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类型 基础研究 预答辩日期 2017-11-20
开始(开题)日期 2016-08-23 论文结束日期 2017-08-23
地点 南高院四楼会议室 论文选题来源 国家自然科学基金项目     论文字数 5 (万字)
题目 石墨烯条带中的自旋相关性质及其调控
主题词 石墨烯,Rashba自旋-轨道耦合,自旋磁化率,自旋输运,自旋量子关联
摘要 传统电子器件的微型化已经越来越接近量子极限,摩尔定律面临重大挑战,因此工业界开始关注新兴技术的发展动向。自旋电子学将电子自旋相关效应与传统的微电子学相结合,为下一代全新功能的微电子器件的研发指明了方向。探索理想的自旋电子学材料,研究其自旋相关物理性质,进而开发全新功能的自旋器件,成为了当前研究的热点。 锯齿型石墨烯纳米带(ZGNR)由于具有独特的边缘效应,即自旋极化边缘态,利用这一磁学性质可以设计一些新奇的自旋电子学器件,因此备受人们的关注。我们通过第一性原理计算研究了褶皱对含双空位缺陷的ZGNR的自旋极化边缘态及其电学性质的影响。结果发现,随着纳米带褶皱幅度的增大,系统经历了反铁磁→铁磁→无磁性的磁性相变。相应地,系统的电学性质经历了半导体→金属→半导体的转变。如果将纳米带沉积在处于拉伸状态的某种特殊弹性衬底上,通过缓慢释放和再度拉伸可以对褶皱进行控制,进而实现对纳米带自旋极化边缘态和电学性质的调控。 虽然ZGNR作为自旋电子学材料有潜在优势,但是直接利用ZGNR的自旋极化边缘态还存在困难。一方面很难制备完美的ZGNR;另一方面这种边缘磁性容易受温度、缺陷或杂质等因素的影响而遭到破坏。因此,如何才能有效实现石墨烯中电子的自旋极化,并且能够对其自旋状态进行良好的控制,是一个非常值得研究的问题。考虑到扶手椅型石墨烯纳米带(AGNR)具有丰富的电学性质,且完美的AGNR已经可以在实验上制备,如果能够使其产生自旋极化,就有可能在自旋电子学方面得到应用。为此,我们利用线性响应理论研究了Rashba自旋-轨道耦合(RSOC)作用下的AGNR在外振荡磁场中的自旋磁化率。结果表明:通过改变纳米带宽度,或外场频率,或RSOC强度,使得满足共振条件而引起电子在Rashba自旋劈裂子能带间发生跃迁,改变系统沿磁场方向的自旋取向分布,这样就可以实现AGNR中的电子自旋在室温下的有效磁化。而且,在这个过程中自旋磁化率的大小也可以通过不同的共振频率或RSOC进行控制。该方案完全不存在电导不匹配问题,因此可以有效解决自旋注入效率低下的问题。 自旋极化载流子成功注入到石墨烯以后,要实现应用我们还必须研究自旋输运与调控问题。为此,我们利用狄拉克理论研究了RSOC作用下准带状单层石墨烯中的克莱恩隧穿现象,得到了透射系数的解析解。在透射系数的基础上,我们进一步推导了自旋相关电导,研究了透射电子的自旋极化。通过改变门压势垒或RSOC强度,我们可以对自旋输运和透射电子的自旋状态进行有效的调控。在此理论基础上我们提出了一种门压可控的多功能自旋器件,既可以用作晶体管,也可以用于自旋过滤,自旋转换或电子束准直等。 此外,由于石墨烯中的自旋相干时间较长,因此其自旋还可以作为理想的固态量子比特。基于有效自旋理论,我们研究了处于温度为T的热库下的手性石墨烯纳米带中的量子纠缠与量子失谐,讨论了温度,纳米带宽度,自旋粒子间的相对位置,以及电子间排斥势对量子关联的影响。结果发现在室温下,较窄的纳米带中最近邻反铁耦合的自旋粒子间的量子纠缠几乎接近于最大纠缠。进一步我们利用该热纠缠态来实现纠缠态的隐形传输。从理论上阐明了成功实现纠缠态的传输,量子通道的纠缠度和输入态的纠缠度之间必须要满足的关系,从而揭示了在基于石墨烯这样的固态系统中进行量子信息处理的可能性。
英文题目 SPIN-DEPENDENT PROPERTIES AND CONTROL IN GRAPHENE RIBBONS
英文主题词 graphene, Rashba spin-orbit coupling, spin susceptibility, spin transport, spin quantum correlation
英文摘要 Moore’s law is confronted with great challenges because electronic miniaturization is increasingly close to the quantum limit, and thus the industrial community turns their attentions to new technologies. Spintronics combines electron spin-dependent effects with microelectronics, which illuminates the way to develop the next generation of new functional microelectronic devices. As a result, exploring perfect spintronic functional materials, studying their spin-dependent physical properties, and then developing new spin devices become a very hot topic recently. Zigzag graphene nanoribbons (ZGNRs) have attracted extensive interest due to the unique edge effect, i.e. the spin-polarized edge states which are shown to be very promising for applications in novel spintronics devices. Here the influences of corrugations on the spin-polarized edge states and electronic properties of ZGNR with divacancy defects are investigated by means of the first principle calculations. The results show that when the magnitude of corrugation increases the system experiences an antiferromagnetism- ferrimagnetism-nonmagnetism phase transition, while for the electronic properties the system exhibits a semiconductor-metal-semiconductor transition. If the nanoribbon is attached to a pre-stretched elastomer substrate, its corrugations can be controlled by slowly releasing and straining the substrate, thus realizing the manipulation of spin-polarized edge states and electronic properties in