近邻效应对石墨烯输运特性的调控

发布时间：2018-02-12 14:49

本文关键词： 低维物理石墨烯线性色散关系反常霍尔效应量子反常霍尔效应近邻效应等离激元弱局域化近场光学　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：固体的电子输运行为一定程度上依赖于固体的维度,对于二维材料,比如硅基的金属氧化物半导体场效应晶体管(MOSFET),作为现代科技的基石,就利用了局限在硅半导体表面的电荷层的特性。整数量子霍尔效应和分数量子霍尔效应是二维电子系统独特的现象,铜氧化物的高温超导性也被认为与材料的二维特性相关联。每当出现新奇的二维电子系统,总会在凝聚态物理掀起研究热潮。直到十几年前,二维范例还仅仅包含空间限制在量子阱沟道层,半导体异质结,或者表面反型层中的电子气。2004年情况发生了改变,人们发现可以从石墨块材中提取出独立的原子层。这种二维晶体尽管只有一个原子的厚度,却可以稳定的存在。这种材料叫做石墨烯,是本论文的主要研究对象。石墨烯是一个在材料科学和凝聚态物理领域快速发展的新星,这种严格的二维材料展现了特别高的晶体质量和电学特性,尽管发展历史并不长,石墨烯已经汇聚了大量的新物理和潜在的应用。一方面,由于石墨烯本身非平凡的电子能谱,石墨烯引领了相对论凝聚态物理的新范例,一些在高能物理很难看到的量子相对论现象,现在可以在石墨烯体系中获得更便捷的研究。另一方面,石墨烯代表了新类型的单原子层材料,为低维物理基础研究和应用提供了新的体系平台和路径。本论文结构安排如下:第一章,首先简要介绍石墨烯的单原子层晶体结构,特有的线性色散关系和能带结构。随后概述石墨烯在输运方面的特性,包括它的双极性调控,量子干涉效应,独特的半整数量子霍尔效应,并对反常霍尔效应和量子反常霍尔效应作简要介绍。第二章,简述样品制备和低温测量方法,包括石墨烯的剥离,转移,表征过程,以及微纳加工技术辅助制作石墨烯器件,然后对材料生长常用的激光分子束外延技术作说明,最后对低温输运测试使用的系统设备作简介。第三章,我们通过功能衬底近邻方式,引入和增强石墨烯的磁性,最终目的是实现石墨烯的量子反常霍尔效应。基于本实验室有一定的锰氧化物生长经验,首先选用磁性绝缘衬底Pr0.8Ca0.2MnO3,其上放置石墨烯,制作基本的霍尔器件。测量后我们发现,以Pr0.8Ca0.2MnO3为介电层,栅压很难调控载流子浓度。后来我们选用另一种磁性绝缘衬底LaMnO3,发现可以有效调节石墨烯的载流子浓度。同时,LaMnO3上石墨烯的霍尔电阻表现出非线性。这种霍尔电阻的非线性无法通过双载流子模型拟合,尤其对于费米能级远离Dirac点的情况。进一步,我们发现可以通过添加反常霍尔项很好地拟合实验数据,反常霍尔的发现标志着对石墨烯引入了长程铁磁序。另外,磁阻最小值偏离零场,我们认为可能是自旋轨道耦合增强的体现。第四章,研究石墨烯与等离激元复合体系的输运。固体中不同准粒子的相互作用导致了很多有趣的量子效应的出现,而对于集体等离激元激发如何影响电子的量子输运到目前还没有深刻认知。实验上我们使用金纳米颗粒向近邻石墨烯引入等离激元,首次证实当电子-等离激元耦合引入时,石墨烯电子的量子相干特性有实质上的增强,对应的量子相干长度几乎是原来的三倍。进一步我们提出了一个微观模型解释这一奇特的发现,强调石墨烯等离激元在抑制电子-电子退相位中的关键作用。这一新奇的创新性的概念,即等离激元增强量子相干,为研究准粒子间相互作用开辟了新的视野,有利于探索非平凡的量子现象。第五章,研究了石墨烯近邻自旋轨道耦合的输运特性和近场光学。我们选择具有很强自旋轨道耦合的材料KTaO3作为衬底,期望可以通过近邻效应增强石墨烯的自旋轨道相互作用。首先使用输运手段探测器件的非局域自旋霍尔效应,发现明显高于欧姆贡献的非局域信号,还没有看到面内场自旋进动现象,无法确定是否来源于石墨烯自旋轨道耦合增强,有待进一步研究。另一方面,最近石墨烯的进场光学研究逐渐兴起,通过改变其衬底环境有望可以调控等离激元的激发和传播。基于此我们使用近场光学显微镜(SNOM)探测graphene/KTaO3体系的表面等离激元,得到的驻波图样明显不同于一般氧化硅衬底上的石墨烯,发现激发的等离激元具有多模式特性,证实了边缘激发模式的存在。
[Abstract]:Solid electronic transport behavior to a certain extent depends on the solid dimensions for the two-dimensional material, such as silicon metal oxide semiconductor field effect transistor (MOSFET), as the cornerstone of modern science and technology, characteristics on the use of limitations in the surface charge layer of silicon. The integer quantum Holzer effect and fractional quantum Holzer effect is a phenomenon unique two-dimensional electronic systems, high temperature superconductivity in copper oxides is also thought to be associated with the characteristics of two-dimensional materials. When a two-dimensional electron system of novel, always raised the research upsurge in condensed matter physics. Until a decade ago, two examples also contain only limited space in the quantum well channel layer, semiconductor heterojunction. Or the surface inversion layer electron gas.2004 changed, people found that can be extracted from the graphite block in atomic layer independent. This two-dimensional crystal as only One atom thickness can exist stably. This material is called graphene, is the main research object of this thesis. Graphene is a rapid development in material science and condensed matter physics field star, two-dimensional materials this strict show the crystal quality and electrical properties is particularly high, although the history is not long, graphene has brought together a large number of new physics and potential applications. On the one hand, because of the graphene nontrivial electron spectrum of graphene leads the new paradigm of relativistic condensed state physics, some in high energy physics difficult to see quantum relativistic phenomenon, can now get more convenient in the study graphene system. On the other hand, graphene represents a single atomic layer material of new type, provide a system platform and a new path for the research and application of low dimensional physical basis. This paper is organized as follows: first Chapter one briefly introduces the crystal structure of atomic layer graphene, linear dispersion relation and unique band structure. Then an overview of graphene on transport