Magnetic quantum ratchet in graphene and ratchet effects in graphene with a lateral superlattice

棘轮效应描述了粒子在对称破缺的势中的周期性运动是如何在周期性激励下转化为定向运动的。在此，我们计划深入了解石墨烯棘轮效应的起源，并将其应用于石墨烯中的电子动力学研究。这将通过考虑两个模型系统来研究。首先，磁量子棘轮，其中垂直于石墨烯平面的对称性破缺、平面磁场和太赫兹辐射激发的共同作用导致直流电流，正如我们在最近的实验中所显示的那样。虽然这一现象在实验中得到了明确的证明，但人们还没有完全理解它。因此，我们计划详细研究石墨烯中磁量子棘轮效应的起源，并将其应用于研究该材料的对称性、各向异性和电子动力学。第二种模型系统是石墨烯与非对称周期性横向电位叠加，即破坏石墨烯平面的对称性。我们最近在石墨烯和具有一维横向电位的半导体异质结构中进行的太赫兹辐射诱导棘轮效应的实验表明，横向超晶格也会导致石墨烯中的棘轮效应。我们计划用周期调制系统地研究太赫兹辐射在石墨烯中诱导的棘轮效应，并开发这种效应的微观图像。我们的研究也为开发新型太赫兹辐射光电器件提供了科学依据。

Ratchet effects describe how the periodic motion of particles in a potential with broken symmetry, and subjected to periodic excitation, is converted to directed motion. Here we plan to get insight into the origin of ratchet effects in graphene and to apply them to study the electron dynamics in graphene. This will be studied by considering two model systems. First, the magnetic quantum ratchet, where the combined action of broken symmetry perpendicular to the graphene plane, an in plane magnetic field and excitation with terahertz radiation leads to a dc electric current, as we have shown in recent experiments. While this phenomenon is unambiguously demonstrated experimentally, it is not yet fully understood. We therefore plan to investigate in detail the origin of magnetic quantum ratchet effects in graphene and to apply them to study the symmetry, anisotropy and electron dynamics in this material. The second model system is graphene superimposed by a non-symmetric periodic lateral potential, i.e., breaking the symmetry in the graphene plane. Our recent experiments on THz radiation induced ratchet effect in graphene and semiconductor heterostructures with a one-dimensional lateral potential suggest that lateral superlattices should also lead to ratchet effects in graphene. We plan to investigate terahertz radiation induced ratchet effects in graphene with a periodic modulation systematically and to develop a microscopic picture of this effect. Our investigations should also provide a scientific basis for novel optoelectronic devices for THz radiation.