碲化铅纳米线的制备及其输运性质的研究

发布时间：2018-03-11 10:35

本文选题：拓扑晶态绝缘体　切入点：表面态　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：随着人们对量子霍尔效应的进一步深化,科学家们注意到了量子霍尔效应的具有特殊性质的边界电流的无耗散的特性,极有可能打破摩尔定律的魔咒,即尺寸较小的半导体器件中电流的损耗和产热问题。为了解决电流的损耗和发热问题,科学家受到了微观的奇特效应(带负电的电子在绕原子核运动的过程中是没有能量损耗的)的启发,可以利用量子霍尔效应的边缘电流来实现。然而,量子霍尔效应的实现需要一个极强的外加磁场,这为现实应用量子霍尔效应带了极大的困难。为了解决这一问题,科学界试图找到不需要外加磁场就能够实现量子霍尔效应的新方法。经过科学家的不懈努力,终于发现了量子反常霍尔效应和量子自旋霍尔效应这两种可以不用外加磁场就能够实现量子霍尔效应的奇特效应。量子自旋霍尔效应只需要在自旋轨道耦合作用足够强大的条件下,便能够产生边缘电流。量子反常霍尔效应主要通过利用材料自身产生的自发磁化来实现量子霍尔态。这两种特殊量子效应的发现为实现量子霍尔效应的广泛应用,带了新的契机,科学家开始积极寻找能够实现量子霍尔效应的新物态,即二维的拓扑绝缘体。拓扑绝缘体的出现打开了量子霍尔效应的大门,为在人们日常使用的电子器件中实现量子霍尔效应带来了希望,从而使制备低功耗的高速电子器件成为可能。近年来发现一种具有绝缘性的体能带结构并且受时间反演对称性保护的金属表面态的新的物质形态—拓扑绝缘体。拓扑绝缘体的表面态不受非磁性杂质和晶体缺陷的影响,具有较高的稳定性和迁移率,以及自旋和动量相互锁定,在量子计算、自旋电子器件、新原理微纳电子器件等方面具有广阔的潜在应用前景。2012年,具有晶格对称性的拓扑晶态绝缘体在理论上获得证实,随后碲化锡(SnTe)、碲化铅(PbTe)被理论学家预测为新型拓扑晶态绝缘体,在它的高对称性晶体表面如{001},{110}和{111}具有导电的拓扑态,并在通过角分辨光电谱观测到了存在的拓扑表面。由于低维纳米结构具有较大的比表面积,从而能够有效地减少体相输运对表面的干扰作用因而表面态输运可以更加容易被观察到。现阶段,输运测量主要通过研究Aharonov-Bohm(AB)干涉效应和Shubnikov-de Haas(SdH)振荡等方法验证到高对称性表面Dirac电子的存在。在这项工作中,我们首先通过化学气相沉积法成功合成PbTe纳米线,然后通过输运测量,观察到了其存在拓扑表面态的弱反局域化(WAL)效应和SdH量子震荡(Shubnikov de Haas oscillations)。而且数据分析,我们得到低温下,表面态的电导占到了总电导的～61%。我们的研究发现为PbTe纳米线在自旋电子器件的应用向前推进了一步。
[Abstract]:With the further deepening of the quantum Hall effect, scientists have noticed the non-dissipative properties of the quantum Hall effect's boundary current with special properties, which is likely to break the curse of Moore's Law. In order to solve the problem of current loss and heat generation, Scientists have been inspired by the peculiar microcosmic effects, in which negatively charged electrons move around the nucleus without loss of energy, and can be achieved using the edge current of the quantum Hall effect. The realization of quantum Hall effect requires a strong external magnetic field, which makes it very difficult to apply quantum Hall effect in reality. The scientific community is trying to find a new way to realize the quantum Hall effect without a magnetic field. Quantum anomalous Hall effect and quantum spin Hall effect, which can realize quantum Hall effect without external magnetic field, have finally been discovered. Quantum spin Hall effect only needs to be coupled in spin orbit. Under strong enough conditions, Quantum anomalous Hall effect is mainly realized by the spontaneous magnetization produced by the material itself. The discovery of these two special quantum effects is to realize the wide application of quantum Hall effect. With a new opportunity, scientists are actively looking for new physical states that can realize the quantum Hall effect, that is, two-dimensional topological insulators. The appearance of topological insulators opens the door to quantum Hall effect. For the realization of the quantum Hall effect in the electronic devices that people use in our daily life. Therefore, it is possible to fabricate low power consumption high speed electronic devices. In recent years, we have discovered a new material morphology, topological insulator, which has an insulating physical band structure and is protected by time inversion symmetry. The surface states of topological insulators are not affected by nonmagnetic impurities and crystal defects. With high stability and mobility, and the mutual locking of spin and momentum, it has broad potential applications in quantum computation, spin electronic devices, new principle micro and nano electronic devices, etc. In 2012, The topological crystal insulators with lattice symmetry have been theoretically confirmed, and then tin tetran telluride, lead lead telluride (PbTeTe) have been predicted by theorists to be new topological crystalline insulators, with conductive topologies on the surfaces of its highly symmetric crystals such as {001}, {110} and {111}. The topological surface was observed by angle resolved photovoltaic spectroscopy. Because of the large specific surface area of low-dimensional nanostructures, Therefore, the surface state transport can be observed more easily, so that the interference of bulk transport on the surface can be effectively reduced. The existence of highly symmetric surface Dirac electrons is verified by means of Aharonov-Bohmb interference effect and Shubnikov-de Haasn SdH oscillation. In this work, we successfully synthesized PbTe nanowires by chemical vapor deposition (CVD), and then by transport measurements. The weak anti-localization (WAL) effect of topological surface states and the SdH quantum oscillation Shubnikov de Haas oscillations have been observed. The surface-state conductance accounts for 61% of the total conductance. Our study shows that the application of PbTe nanowires in spin electronic devices is a step forward.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ134.33;TB383.1

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