the nanoribbon. ZGNRs are regarded as preponderant spintronics materials. However, there exist difficulties for using the edge magnetism directly. On the one hand, it is very difficult to make perfect ZGNRs, and on the other hand the edge states are easily destroyed by temperature, edge defects or impurities. Thus, how to effectively realize the spin polarization and spin control in graphene is worth studying. Motivated by the recent synthesis of perfect AGNRs in laboratory and their multiple electronic properties, it seems very possible for AGNRs to be applied in spintronics, if the electron spins in AGNRs can be made polarized. Using the linear response theory, the spin susceptibilities are studied in AGNRs with Rashba spin-orbit coupling (RSOC) under an oscillating magnetic field. It is shown that by tuning the field frequency, RSOC, or ribbon width to satisfy the resonance condition that can cause the electron transitions between RSOC-induced spin-split subbands, the spins in AGNRs will be effectively magnetized at room temperature due to the changes of spin-oriented distribution along the field direction. Moreover, in this process the magnitude of spin magnetization can also be flexibly manipulated by selecting different resonant frequency, or RSOC. This scheme does not exist the conductance mismatch problem, and thus can solve the low efficiency issue of spin injection. After spin polarized carriers are injected into graphene, the issues of spin transport and control must be studied in order to realize spintronics applications. Based on the Dirac theory, Klein tunneling is investigated in the quasi ribbonlike single layer graphene with Rashba spin-orbit coupling, and the transmission coefficients are obtained analytically. Using the transmission coefficients, the spin-resolved conductance is derived, and spin polarization of transmitted electrons are studied. By tuning potential barrier or RSOC strength, the spin transport and spin states of transmitted electrons can be effectively manipulated. According to the theoretical analyses, a conceptive gate-tunable spin device is presented, which can qualify as a transistor and also can realize the functions such as spin filtration, spin switch, or electron beam collimation. In addition, electron spins in graphene have long coherence times, and thus the spins are very promising candidates for the solid-state qubits. Based on the effective spin theory, the quantum entanglement and quantum discord are investigated in chiral graphene nanoribbons (CGNRs) thermalized with a reservoir at temperature T, and the influences of temperature, ribbon width, relative location between two spins, and Coulomb repulsion among electrons on quantum correlations are discussed. The results show that quantum entanglement between nearest-neighbor spins coupled antiferromagnetically in narrow CGNRs is approximately close to the maximum at room temperature. Further, this type of thermal entanglement is employed to realize the entanglement teleportation. For the successful entanglement teleportation, the relationship between channel and input entanglement is clarified theoretically, thus opening the possibility for quantum information processing in graphene-based solid system.
