Electron-phonon coupling phenomena in low-dimensional and correlated materials

大量的现象产生于电子与一种叫做声子的物质的原子振动的相互作用。这些现象的例子包括电阻率、超导性和声子辅助光学吸收。目前的研究计划旨在使用第一性原理计算来研究这些现象，这种方法可以在没有任何可调参数的情况下提供材料的微观描述。通过各种项目，我们将采用新的方法来研究具有重要技术意义的材料中的电子-声子耦合。

A large number of phenomena arise from the interaction of electrons with the atomic vibrations of a materialscalled the phonons. Examples of these phenomena include the electric resistivity, superconductivity, and phonon-assisted optical absorption. The present research program aims to study these phenomena using first-principles calculations, an approach that provides a microscopic description of the materials without any adjustable parameters. Through the various projects, we will implement new methods to study electron-phonon coupling in materials of technological importance. The first subject of research will be the electrical conductivity in energy storage materials. We will study two-dimensional layered materials that can be used for the electrodes of supercapacitorsa type of fast-recharging batteries. For this project, we will implement a new algorithm to compute the phonon-limited electrical conductivity, which relies on a real-space interpolation of the phonon coupling potential. This work will accelerate the optimization of electrode materials for energy storage and offer efficient tools for further research on conducting nanomaterials. Another research direction is superconductivity in cuprates. The role of the electron-phonon interaction for the emergence of superconductivity in these materials is still a scientific debate, since previous calculations were not sufficiently accurate for these systems. We will employ novel algorithms based on many-body perturbation theory to capture the collective behavior of the electrons and compute the electron-phonon interaction strength with unmatched accuracy. The third research direction is the interplay between optical excitations and electron-phonon coupling. Phonon-assisted optical absorption explains the light absorption threshold in many materials, such as silicon. Yet, no method exists to fully describe this phenomenon. The difficulty is that two types of interactions need to be taken into account: the interaction of the electrons with the phonons, and the interaction of the electrons with the holes left after absorbing photons. We will implement a new theory that accounts for both types of interactions. It will allow us to understand the physics of phonon-assisted absorption and compute these phenomena from first principles. After the absorption of a photon in a materials, the optical excitationcalled an excitoncan move around and diffuse in another material. We will implement a new method to compute the scattering time of the excitons due to the phonon, which can be directly compared to experiments. It will allow us to study two-dimensional materials of technological importance, such as the transition metal dichalcogenides. This work will help the nanotechnology community understand how the microscopic design of optoelectronic devices affect their optical properties.