The electronic structure of strongly correlated electrons at the surface of transition-metal oxides

本文采用局域密度近似（LDA）和动力学平均场理论（DMFT）的第一性原理方法研究了过渡金属氧化物表面强关联电子的电子结构。在DMFT计算中，单个安德森杂质问题采用Hirsch和Fye的量子Monte Carlo技术解决。本文主要研究了立方钙钛矿结构SrVO_3的（001）面，由于SrVO_3的表面结构未知，我们首先考虑了SrVO_3的理想解理面，即SrO层和VO_2层。我们使用FLAPW总能量代码（FLEUR）来确定表面原子在法向的弛豫。结果发现，构成八面体的O原子围绕中心V原子的位移相当小。对于所有的结构，我们使用嵌入式绿色函数方法确定半无限表面的LDA电子结构。对于<2g>SrO层封端表面，最外层V原子在法向的配位数减少导致d &lt;xz/yz&gt;带的LDA态密度显著变窄，从而导致表面准粒子谱的关联特征比体相更强.在VO 2-层终止表面的情况下，在最外面的V网站的局部八面体对称性的缺乏引起的V原子的价电子结构的实质性变化，并导致在一个相当大的重排的t_<2g>价电荷相比，散装。关联效应进一步促进了三个t轨道之间的电荷转移<2g>。

We have investigated the electronic structure of strongly correlated electrons at the surface of transition-metal oxides by a first principles method within the local density approximation (LDA) plus dynamical mean-field theory (DMFT). In the DMFT calculation, the single Anderson impurity problem was solved using the quantum Monte Carlo technique of Hirsch and Fye. We focused on the (001) surfaces of cubic perovskite SrVO_3 for which photoemission measurements were performed recently.As the surface structure of SrVO_3 is not known, we first considered its ideal cleaved surfaces with both SrO-layer and VO_2-layer terminations. We used the FLAPW total energy code (FLEUR) to determine the relaxations of surface atoms in the normal direction. It was found that the displacements of the O atoms that constitute octahedrons surrounding central V atoms are rather small. For all the structures, we determined the LDA electronic structure of semi-infinite surfaces using the embedded Green function method. Then, the calculated density of states (DOS) projected on the t_<2g> orbitals of an outermost V atom was used as an input to the subsequent DMFT calculations.For the SrO-layer terminated surfaces, the reduced coordination number of outermost V atoms in the normal direction gives rise to a significant narrowing of the LDA DOS for the d_<xz/yz> bands, which leads to stronger correlation features in the calculated surface quasi-particle spectra than in the bulk. In the case of VO2-layer terminated surfaces, the lack of the local octahedral symmetry at outermost V sites causes substantial changes in the valence electronic structure of the V atoms and results in a considerable rearrangement of t_<2g> valence charge compared to the bulk. This charge transfer among the three t_<2g> orbitals is further promoted by correlation effects.