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Quantum Transport in 2D Topological Insulator Device
No full text近年來，拓樸絕緣體已成為一個很有潛力的研究領域，它有可能是製作新一代自旋電子學元件和量子資訊的材料。在理論方面，量子力學的拓樸學應用有許多階段的研究。拓樸絕緣體的內部性質為一般的絕緣體，但是邊緣（表面）卻是導體，這是由於固體內部的電子能帶結構所決定的二維拓樸絕緣體具有特殊的邊緣（表面）態，這種特殊的量子態是由強自旋軌道耦合下所產生，而它的電導取決於邊緣態的數目。在二為拓樸絕緣體外加電場的情況下，兩個邊緣態上的電流會有相反的自旋，稱為量子自旋霍爾效應。一般認為，沿著邊緣狀態的電子不能被非磁性雜質散射，這是由於時間反演對稱性所導致。
在本論文中，我們考慮兩種對量子自旋霍爾效應影響的作用。首先是幾何形狀的影響，我們計算了兩種分支形狀的拓樸絕緣體的電流和自旋極化。我們的結果發現，分支狀的結構將增強自旋極化電流。第二是非磁性雜質的影響，我們研究非磁性雜質加入拓樸絕緣體的傳輸性質。雖然拓樸絕緣體的時間反演對稱性會保護邊緣態的電子不會被非磁性雜質散射，但邊緣的電子會穿隧到另一側的邊緣，導致電子的穿透係數下降。對於雜質的小樣本，傳輸係數甚至可以下降到零。最後，考慮分叉結構和雜質所構成的元件中，我們發現了電子同時擁有量子穿隧和量子干涉的效應，而這兩種效應會影響電子的傳輸方向。從這些結果推得此結構可以成為一種電子元件，藉由閘電位控制電流的開關，且具有自旋性質。以上這些性質皆是由Landauer formula進行數值研究。Recently, topological insulator is an emerged field in condensed matter physics and material science; it has been regarded as the materials which have potential applicate in the new generation of spintronics devices and quantum computer. For the theory, there are many phase and topology studies in the quantum mechanics in this topic. The topological insulator is the material that is insulating in the bulk but conducting on the edge (or surface). In two dimension, it exhibits the quantum spin Hall effect. The effect is caused by the strong spin-orbit coupling and the spin Hall conductance is determined by the number of edge state. It is believed that electron transport along the edge states cannot be backscattered by the non-magnetic impurity due to the time reversal symmetry.
In the thesis, we study the transport property of quantum spin Hall effect in defined geometries and effect caused by the impurities. First, we calculated the current and polarization on two types of branching topological insulators. Our results indicate that the branch structure will enhance the spin polarizing current. Second, the influences of impurity on the electron density and transmission of a finite topological insulator sample are studied. Although the time-reversal symmetry topology insulators will protect the edges of the electronic states cannot be scattering by non-magnetic impurity, however, electrons from one side can tunnel into the other side and the quantized conductance can be broken down. For a small sample with impurity, the transmission coefficient can even drop to zero for the crosswalk between the helical edge states at two sample sides. At last, a device is designed based in those two influences. We found that quantum tunneling and quantum interference occur in the same time, and both effects influence the direction of the electron. Those properties are studied numerically in the framework of Landauer Formalism.1 Introduction 1
1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Outline of Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Green Function in Quantum System 6
2.1 Tight-Binding Model building the Hamiltonian . . . . . . . . . . . . . . 6
2.2 Green Function and Local Density of State . . . . . . . . . . . . . . . . . 8
2.3 Landauer Step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1 Effective Hamiltonian and Self Energy . . . . . . . . . . . . . . 11
2.3.2 Surface Green function for Semi-Infinite System . . . . . . . . . 12
2.3.3 Landauer-Buttiker Formula . . . . . . . . . . . . . . . . . . . . 14
2.3.4 Landauer-Keldysh Formalism . . . . . . . . . . . . . . . . . . . 14
3 Topological Insulator 17
3.1 The Topology and Band Structure . . . . . . . . . . . . . . . . . . . . . 19
3.2 Topology and Topological Insulator . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Berry Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.2 Integer Quantum Hall Effect and TKNN Invariant (Chern Number) 21
3.2.3 Z2 Topological Insulator . . . . . . . . . . . . . . . . . . . . . . 22
3.3 2D Topological Insulator Material . . . . . . . . . . . . . . . . . . . . . 25
3.3.1 Zigzag Honeycomb Nano-Ribbon . . . . . . . . . . . . . . . . . 25
3.3.2 HgTe/CdTe Quantum Well . . . . . . . . . . . . . . . . . . . . . 27
4 Spin Transport Calculation for Branch-Shaped 2D Topological Insulator 30
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2 The Investigated Systems in ZNR . . . . . . . . . . . . . . . . . . . . . 31
4.2.1 Fork-Shaped ZNR . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.2 H-shaped ZNR . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3 The Investigated Systems in HgTe/CdTe Quantum Well . . . . . . . . . . 36
4.3.1 Fork-shaped HgTe/CdTe Quantum Well . . . . . . . . . . . . . . 36
4.3.2 H-shaped HgTe/CdTe Quantum Well . . . . . . . . . . . . . . . 38
4.4 Discussion and Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 41
5 Impurity Influence in Quantum Spin Hall Transport 44
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5.2 Impurity Potentail Matrix in Tight-Binding Model . . . . . . . . . . . . . 48
5.2.1 Clear Limit of Two Samples . . . . . . . . . . . . . . . . . . . . 49
5.3 In-gap Bound States Induced by Impurity . . . . . . . . . . . . . . . . . 50
5.4 Discussions and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . 51
6 The impurity in H-shaped Topological Insulator Device 57
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2 Clear Limit of Device . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6.3 Impurity Bound State and Interference Resonance . . . . . . . . . . . . . 59
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6.4 Discussions and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . 61
7 Summary and Outlook 64
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
7.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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