...
首页> 外文期刊>Physical review >Possible Bose-condensate behavior in a quantum phase originating in a collective excitation in the chemically and optically doped Mott-Hubbard system UO_(2+x)
【24h】

Possible Bose-condensate behavior in a quantum phase originating in a collective excitation in the chemically and optically doped Mott-Hubbard system UO_(2+x)

机译:在化学和光学掺杂的Mott-Hubbard系统UO_(2 + x)中的集体激发引起的量子相中可能的玻色凝聚行为

获取原文
获取原文并翻译 | 示例
           

摘要

X-ray pair distribution function (pdf) and U L_3 extended x-ray absorption fine structure (EXAFS) and neutron pdf measurements that give identical results for UO_2 show U(VI)-oxo moieties with x rays for mixed valence U_4O_9 and U_3O_7, in contrast to the neutron data that indicate only U(V) sites with no short U-O bonds as well as other differences. In addition, although the EXAFS spectra of UO_2 are essentially identical at 30,100, and 200 K, those of the UO_(2+x) compounds exhibit different nearest-neighbor U-O distributions at each temperature. Further tunneling polaron-type behavior is found in the broadening of the features of the O K-edge x-ray absorption spectra (XAS) of the UO_(2+x) compounds. Raman spectra of powders also show a large increase in scattering cross section with increasing O content that would originate in a change in the electronic structure that increases the overall polarizability. The XAS and Raman also show that U_4O_9 does not behave as a linear combination of the UO_2 and U_3O_7 fluorite endpoints. The properties induced by mobile rather than static charged quasiparticles were explored by optical pumping of the metal-to-metal charge-transfer transition. The temperature dependence of 4.71 eV pump-1.57 eV probe reflectivity on UO_2 that initially populates the U 6d-dominated portion of the upper Hubbard band (UHB) shows a sharp 28-μsec lifetime peak at 25 K that may be associated with the fluctuations of its antiferromagnetic transition. Pumping at 3.14 eV into the 5ƒ-dominated portion of the UHB shows an analogous 2.8-μsec peak but also a plateau bracketing this peak that ends in a cusp at 50-60 K and an abrupt change in the hardening rate of a novel 12-15 GHz phonon that is the signature for the quasiparticle quantum phase. The different results for the different excitation channels indicate a highly specific nonthermal relaxation mechanism. These results constitute the first observation of a distinct phase of photoinduced quasiparticles that is sufficiently coupled to the lattice to undergo a gap-opening transition. When the intragap state is probed with a terahertz time domain spectroscopy (TTDS) measurement 33 psec after a 3.14 excitation pulse, it shows increased absorption in the 0.5-1.1 THz range with a decrease in temperature from ~30 to 10 K instead of the expected decrease, a result consistent with the presence of a condensate. These results are too extreme to originate in the dynamical, nonadiabatic, coupled charge-transfer-phonon/tunneling polaron scenario previously used for doped Mott-Hubbard insulators with intermediate electron-phonon coupling and therefore indicate novel physics. One possibility that could cause all of these behaviors is that a collective, dynamical, charge transfer-coupled Peierls distortion involving the 2 U(Ⅴ) ↔ U(Ⅳ) + U(Ⅵ)-oxo excitation occurs coherently over an entire domain to cause the atoms in this domain to condense into a system with Bose-Einstein or Bose-Einstein-Hubbard properties.
机译:X射线对分布函数(pdf)和U L_3扩展的X射线吸收精细结构(EXAFS)和中子pdf测量得出与UO_2相同的结果,显示X价为U_4O_9和U_3O_7的具有X射线的U(VI)-氧代部分,与中子数据相反,中子数据仅显示没有短UO键以及其他差异的U(V)位。此外,尽管UO_2的EXAFS光谱在30,100和200 K时基本相同,但UO_(2 + x)化合物的EXAFS光谱在每个温度下均表现出不同的近邻U-O分布。在扩大UO_(2 + x)化合物的O K边缘x射线吸收光谱(XAS)的特征时,发现了进一步的隧穿极化子型行为。粉末的拉曼光谱还显示,随着O含量的增加,散射截面会大大增加,这将源于电子结构的变化,从而增加了整体极化率。 XAS和拉曼光谱还表明,U_4O_9不能作为UO_2和U_3O_7萤石终点的线性组合。通过光泵浦金属到金属的电荷转移跃迁,探索了由可移动而不是带静电荷的准粒子诱发的特性。最初在上哈伯德带(UHB)的U 6d占主导地位的部分的UO_2上的4.71 eV泵-1.57 eV探针反射率的温度依赖性显示在25 K时存在28μs的尖锐寿命峰值,这可能与它的反铁磁跃迁。在3.14 eV下泵入UHB的5ƒ主导部分时,显示出一个类似的2.8μsec峰值,但也出现了一个平台,将这个峰值括起来,最终在50-60 K处达到尖峰,并且新型12-N的硬化速率突然改变。 15 GHz声子,是准粒子量子相的特征。不同激发通道的不同结果表明高度特定的非热弛豫机制。这些结果构成了对光致准粒子的不同相的首次观察,该相充分耦合到晶格以进行间隙开放跃迁。在3.14激发脉冲后33 ps内用太赫兹时域光谱(TTDS)测量探测间隙内状态时,它显示出在0.5-1.1 THz范围内的吸收增加,温度从〜30降低到10 K,而不是预期的减少,这与冷凝物的存在一致。这些结果太极端了,无法起源于以前用于具有中间电子-声子耦合的掺杂Mott-Hubbard绝缘子的动态,非绝热,耦合的电荷转移-声子/隧道极化子情形,因此表明了新的物理学。可能导致所有这些行为的一种可能性是,涉及2 U(Ⅴ)↔U(Ⅳ)+ U(Ⅵ)-氧代激发的集体的,动态的,电荷转移耦合的Peierls畸变在整个域内相干发生,从而引起该域中的原子凝聚成具有Bose-Einstein或Bose-Einstein-Hubbard特性的系统。

著录项

  • 来源
    《Physical review》 |2013年第11期|115135.1-115135.21|共21页
  • 作者单位

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Universidad Marista de Merida, Merida, Yucatan 97300, Mexico;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA SUNY Albany, Albany, New York 12222, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA University of Washington, Seattle, Washington 98195, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Pacific Northwest National Laboratory, Richland, Washington 99352, USA;

    Institute for Transuranium Elements, Karlsruhe, 76344, Germany;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Cinvestav-Merida, Merida, Yucatan, 97310, Mexico;

    SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Stanford University, Stanford, California 94305, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    University of Washington, Seattle, Washington 98195, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

    New Jersey Institute of Technology, Newark, New Jersey 07102, USA;

    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA;

  • 收录信息
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号