properties, including bipolar regulation, quantum interference effect, half integer quantum Holzer effect is unique, and gives a brief introduction to the anti Holzer effect and often quantum anomalous Holzer effect. In the second chapter, the sample preparation and temperature measuring method, stripping, including graphene transfer, process characterization, and micro nano processing technology made graphene devices and materials, laser molecular beam epitaxy growth commonly stated, at the end of the low temperature transportation system used for testing equipment introduction. In the third chapter, we introduce the way through the function of substrate and enhanced magnetic affinity, graphene, the ultimate aim is the quantum anomalous Holzer effect of graphene. Based on the laboratory have certain manganese oxide Growth experience, the first choice of magnetic Pr0.8Ca0.2MnO3 are arranged on the insulating substrate, graphene, making Holzer devices. After the measurement we found that using Pr0.8Ca0.2MnO3 as the dielectric layer, the gate voltage is difficult to control the carrier concentration. Then we use another magnetic insulating substrate LaMnO3, showed that the carrier concentration can effectively regulate the graphene. At the same time, Holzer resistance LaMnO3 graphene exhibits nonlinear. The nonlinear Holzer resistance cannot pass through the double carrier model, especially for the Fermi level from Dirac points. Further, I have found that by adding a anomalous Holzer well fit the experimental data, the anomalous Holzer found marks on the graphene is introduced the long-range ferromagnetic order. In addition, the minimum reluctance values deviate from the zero field, we think it might be the manifestation of enhanced spin orbit coupling. In the fourth chapter, research on graphene and plasma Polariton transport composite system. The interaction of different solid quasi particles led to the emergence of many interesting quantum effects, and for the collective plasmon excitation affects the electronic quantum transport is still not profound cognition. Experiment we use gold nanoparticles were introduced to near neighbor graphene plasmon yuan, for the first time that when the electron plasmon coupling is introduced, the quantum coherence properties of graphene electronics have increased substantially, the corresponding quantum coherence length is almost three times the original. Further we propose a microscopic model to explain this strange discovery, emphasizing the graphene plasmon in inhibition of electron electron back key role in phase. The concept of this novel innovation, namely plasmon enhanced quantum coherence, for the study of quasi particle interactions has opened up new horizons, to explore the nontrivial quantum current Like. The fifth chapter studied the transport properties of graphene nearest neighbor spin orbit coupling and near-field optics. We have strong spin orbit coupling material KTaO3 as substrate, the expectation can enhance the spin orbit interaction of graphene by neighbor effect. First use of transport in the detector of the nonlocal spin Holzer effect non local signal, found was significantly higher than that of ohmic contribution, have not seen the spin precession phenomenon, can not determine whether from graphene spin orbit coupling, needs further study. On the other hand, recent research approach optical graphene gradually rise, by changing the substrate environment is expected to be regulated from the excitation and propagation polaritons. Based on this we use the near-field optical microscope (SNOM) detection system of graphene/KTaO3 surface plasmon, the standing wave pattern is significantly different from the general The graphene on the silicon oxide substrate has been found to have multiple modes of excitation, which confirms the existence of the edge excitation mode.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.71

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