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Charge density distribution and optical response of the LaAlO_3/SrTiO_3 interface

机译：LaAlO_3 / SrTiO_3界面的电荷密度分布和光学响应

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摘要

We present calculations of the charge density profile, subband occupancy, and ellipsometry spectra of the electron gas at the LaAlO_3/SrTiO_3 interface. The calculations employ self-consistent Hartree and random phase approximations, a tight-binding parametrization of the band structure, and a model for the optical phonon of SrTiO_3. The dependence of the spatial structure and occupancy of subbands on the magnitude of the polarization charge at the interface and the dielectric function is determined. The interface-confined subbands may be labeled by the symmetry (xy, xz, or yz) of the Ti d orbitals from which they mainly derive. The xy-derived band nearest the interface contains the major proportion of the electronic charge, but a large number of more distant, slightly occupied xy-derived bands are also found. Depending on the magnitude of the polarization charge, zero, one, or two xz/yz-derived subbands are found. When present, these xz/yz bands give the dominant contribution to the long-distance tail of the interface charge. The response to applied ac electric fields polarized parallel and perpendicular to the interface is calculated and the results are presented in terms of ellipsometry angles. Two features are found: a dip in the spectrum near the longitudinal optic (LO) feature of the SrTiO_3 phonon and a peak at the higher energy. We show that the form and magnitude of the dip are related to the Drude response of carriers moving in the plane of the interface, while the peak arises from the plasmon excitation of the xz and yz electrons. The relation of the features of the subband occupancies and the in-plane conductivities is given.
机译：我们介绍了在LaAlO_3 / SrTiO_3界面上电子气的电荷密度分布，子带占有率和椭偏光谱的计算。计算采用自洽的Hartree和随机相位近似，能带结构的紧密绑定参数化以及SrTiO_3光学声子模型。确定了子带的空间结构和占用率对界面处极化电荷的大小和介电函数的依赖性。受限于界面的子带可以通过其主要来源的Ti d轨道的对称性（xy，xz或yz）进行标记。最靠近界面的xy衍生带包含了大部分的电荷，但也发现了大量更远，略占的xy衍生带。根据极化电荷的大小，可以找到零个，一个或两个xz / yz派生的子带。当存在时，这些xz / yz带对界面电荷的长距离尾部起主要作用。计算对平行和垂直于界面极化的施加的交流电场的响应，并以椭圆偏振角表示结果。发现了两个特征：SrTiO_3声子的纵向光学（LO）特征附近的光谱下降和较高能量处的峰。我们表明，倾角的形式和幅度与在界面平面内移动的载流子的Drude响应有关，而峰值则来自xz和yz电子的等离子体激元激发。给出了子带占用率特征与平面内电导率的关系。

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