论文标题
srtio $ _3 $（001）上的lacoo $ _ {3} $的缺陷订购和现场不成比例的竞争
Competition of defect ordering and site disproportionation in strained LaCoO$_{3}$ on SrTiO$_3$(001)
论文作者
论文摘要
$ 3 \ times 1 $重建的起源是在Srtio $ _3（001）$上的外观上lacoo $ _ {3} $胶片中观察到的，该$是通过使用包括库仑排斥项在内的第一原则计算来评估的。我们将相图作为氧气压力编译，这表明（$ 3 \ times 1 $） - 有序的氧空位（Lacoo $ _ {2.67} $）在常用的生长条件下受到青睐，而在氧气富含氧气的条件下，stoichiemetric emmetric emmetric films Emerge Emerge Emerge。进一步减少的lacoo $ _ {2.5} $ brownmillerite膜受到相位分离的阻碍。我们报告了两种竞争化学计量膜的竞争地基候选者：一个半金属相，$ 3 \ times 1 $低旋转/中间自旋/中间旋转磁序，以及具有中间旋转磁性顺序的半导体阶段。这表明，即使在没有氧气空位的情况下，拉伸菌株也会诱导铁磁性。这两个阶段均表现出有趣的（$ 3 \ times 1 $） - 重建的八面体旋转模式，并因此调制了La-la距离。特别是，在CO地点出现了$ t_ {2g} $孔的电荷和债券含量和伴随轨道顺序，这些孔在中间旋转状态下也观察到了未经培训的散装lacoo $ _3 $，并解释了在高度温度下通过X射线差异获得的结构数据。位点不成比例驱动了金属到肺导体的转变，该转变将中间旋转状态与实验观察到的旋转状态跨界时的电导率低，而无需Jahn-Teller畸变。
The origin of the $3 \times 1$ reconstruction observed in epitaxial LaCoO$_{3}$ films on SrTiO$_3(001)$ is assessed by using first-principles calculations including a Coulomb repulsion term. We compile a phase diagram as a function of the oxygen pressure, which shows that ($3 \times 1$)-ordered oxygen vacancies (LaCoO$_{2.67}$) are favored under commonly used growth conditions, while stoichiometric films emerge under oxygen-rich conditions. Growth of further reduced LaCoO$_{2.5}$ brownmillerite films is impeded by phase separation. We report two competing ground-state candidates for stoichiometric films: a semimetallic phase with $3 \times 1$ low-spin/intermediate-spin/intermediate-spin magnetic order and a semiconducting phase with intermediate-spin magnetic order. This demonstrates that tensile strain induces ferromagnetism even in the absence of oxygen vacancies. Both phases exhibit an intriguing ($3 \times 1$)-reconstructed octahedral rotation pattern and accordingly modulated La-La distances. In particular, charge and bond disproportionation and concomitant orbital order of the $t_{2g}$ hole emerge at the Co sites that are also observed for unstrained bulk LaCoO$_3$ in the intermediate-spin state and explain structural data obtained by x-ray diffraction at elevated temperature. Site disproportionation drives a metal-to-semiconductor transition that reconciles the intermediate-spin state with the experimentally observed low conductivity during spin-state crossover without Jahn-Teller distortions.
