OPTICAL CONDUCTIVITY OF COLOSSAL-MAGNETORESISTANCE COMPOUNDS : ROLE OF ORBITAL DEGENERACY IN THE FERROMAGNETIC PHASE
OPTICAL CONDUCTIVITY OF COLOSSAL-MAGNETORESISTANCE COMPOUNDS : ROLE OF ORBITAL DEGENERACY IN THE FERROMAGNETIC PHASE
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巨磁阻化合物的光学导电性：轨道简并在铁磁相中的作用
DOI：
10.1103/physrevb.59.6217
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发表时间：
1998
影响因子：
3.7
通讯作者：
F. Mack
中科院分区：
文献类型：
--
作者：
P. Horsch;J. Jaklic;F. Mack
最近的光学电导实验揭示了钙钛矿系统La_(1-x)Sr_xMnO_3的铁磁相谱分布的反常。利用有限温度对角化技术，我们研究了一个只包含$e_g$-轨道自由度的模型的$\sigma(\omega)$。由于强关联，轨道模型表现为具有各向异性相互作用和三位点跃迁的广义t-J模型。在轨道t-J模型中，σ(Omega)的特征是随温度降低而强度增加的宽非相干谱，以及一个重量较小的Drude峰，与实验相符。我们对两维体系的计算表明，轨道涨落的散射可以解释低温铁磁相中非相干部分的数量级。此外，我们还研究了轨道关联函数，结果表明：在低温下，掺杂平面模型中的轨道顺序为x^2~y^2。
Recent optical conductivity $\sigma(\omega)$ experiments have revealed an anomalous spectral distribution in the ferromagnetic phase of the perovskite system $La_{1-x}Sr_xMnO_3$. Using finite temperature diagonalization techniques we investigate $\sigma(\omega)$ for a model that contains only the $e_g$-orbital degrees of freedom. Due to strong correlations the orbital model appears as a generalized t-J model with anisotopic interactions and 3-site hopping. In the orbital t-J model $\sigma(\omega)$ is characterized by a broad incoherent spectrum with increasing intensity as temperature is lowered, and a Drude peak with small weight, consistent with experiment. Our calculations for two-dimensional systems, which may have some particular relevance for the double-layer manganites, show that the scattering from orbital fluctuations can explain the order of magnitude of the incoherent part of $\sigma(\omega)$ in the low temperature ferromagnetic phase. Moreover orbital correlation functions are studied and it is shown that $x^2$-$y^2$ orbital order is prefered in the doped planar model at low temperature.