本文選題：拓撲晶態(tài)絕緣體　切入點：表面態(tài)　出處：《南京大學》2017年碩士論文　論文類型：學位論文

【摘要】：隨著人們對量子霍爾效應的進一步深化,科學家們注意到了量子霍爾效應的具有特殊性質的邊界電流的無耗散的特性,極有可能打破摩爾定律的魔咒,即尺寸較小的半導體器件中電流的損耗和產熱問題。為了解決電流的損耗和發(fā)熱問題,科學家受到了微觀的奇特效應(帶負電的電子在繞原子核運動的過程中是沒有能量損耗的)的啟發(fā),可以利用量子霍爾效應的邊緣電流來實現(xiàn)。然而,量子霍爾效應的實現(xiàn)需要一個極強的外加磁場,這為現(xiàn)實應用量子霍爾效應帶了極大的困難。為了解決這一問題,科學界試圖找到不需要外加磁場就能夠實現(xiàn)量子霍爾效應的新方法。經過科學家的不懈努力,終于發(fā)現(xiàn)了量子反�；魻栃土孔幼孕魻栃@兩種可以不用外加磁場就能夠實現(xiàn)量子霍爾效應的奇特效應。量子自旋霍爾效應只需要在自旋軌道耦合作用足夠強大的條件下,便能夠產生邊緣電流。量子反�；魻栃饕ㄟ^利用材料自身產生的自發(fā)磁化來實現(xiàn)量子霍爾態(tài)。這兩種特殊量子效應的發(fā)現(xiàn)為實現(xiàn)量子霍爾效應的廣泛應用,帶了新的契機,科學家開始積極尋找能夠實現(xiàn)量子霍爾效應的新物態(tài),即二維的拓撲絕緣體。拓撲絕緣體的出現(xiàn)打開了量子霍爾效應的大門,為在人們日常使用的電子器件中實現(xiàn)量子霍爾效應帶來了希望,從而使制備低功耗的高速電子器件成為可能。近年來發(fā)現(xiàn)一種具有絕緣性的體能帶結構并且受時間反演對稱性保護的金屬表面態(tài)的新的物質形態(tài)—拓撲絕緣體。拓撲絕緣體的表面態(tài)不受非磁性雜質和晶體缺陷的影響,具有較高的穩(wěn)定性和遷移率,以及自旋和動量相互鎖定,在量子計算、自旋電子器件、新原理微納電子器件等方面具有廣闊的潛在應用前景。2012年,具有晶格對稱性的拓撲晶態(tài)絕緣體在理論上獲得證實,隨后碲化錫(SnTe)、碲化鉛(PbTe)被理論學家預測為新型拓撲晶態(tài)絕緣體,在它的高對稱性晶體表面如{001},{110}和{111}具有導電的拓撲態(tài),并在通過角分辨光電譜觀測到了存在的拓撲表面。由于低維納米結構具有較大的比表面積,從而能夠有效地減少體相輸運對表面的干擾作用因而表面態(tài)輸運可以更加容易被觀察到。現(xiàn)階段,輸運測量主要通過研究Aharonov-Bohm(AB)干涉效應和Shubnikov-de Haas(SdH)振蕩等方法驗證到高對稱性表面Dirac電子的存在。在這項工作中,我們首先通過化學氣相沉積法成功合成PbTe納米線,然后通過輸運測量,觀察到了其存在拓撲表面態(tài)的弱反局域化(WAL)效應和SdH量子震蕩(Shubnikov de Haas oscillations)。而且數(shù)據(jù)分析,我們得到低溫下,表面態(tài)的電導占到了總電導的～61%。我們的研究發(fā)現(xiàn)為PbTe納米線在自旋電子器件的應用向前推進了一步。
[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.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TQ134.33;TB383.1

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