Elucidating the mechanism of millimeter-long transport of photogenerated carriers in topological insulators

阐明拓扑绝缘体中光生载流子的毫米长传输机制

• 批准号: 2105161
• 负责人: Dong Yu
• 金额: $ 21万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-15 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2105161&HistoricalAwards=false
• 关键词: Elucidating; mechanism; millimeter; long; transport

NON-TECHNICAL SUMMARY:When light is absorbed by a material such as a semiconductor, the number of free electrons and holes increases, resulting in increased electrical conductivity. This phenomenon is known as photoconductivity. Understanding how photocarriers transport charge is key to many important applications such as solar cells and light detectors. A new category of fascinating materials, called topological insulators, has been discovered over the past decade. These materials have unique electronic properties at the surface and may find technological applications. The principal investigator’s research group has recently demonstrated unusual long-distance transport of photogenerated charge carriers in topological insulators at low temperatures. This suggests the formation of a quantum state known as an exciton condensate. If confirmed, this quantum state has potential uses in quantum computing. The aim of this project is to study this phenomena by a variety of experimental techniques and understand the physical mechanism behind it. This project also educates and trains undergraduate and graduate students in the rapidly advancing research area of quantum and spintronic devices and offers outreach activities targeting K-12 students.TECHNICAL SUMMARY:The PI’s recent experimental studies of three-dimensional topological insulators (TIs) have revealed unusual non-local photocurrent. Remarkably, the locally photogenerated carriers can transport over a millimeter along the intrinsic Sb-doped Bi2Se3 nanoribbons before recombination at up to 40 K, accompanied by an internal quantum efficiency as high as 60%. The observation of highly dissipationless transport of photogenerated carriers implies the formation of superfluidic exciton condensate. The goal of this project is to elucidate the physical mechanism of this highly nonlocal photocurrent generation. A suite of innovative spatially, temporally, and spectrally resolved techniques are applied to achieve this goal. Spatially resolved helicity-dependent photocurrent and the surface magneto-optical Kerr effect is investigated to understand the spin polarization and spin-momentum coupling of the photogenerated carriers at the TI surface. Infrared photocurrent spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and scanning tunneling spectroscopy (STS) will be performed to provide evidence for excitonic gap opening in the surface Dirac cone. Thinner and more intrinsic samples and topological materials beyond Bi2Se3 are studied to achieve higher critical temperatures. If confirmed, topological exciton condensation is expected to provide a new and exciting paradigm exploiting chiral superfluidic excitons towards high temperature quantum logic and novel spintronic devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术概要：当光被半导体等材料吸收时，自由电子和空穴的数量增加，导致导电性增加。这种现象被称为光导电性。了解光载流子如何传输电荷是许多重要应用的关键，如太阳能电池和光探测器。在过去的十年里，人们发现了一种叫做拓扑绝缘体的新材料。这些材料在表面具有独特的电子特性，可能会找到技术应用。首席研究员的研究小组最近展示了在低温下拓扑绝缘体中光产生的电荷载流子的不寻常的长距离传输。这表明形成了一种量子态，称为激子凝聚。如果得到证实，这种量子态在量子计算中有潜在的用途。该项目的目的是通过各种实验技术来研究这一现象，并了解其背后的物理机制。该项目还在量子和自旋电子器件快速发展的研究领域对本科生和研究生进行教育和培训，并为K-12学生提供外展活动。技术摘要：PI最近对三维拓扑绝缘体（TIs）的实验研究揭示了不寻常的非局部光电流。值得注意的是，局部光生成的载流子在40 K下重组之前可以沿着本态掺sb的Bi2Se3纳米带传输超过一毫米，并伴有高达60%的内部量子效率。观察到光生载流子的高度无耗散输运意味着超流激子凝聚的形成。本项目的目的是阐明这种高度非局域光电流产生的物理机制。为了实现这一目标，应用了一套创新的空间、时间和光谱分辨技术。研究了空间分辨的螺旋相关光电流和表面磁光克尔效应，以了解光生载流子在TI表面的自旋极化和自旋动量耦合。红外光电流光谱、角分辨光发射光谱（ARPES）和扫描隧道光谱（STS）将为表面狄拉克锥的激子间隙打开提供证据。研究了比Bi2Se3更薄、更本征的样品和拓扑材料，以达到更高的临界温度。如果得到证实，拓扑激子凝聚有望为利用手性超流体激子实现高温量子逻辑和新型自旋电子器件提供一个新的令人兴奋的范例。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Multiple andreev reflections in topological insulator nanoribbons

• DOI: 10.1016/j.cap.2021.12.003
• 发表时间: 2021-10
• 期刊: Current Applied Physics
• 影响因子: 2.4
• 作者: R. Kim;N. Kim;B. Kim;Yasen Hou;Dong Yu;Yong-Joo Doh

Modeling of the photocurrent induced by inverse spin Hall effect under local circularly polarized photoexcitation

• DOI: 10.1103/physrevb.104.205413
• 发表时间: 2021-11
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Kuen Wai Tang;B. Wang;H. C. Travaglini;D. Yu