学术讨论
主办单位时间地点报告人报告主题
IEEE纳米技术委员会南京分会;东南大学电子科学与工程学院;东南大学—FEI 纳皮米中心 2016年12月23日 MEMS教育部重点实验室 南高院4楼会议室 Pro. Yimei Zhu Tracking Ionic Transport and Electrochemical Reactions in Individual Nanoparticles for Energy
IEEE纳米技术委员会南京分会;东南大学电子科学与工程学院;东南大学—FEI 纳皮米中心 2016年12月6日 MEMS教育部重点实验室 南高院4楼会议室 Dr. Zhong Li In-situ atomic-scale TEM studies on plastic deformation of nanoscale
IEEE纳米技术委员会南京分会;东南大学电子科学与工程学院;东南大学—FEI 纳皮米中心 2016年7月8日 MEMS教育部重点实验室 南高院4楼会议室 Pro. Hoe Tan Semiconductor nanowires for optoelectronic and energy application
IEEE纳米技术委员会南京分会;东南大学电子科学与工程学院;东南大学—FEI 纳皮米中心 2016年6月21日 MEMS教育部重点实验室 南高院4楼会议室 Pro. Xiangfeng Duan 2D Electronics: Opportunities and Challenges
IEEE纳米技术委员会南京分会;东南大学电子科学与工程学院;东南大学—FEI 纳皮米中心 2016年5月18日 MEMS教育部重点实验室 南高院4楼会议室 Pro. Pedro Gomez-Romero Graphene and Graphene-based Hybrids for Energy Storage
东南大学—FEI 纳皮米中心 2016年11月10日 MEMS教育部重点实验室 南高院4楼会议室 谭小东 手性石墨烯纳米带中的自旋量子关联
东南大学—FEI 纳皮米中心 2016年6月16日 MEMS教育部重点实验室 南高院4楼会议室 谭小东 石墨烯中的电子自旋特性及其调控
东南大学—FEI 纳皮米中心 2015年11月12日 MEMS教育部重点实验室 南高院4楼会议室 谭小东 石墨烯自旋电子学
东南大学—FEI 纳皮米中心 2015年6月11日 MEMS教育部重点实验室 南高院4楼会议室 谭小东 石墨烯电磁学特性的调控及自旋电子学
     
学术会议
会议名称时间地点本人报告本人报告题目
2017 2nd International Conference on Materials Engineering and Nanotechnology 2017年5月12日—5月14日 马来西亚 吉隆坡 Quantum correlations and entanglement teleportation in chiral graphene nanoribbons
2017 2nd International Conference on Material Engineering and Smart Materials 2017年6月23日—6月25 北京 Electronic and Magnetic Properties of Corrugated Zigzag Graphene Nanoribbons With Divacancy Defects
     
代表作
论文名称
The electronic and magnetic properties of corrugated zigzag graphene nanoribbons with divacancy defe
Entanglement teleportation via thermal Wannier edge states in a chiral graphene nanoribbon
Gate tunable spin transport in graphene with Rashba spin-orbit coupling
Spin susceptibilities in armchair graphene nanoribbons with Rashba spin-orbit coupling
Quantum correlations in chiral graphene nanoribbons
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
万贤纲 正高 教授 博导 南京大学
魏昂 正高 教授 博导 南京邮电大学
徐春祥 正高 教授 博导 东南大学
倪振华 正高 教授 博导 东南大学
薛鹏 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
徐涛 其他 讲师 东南大学