铁磁YTiO_3光学响应的椭圆偏振光谱研究
Optical response of ferromagnetic YTiO_3 studied by spectral ellipsometry
摘要：
本文研究了电绝缘、近化学计量比、铁磁居里温度T_C = 30 K的YTiO_3单晶的椭偏光谱随温度的变化。光学响应表现出弱但明显的各向异性。使用一个经典的色散分析，我们确定了三个低能量的光学波段在2.0，2.9，和3.7 eV。虽然在300 K以下的光导谱仅弱地依赖于温度，但我们能够区分高温和低温区域，在100 K附近具有明显的交叉点。在光学响应的低温制度与居里-外斯平均场行为的显着偏差，在磁化中观察到的温度范围相吻合。使用基于简单超交换模型的分析，光谱权重重排可以归因于位间d_i^1d_j^1 \longrightarrow d_i^2d_j^0光学跃迁。特别地，在2.9 eV附近的光谱中的Kramers-Kronig一致变化可以与高自旋态（^3T_1）光学跃迁相关联。这表明，其他机制，如弱偶极允许的p-d跃迁和/或激子-极化子激发，可以显着贡献的光学带在2 eV。在2.9 eV的光学波段记录的光谱增重被显著抑制和各向异性，我们认为这与复杂的自旋-轨道-晶格现象在铁磁有序温度附近的YTiO 3。
英文摘要：
We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO_3 single crystal with ferromagnetic Curie temperature T_C = 30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV. Although the optical conductivity spectra are only weakly temperature dependent below 300 K, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around 100 K. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from Curie-Weiss mean field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite d_i^1d_j^1 \longrightarrow d_i^2d_j^0 optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around 2.9 eV can be associated with the high-spin-state (^3T_1) optical transition. This indicates that other mechanisms, such as weakly dipole-allowed p-d transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at 2 eV. The recorded optical spectral weight gain of 2.9 eV optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near ferromagnetic ordering temperature in YTiO_3.
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