[论文解读] All-Electrical Spin Field Effect Transistor in van der Waals Heterostructures at Room Temperature

André Dankert, Saroj P. Dash|arXiv (Cornell University)|Oct 20, 2016

Quantum and electron transport phenomena参考文献 29被引用 7

一句话总结

该论文首次在室温下实现了基于范德华异质结的全电控自旋场效应晶体管（自旋-FET），采用石墨烯/MoS₂异质结，通过调控肖特基势垒和MoS₂电导率，实现栅压可调的自旋极化与自旋寿命。关键成果是在环境条件下实现了石墨烯中电控自旋输运与Hanle进动信号，实现了自旋电子器件中全电控自旋操作。

ABSTRACT

Spintronics aims to exploit the spin degree of freedom in solid state devices for data storage and information processing technologies. The fundamental spintronic device concepts such as creation, manipulation and detection of spin polarization has been demonstrated in semiconductors and spin transistor structures using both the electrical and optical methods. However, an unsolved challenge in the field is the realization of all electrical methods to control the spin polarization and spin transistor operation at ambient temperature. For this purpose, two-dimensional (2D) crystals offer a unique platform due to their remarkable and contrasting spintronic properties, such as weak spin-orbit coupling (SOC) in graphene and strong SOC in molybdenum disulfide (MoS$_2$). Here we combine graphene and MoS$_2$ in a van der Waals heterostructure to realize the electric control of the spin polarization and spin lifetime, and demonstrated a spin field-effect transistor (spin-FET) at room temperature in a non-local measurement geometry. We observe electrical gate control of the spin valve signal due to pure spin transport and Hanle spin precession signals in the graphene channel in proximity with MoS$_2$ at room temperature. We show that this unprecedented control over the spin polarization and lifetime stems from the gate-tuning of the Schottky barrier at the MoS$_2$/graphene interface and MoS$_2$ channel conductivity leading to spin interaction with high SOC material. The all-electrical creation, transport and control of the spin polarization in a spin-FET device at room temperature is a substantial step in the field of spintronics. It opens a new platform for the interplay of spin, charge and orbital degrees of freedom for testing a plethora of exotic physical phenomena, which can be key building blocks in future device architectures.

研究动机与目标

• 在室温下实现自旋电子器件中自旋极化与自旋寿命的全电控。
• 克服传统半导体异质结在室温下运行自旋-FET所面临的长期挑战。
• 利用二维材料的对比自旋电子特性——石墨烯中弱自旋-轨道耦合与MoS₂中强自旋-轨道耦合——实现增强的自旋控制。
• 在非局部几何结构中展示功能性自旋-FET，采用纯自旋输运与Hanle进动测量。

提出的方法

• 通过机械剥离与干法转移技术制备范德华异质结，材料为石墨烯与二硫化钼（MoS₂）。
• 将异质结集成至非局部自旋阀结构中，配备顶栅电介质与栅电极，实现电控。
• 施加栅压以调节MoS₂/石墨烯界面处的肖特基势垒，并调制MoS₂沟道电导率。
• 通过非局部电压探测测量自旋输运，并利用Hanle进动信号探测自旋极化与自旋寿命。
• 利用电学栅控实现自旋极化的电控生成、传输与探测，无需外加磁场。
• 分析栅压依赖的自旋阀与Hanle信号，确认自旋寿命与极化的可调性。

实验结果

研究问题

• RQ1 能否在室温下，利用二维范德华异质结，实现自旋-FET中自旋极化与自旋寿命的全电控？
• RQ2 在电学栅控下，MoS₂/石墨烯界面处的肖特基势垒如何影响自旋输运与自旋寿命？
• RQ3 栅压在多大程度上可通过与MoS₂等强自旋-轨道耦合材料的相互作用，调制石墨烯中的自旋寿命？
• RQ4 在室温下，石墨烯沟道与MoS₂耦合时，能否观测到纯自旋输运与Hanle进动？
• RQ5 自旋极化是否可仅通过电学手段实现控制，而无需光学激发或外加磁场？

主要发现

• 作者在室温下展示了石墨烯沟道中栅压可调的自旋阀信号，证实了自旋注入与输运的电控能力。
• 在非局部结构中清晰观测到Hanle进动信号，表明石墨烯中自旋在微米尺度距离内实现了相干输运。
• 通过栅压实现了石墨烯中自旋寿命的电控调制，其变化归因于肖特基势垒与MoS₂电导率的调控。
• 自旋极化完全通过电学手段实现控制，无需外加磁场或光学激发。
• 观测到的自旋输运与控制源于石墨烯的长自旋扩散长度与MoS₂的强自旋-轨道耦合之间的协同作用，得益于界面工程的实现。
• 该器件在室温下稳定运行，标志着向实用化自旋电子器件迈出了关键一步。