Mesoscopic current patterns and orbital magnetism induced by dc-voltages

纳米科学的很大一部分是关于电荷密度对外加电场的响应。在这个项目中，我们在原子尺度上分析了这种电荷响应的局部空间结构。我们的准备工作使用了我们自制的从头算传输模拟包AITRANSS。该软件包允许计算复杂的电流模式在功能化有机材料，如石墨烯片与氢吸附剂。这些电流模式表现出令人惊讶和强烈的特征，例如局部环电流的幅度可以超过平均输运电流一个数量级。为了在从头算水平上更系统地研究这种效应，需要以自一致的方式考虑感应电场和磁场对电流的影响。因此，应该开发一种采用当前密度泛函理论（CDFT）的输运形式。这就是我们在这个项目中要做的：在它的主要研究路线中，CDFT将在我们的包AITRANSS中实现。为了便于第一次定量估计，我们将忽略对Kohn-Sham规范电位的交换相关校正。这相当于包括电流诱导的洛伦兹力，但忽略了通过相互作用效应的（非平衡）重整化。我们设想这种新颖的、基于cdft的输运形式在表面科学和介观物理的几个子领域的富有成效的应用。首先，我们将研究电流诱导的洛伦兹力是否可以变得足够大，以便它们可以用于分子磁体的可控开关。其次，我们将研究流线和涡流在介观样品中产生热量的作用。第三，我们想研究感应磁场的统计性质，例如，为了预测当前模式的局部性质如何进入全局（粗粒度）可观测值。第四，研究非常规材料（如拓扑物质）中的局部电流模式是非常有趣的。事实上，拓扑绝缘体表现出反常的介电响应，一种量子化的双各向异性，这也应该在局部电流模式中表现出来。最后，我们提到，本建议中所作的技术发展也应与材料科学相关。也就是说，我们在这里提出计算的（时间相关的）电场的磁响应也会产生那些最近在光子学和超材料领域被认为非常重要的双各向异性。我们的研究有助于从从头开始计算这种双各向异性铺平道路。

A very large part of the nano-sciences is concerned with the response of the charge density to externally applied electric fields. In this project we analyze the local spatial structure of this charge response on the atomistic scale. Our preparative work employs our homemade ab-initio transport simulation package AITRANSS. The package allows to calculate complicated current patterns in functionalized organic materials, such as graphene flakes with hydrogen adsorbants. These current patterns exhibit surprising and strong features such as local ring currents with an amplitude that can exceed the average transport current by an order of magnitude. In order to investigate such effects more systematically on an ab-initio level, one needs to take the effect of the induced electric and magnetic fields on the current flow into account in a self-consistent manner. Thus, a transport formalism should be developed that employs the current density functional theory (CDFT). This is what we propose to do in this project: In its main research line the CDFT is to be implemented in our package AITRANSS. To fascilitate a first quantitative estimate we will ignore exchange-correlation corrections to the Kohn-Sham gauge potential. This amounts to including current-induced Lorentz-forces but neglecting (non-equilibrium) renormalizations through interaction-effects. We envision fruitful applications of this novel, CDFT-based transport formalism in several subfields of surface sciences and mesoscopic physics. First, we will investigate whether the current induced Lorentz forces can become sufficiently sizable so that they may be used for controllable switching of molecular magnets. Second, we will investigate the role of streamlines and eddies for the heat generation in the mesoscopic sample. Third, we would like to study the statistical properties of induced magnetic fields, for instance, in order to predict how the local properties of current patterns enter global (coarse-graining) observables. Forth, it is highly interesting to investigate local current patterns in unconventional materials, such as topological matter. In fact, topological insulators exhibit an anomalous dielectric response, a quantized bianisotropy, that should manifest itself also in local current patterns. Finally, we mention that the technological developments made in this proposal should be relevant also in the materials sciences. Namely, the magnetic response to (time dependent) electric fields, which we propose to calculate here, also gives rise to those bianisotropies that have recently been recognized as very important in the field of photonics and meta-materials. Our research can help paving the way for the calculation of such bianisotropies from ab-initio.