Neutron scattering investigation of the d - d excitations below the Mott gap of CoO
Neutron scattering investigation of the d - d excitations below the Mott gap of CoO
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CoO 莫特能隙以下 d - d 激发的中子散射研究
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
D. Prabhakaran
中科院分区：
文献类型：
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作者：
R. Cowley;W. Buyers;C. Stock;Z. Yamani;C. Frost;Jonathan W. Taylor;D. Prabhakaran
利用中子散射研究了CoO中Mott-Hubbard能隙下的单离子自旋和轨道激发。在0.870 $pm $0.009 eV，1.84 $pm $0.03和2.30 $pm $0.15 eV处报告了三个激发。这些参数化内的弱晶场计划与轨道内交换的$J（dd）$=1.3 $pm $0.2 eV和晶体场分裂10 Dq =0.94 $pm $0.10 eV。一个减少的自旋-轨道耦合的λ =-0.016 $pm $0.003 eV来自稀释样品的Mg$_{0.97}$Co$_{0.03}$O，测量，以消除并发症由于自旋交换和结构畸变参数分裂的立方相简并的轨道激发复杂的非弹性光谱。1.84 eV的电子伏特，虽然报告使用共振X射线和光学技术，是缺乏或弱的非共振X射线实验和重叠的预期位置的$^{4}A_{2}$的水平。这种过渡是不存在的偶极近似，但预计有一个有限的四极矩阵元素，可以观察到与中子散射技术在更大的动量转移。我们的研究结果同意与晶体场分析（在拉卡参数和Tanabe-Sugano图），并与以前的计算使用局部密度带理论莫特绝缘过渡金属氧化物。结果还表明，使用中子散射测量偶极禁戒过渡金属氧化物系统的转变。
Neutron scattering is used to investigate the single-ion spin and orbital excitations below the Mott-Hubbard gap in CoO. Three excitations are reported at 0.870 $pm$ 0.009 eV, 1.84 $pm$ 0.03, and 2.30 $pm$ 0.15 eV. These were parameterized within a weak crystal field scheme with an intra-orbital exchange of $J(dd)$=1.3 $pm$ 0.2 eV and a crystal field splitting 10Dq=0.94 $pm$ 0.10 eV. A reduced spin-orbit coupling of lambda=-0.016 $pm$ 0.003 eV is derived from dilute samples of Mg$_{0.97}$Co$_{0.03}$O, measured to remove complications due to spin exchange and structural distortion parameters which split the cubic phase degeneracy of the orbital excitations complicating the inelastic spectrum. The 1.84 eV, while reported using resonant x-ray and optical techniques, was absent or weak for non resonant x-ray experiments and overlaps with the expected position of a $^{4}A_{2}$ level. This transition is absent in the dipolar approximation but expected to have a finite quadrupolar matrix element that can be observed with neutron scattering techniques at larger momentum transfers. Our results agree with a crystal field analysis (in terms of Racah parameters and Tanabe-Sugano diagrams) and with previous calculations performed using local-density band theory for Mott insulating transition metal oxides. The results also demonstrate the use of neutron scattering for measuring dipole forbidden transitions in transition metal oxide systems.