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。研究的第一个课题将是储能材料的导电性。我们将研究可用于超级电容器（一种快速充电电池）电极的二维分层材料。在这个项目中，我们将实现一种新的算法来计算声子限制电导率，该算法依赖于声子耦合势的实空间插值。这项工作将加速能量存储电极材料的优化，并为进一步研究导电纳米材料提供有效的工具。另一个研究方向是铜酸盐的超导性。电子-声子相互作用在这些材料中出现超导性的作用仍然是一个科学争论，因为以前的计算对这些系统不够精确。我们将采用基于多体摄动理论的新算法来捕捉电子的集体行为，并以无与伦比的精度计算电子-声子相互作用强度。第三个研究方向是光激发与电子-声子耦合的相互作用。声子辅助光学吸收解释了许多材料（如硅）的光吸收阈值。然而，没有一种方法可以完全描述这种现象。困难在于需要考虑两种类型的相互作用：电子与声子的相互作用，以及电子与吸收光子后留下的空穴的相互作用。我们将实现一个新的理论来解释这两种类型的相互作用。它将使我们能够理解声子辅助吸收的物理学，并从第一性原理计算这些现象。在一种材料吸收光子后，光激发——称为激子——可以在另一种材料中四处移动和扩散。我们将实现一种新的方法来计算由声子引起的激子散射时间，这可以直接与实验进行比较。它将使我们能够研究具有重要技术意义的二维材料，如过渡金属二硫族化合物。这项工作将有助于纳米技术社区了解光电器件的微观设计如何影响其光学特性。

A large number of phenomena arise from the interaction of electrons with the atomic vibrations of a materials-called 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 supercapacitors-a 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 excitation-called an exciton-can 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.