Mesoscopic current patterns and orbital magnetism induced by dc-voltages

• Applicant: Professor Dr. Ferdinand Evers
• Subject Area: Theoretical Condensed Matter Physics ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257888954

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.

• DFG Programme: Research Grants
• International Connection: USA
• Participating Person: Professor Charles Stafford, Ph.D.