权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Giant magneto-photoelectric effect in graphene

石墨烯中的巨磁光电效应

基本信息

批准号：
398912239
负责人：
Dr. Friedemann Queisser
金额：
--
依托单位：
Institut für Theoretische Physik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2018
资助国家：
德国
起止时间：
2017-12-31 至 2022-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/398912239?language=en
关键词：
Giant magneto photoelectric effect graphene

项目摘要

The efficiency of solar cells is bounded by the so-called Shockley-Queisser-limit. Within this research project, we want to propose an alternative setting which converts radiation into electric energy an might be able to overcome this limit. In particular, we want to study the current generation in a graphene fold (or a graphene flake with boundary) which is subject to a constant magnetic field: Electrons and holes move in opposite directions such that reflections at the graphene fold (graphene boundary) separate the charges and generate a current along the fold (boundary). Since the mean free path in graphene is on the micrometer scale whereas the typical cyclotron radius for an electron (for an energy in the meV range and a magnetic field of a few Tesla) is in the nanometer range, the charge separation is only slightly disturbed by scattering events.The band structure of graphene has no energy gap, therefore also long-wave photons can be absorbed.Due to these reasons, it might be feasible that the efficiency of the proposed setting exceeds the efficiency of commercially available solar cells. Indeed, a first experimental realization showed that 100 incoming photons generate up to 17 particle-hole pairs which is in contradiction to graphene's absorption probability of 2.3%. A possible origin of the observed giant-magnetophotoelectric effect is the generation of secondary particle-hole pairs at the graphene fold (edge) via Coulomb scattering.The first part of this proposal concerns the absorption probability of a graphene fold (a graphene boundary) within the single-particle picture.Using the continuum description of electrons in graphene we shall investigate its dependenceon the value of the magnetic field, the value of the chemical potential and external electric fields. Using these findings, we will investigate the secondary particle-hole pair creation. As a first step, we shall employ Fermi's golden rule to estimate qualitatively the probabilities of the scattering processes.Since the dimensionless parameter of the perturbation expansion(the effective fine-structure constant in graphene) is about 300 times larger than the fine-structure constant of quantum electrodynamics,we will apply two non-perturbative methods in order to obtain quantitative estimates.The first method is based on the continued fraction representation of solutions of the many-particle Lippmann-Schwinger-equation.Owing to the non-polynomial nature of this approximation scheme, we expect a better convergence compared to a polynomial perturbation theory.The second method is based on a hierarchy of correlation functions. In a further subproject, we shall investigate the impact of the boundary shape on the current generation.

太阳能电池的效率受到所谓的肖克利-奎瑟极限的限制。在这项研究项目中，我们希望提出一种将辐射转化为电能的替代设置，并可能能够克服这一限制。特别是，我们想要研究受恒定磁场影响的石墨烯折叠(或有边界的石墨烯薄片)中的电流产生：电子和空穴以相反的方向运动，使得在石墨烯折叠(石墨烯边界)处的反射分离电荷，并沿折叠(边界)产生电流。由于石墨烯的平均自由程在微米尺度上，而电子的典型回旋半径(能量在MeV范围内，磁场为几特斯拉)在纳米范围内，电荷分离仅受到散射事件的轻微干扰。石墨烯的能带结构没有能隙，因此也可以吸收长波光子。由于这些原因，所提出的设置的效率可能超过商业太阳能电池的效率。事实上，第一个实验实现表明，100个入射光子产生多达17个粒子-空穴对，这与石墨烯2.3%的吸收几率相反。观察到的巨磁光电效应的一个可能的来源是通过库仑散射在石墨烯折叠(边缘)处产生二次粒子-空穴对。这一建议的第一部分涉及单粒子图像中石墨烯折叠(石墨烯边界)的吸收几率。利用石墨烯中电子的连续描述，我们将研究它与磁场、化学势和外部电场的值的关系。利用这些发现，我们将研究二次粒子-空穴对的产生。作为第一步，我们将使用费米黄金法则来定性地估计散射过程的概率。由于微扰展开的无量纲参数(石墨烯中的有效精细结构常数)大约是量子电动力学精细结构常数的300倍，我们将应用两种非微扰方法来获得定量估计。第一种方法基于多粒子Lippmann-Schwinger方程解的连分式表示。由于这种近似方案的非多项式性质，我们期望比多项式微扰理论有更好的收敛。第二种方法是基于关联函数族。在下一个子项目中，我们将调查边界形状对当前世代的影响。