Orbital, spin and charge fluctuations in layered oxide heterostructures

该项目的目标是通过能带结构计算以及动态平均场理论及其扩展的定制实现来研究过渡金属氧化物的层状异质结构。对这些新材料的理论理解，现在可以以可控的方式生长，不仅有利于界面电子特性的基础研究，而且有利于技术开发和器件制造。特别是，从头算研究是特别及时的，因为A。Ohtomo和H. Hwang [Nature 419，378（2002）]认为，带-（即，标准）绝缘体如SrTiO 3和Mott-（即，强相关的）绝缘体如LaTiO 3可以导电，还没有完全令人满意的理论解释。此外，包含具有部分填充的d-壳层的其他材料的新异质结构目前处于聚光灯下（例如，LaVO3/SrTiO 3）。这就增加了对远离常规体积极限的系统中的电子相关效应的理解的需要。有许多问题需要回答，如交替的正LaO和负TiO 2层是否会在LaTiO 3部分产生非零电位梯度，以及在多大程度上这与临界LaTiO 3厚度的存在有关，在该临界LaTiO 3厚度以上界面变为金属。此外，它是非常重要的，以评估是否可以在相同的理论框架内描述LaVO 3/SrTiO 3和什么样的轨道特性的移动的载流子在界面处。密度泛函理论的计算和动态平均场理论的新实现，专门设计用于处理不等价层，可以可靠地考虑，一方面，电子结构，另一方面，强电子相关的影响。因此，我们的研究可以澄清一些悬而未决的问题，并刺激具有不同功能的新的异质结构的合成。

The goal of this project is to investigate layered heterostructures of transition-metal oxides by means of band-structure calculations as well as tailor-made implementations of Dynamical Mean Field Theory and its extensions. A theoretical understanding of these novel materials, which can nowadays be grown in a controlled way, is going to benefit not only basic research on electronic properties at interfaces but also technological development and device fabrication. In particular, an ab-initio study is particularly timely, as the stunning discovery by A. Ohtomo and H. Hwang [Nature 419, 378 (2002)] that the interface between a band- (i.e., standard) insulator like SrTiO3 and a Mott- (i.e., strongly-correlated) insulator like LaTiO3 can be conducting has not yet been followed by a fully satisfactory theoretical explanation. In addition, new heterostructures containing other materials with partially filled d-shells are currently in the spotlight (e.g., LaVO3/SrTiO3). This increases the need of an understanding of electronic correlation effects in systems that are far from the conventional bulk limit. There are many questions that need to be answered, such as whether or not alternating positive LaO and negative TiO2 layers give rise to a nonzero potential gradient in the LaTiO3 part and also to what extent this is related to the existence of a critical LaTiO3 thickness above which the interface becomes metallic. Furthermore, it is very important to assess if one can describe within the same theoretical framework LaVO3/SrTiO3 and what the orbital character of the mobile carriers at the interface is. Density Functional Theory calculations and new implementations of Dynamical Mean Field Theory specifically designed to treat inequivalent layers can reliably take into account, on the one hand, the electronic structure and, on the other, the effects of strong electronic correlation. Our study can therefore clarify some of the open questions and stimulate the synthesis of new heterostructures with distinct functionalities.