gianguido, Clark, David L., & Tayal, Akhil. Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x. United States. doi:10.1103/PhysRevB.96.125114.
Conradson, Steven D., Andersson, David A., Boland, Kevin S., Bradley, Joseph A., Byler, Darrin D., Durakiewicz, Tomasz, Gilbertson, Steven M., Kozimor, Stosh A., Kvashnina, Kristina O., Nordlund, Dennis, Rodriguez, George, Seidler, Gerald T., Bagus, Paul S., Butorin, Sergei M., Conradson, Dylan R., Espinosa-Faller, Francisco J., Hess, Nancy J., Kas, Joshua J., Lezama-Pacheco, Juan S., Martin, Philippe, Martucci, Mary B., Rehr, John J., Valdez, James A., Bishop, Alan R., Baldinozzi, Gianguido, Clark, David L., and Tayal, Akhil. Fri . "Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x". United States. doi:10.1103/PhysRevB.96.125114.
@article{osti_1380058,
title = {Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in U O 2 + x},
author = {Conradson, Steven D. and Andersson, David A. and Boland, Kevin S. and Bradley, Joseph A. and Byler, Darrin D. and Durakiewicz, Tomasz and Gilbertson, Steven M. and Kozimor, Stosh A. and Kvashnina, Kristina O. and Nordlund, Dennis and Rodriguez, George and Seidler, Gerald T. and Bagus, Paul S. and Butorin, Sergei M. and Conradson, Dylan R. and Espinosa-Faller, Francisco J. and Hess, Nancy J. and Kas, Joshua J. and Lezama-Pacheco, Juan S. and Martin, Philippe and Martucci, Mary B. and Rehr, John J. and Valdez, James A. and Bishop, Alan R. and Baldinozzi, Gianguido and Clark, David L. and Tayal, Akhil},
abstractNote = {},
doi = {10.1103/PhysRevB.96.125114},
journal = {Physical Review B},
number = 12,
volume = 96,
place = {United States},
year = {Fri Sep 08 00:00:00 EDT 2017},
month = {Fri Sep 08 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on September 8, 2018
Publisher's Accepted Manuscript

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  • Mixed valence O-doped UO 2+x and photoexcited UO 2 containing transitory U 3+ and U 5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Fröhlich-type, nonequilibrium, phonon-coupled 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 UO 2, U 4O 9, and U 3O 7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f statesmore » of the valence band by ~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 UO 2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO 2 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 UO 2 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 UO 2 excited state. This heterogeneous, nonequilibrium, Fröhlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.« less
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  • The Ho2Ti2O7, Er2Ti2O7 and Yb2Ti2O7 pyrochlores were studied by synchrotron X-ray diffraction to determine whether the (002) peak, forbidden in the pyrochlore space group Fd-3m but observed in single crystal neutron scattering measurements, is present due to a deviation of their pyrochlore structure from Fd-3m symmetry. Synchrotron diffraction measurements on precisely synthesized stoichiometric and non-stoichiometric powders and a crushed floating zone crystal of Ho2Ti2O7 revealed that the (002) reflection is absent in all cases to a sensitivity of approximately one part in 30,000 of the strongest X-ray diffraction peak. This indicates to high sensitivity that the structural space group ofmore » these rare earth titanate pyrochlores is Fd-3m, and that thus the (002) peak observed in the neutron scattering experiments has a non-structural origin. The cell parameters and internal strain for lightly stuffed Ho2+xTi2-xO7 are also presented.« less
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