Controlling Valley Polarization in 2D Heterostructures

目前的电子信息处理装置是以控制电子电荷为基础的。然而，传统的电子器件架构正在达到基本的能量损失和小型化极限，这激发了对变革性纳米级器件的研究。一类原子薄的二维半导体中的电子提供电子谷自由度，可用于编码和潜在的信息处理。这些材料中的电子，特别是单层过渡金属二硫族化合物，可以占据两个不同的电子谷之一，这可以被理解为电子能带结构中可区分的口袋。因为有两个谷，它们可以用来将数字信息编码为1和0。重要的是，这些谷的激发产生中性粒子，其本质上比带电粒子产生更低的能量损失。在这个项目中，pi将开发光学和电子设备，目标是控制计算的谷自由度。他们将设计和制造新型电子设备，这些设备包括不同的超薄材料层，即无机和无机-有机混合设备，这将允许新的谷依赖功能。具体来说，他们将探索如何利用电子、磁和化学相互作用来设计携带谷信息的电荷中性电子态的空间输运。该项目的目标是了解如何控制电子谷信息并演示基于谷的逻辑门。该项目将通过展示如何在信息处理技术中使用谷来推进纳米技术领域。该项目开发了超小型光学和电子设备的新知识，培养了新一代科学家，实现了基本的小尺寸限制（原子薄），并有可能实现利用谷而不是电荷来编码信息的低能耗设备。本项目重点发展由二维异质结构组成的谷基器件。单层过渡金属二硫化物（TMD）半导体（即WSe2， MoSe2等）中的电子可以占据两个动量空间谷（+K和+K）中的一个，这可以用作二进制自由度来编码和潜在地处理信息。与自旋电子学类似，该项目旨在探索将利用谷极化控制应用于低能耗谷电子信息处理的设备架构。具体来说，将探索携带电荷中性层间激子并能够实现谷极化载流子微米尺度空间输运的异质结构。这些结构将发展成为基于非线性谷依赖相互作用效应的原型和变革性谷电子逻辑门，并依赖于光注入和读出。该项目有三个具体目标：1)控制具有层间激子和场效应结构的MoSe2/WSe2器件中的纯谷电流；2)利用界面交换相互作用控制铁磁/TMD异质结构中的谷极化和铁磁极化；3)在TMD/有机半导体异质结构中开发层间谷激子，以实现可调谐的层间激子系统、光学自旋注入和TMD谷简并的化学破缺。PI和co-PI将利用二维材料制造、有机半导体沉积和电子束光刻技术的组合来制造所提出的器件。TMD/TMD和铁磁/TMD器件将使用空间分辨微光致发光和非线性克尔光谱来探测激子能量和谷极化。TMD/有机异质结构将通过角分辨光发射和先进的x射线光谱进行表征。谷极化空间输运效应将被光学读出，并将通过在场效应异质结构器件中施加栅极电压、施加外部磁场和有机吸附剂图像化来控制。该项目将开发新型无机和混合有机/无机器件，这些器件有可能实现基于电子谷自由度的变革性技术。

Electronic information processing devices are currently based on controlling electron charge. However, traditional electronic device architectures are reaching fundamental energy loss and miniaturization limits, which motivate the investigation of transformative nanoscale devices. Electrons in a class of atomically thin two-dimensional semiconductors offer an electronic valley degree of freedom that can be used to encode and potentially process information. Electrons in these materials, specifically monolayer transition metal dichalcogenides, can occupy one of two different electronic valleys, which can be understood as distinguishable pockets in the electronic band structure. Because there are two valleys, they can be used to encode digital information as 1's and 0's. Importantly, excitation of these valleys creates neutral particle species that inherently incur lower energy losses than charged particles. In this project, the PIs will develop optical and electronic devices with the goal of controlling the valley degree of freedom for computing. They will design and fabricate novel electronic devices, which comprise disparate layers of ultra-thin materials, i.e. inorganic and hybrid inorganic-organic devices, which will allow for new valley dependent functionalities. Specifically, they will explore how electronic, magnetic and chemical interactions can be used to engineer spatial transport of charge neutral electronic states carrying valley information. The goal of the project is to understand how to control electronic valley information and to demonstrate valley-based logic gates. The project will advance the field of nanotechnology by demonstrating how valleys can be used in information processing technologies. The project develops new knowledge and trains a new generation of scientists in ultra-small optical and electronic devices that realize the fundamental small-sized limit (atomically thin), and could potentially enable low energy consumption devices that utilize valley instead of charge to encode information.This project focuses on the development of valley-based devices composed of two-dimensional heterostructures. Electrons in monolayer transition metal dichalcogenide (TMD) semiconductors (i.e. WSe2, MoSe2, etc.) can occupy one of two momentum space valleys (+K and +K), which can be used as a binary degree of freedom to encode and potentially process information. In analogy with spintronics, this project seeks to explore device architectures that will leverage the control of valley polarizations for applications to low energy consumption valleytronic information processing. Specifically, heterostructures that host charge-neutral interlayer excitons and can enable micron-scale spatial transport of valley polarized carriers will be explored. These structures will be developed into prototype and transformative valleytronic logic gates that are based on nonlinear valley-dependent interaction effects, and rely on optical injection and readout. The project has three specific aims: 1) controlling pure valley currents in MoSe2/WSe2 devices with interlayer excitons and field-effect structures; 2) controlling valley and ferromagnetic polarizations in ferromagnetic/TMD heterostructures using interfacial exchange-interactions; and 3) developing interlayer valley excitons in TMD/organic semiconductor heterostructures to enable a tunable interlayer exciton system, optical spin-injection, and chemically breaking of the TMD valley degeneracy. The PI and co-PI will utilize a combination of 2D material fabrication, organic semiconductor deposition and electron beam lithography techniques to fabricate the proposed devices. TMD/TMD and ferromagnetic/TMD devices will be investigated using spatially resolved micro-photoluminescence and nonlinear Kerr spectroscopies to probe the exciton energies and valley polarizations. The TMD/organic heterostructures will be characterized by angle-resolved photoemission and advanced x-ray spectroscopies. Valley polarized spatial transport effects will be read out optically, and will be controlled by applying gate voltages in field effect heterostructure devices, applying external magnetic fields, and patterning organic adsorbates. The project will develop novel inorganic and hybrid organic/inorganic devices that have potential to enable transformative technologies based on the electronic valley degree of freedom.