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Superlattices And Quantum Spin Hall States In Graphene And Hexagonal Boron Nitride Heterostructures
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Book Synopsis Superlattices and Quantum Spin Hall States in Graphene and Hexagonal Boron Nitride Heterostructures by : Javier Daniel Sanchez-Yamagishi
Download or read book Superlattices and Quantum Spin Hall States in Graphene and Hexagonal Boron Nitride Heterostructures written by Javier Daniel Sanchez-Yamagishi and published by . This book was released on 2015 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two-dimensional (2d) layered materials, such as graphene and hexagonal boron nitride (hBN), can be isolated separately and then stacked together to form heterostructures with crystalline interfaces between the layers. In this thesis, I present a series of experiments which explore the quantum transport of electrons in heterostructures made from graphene and hBN. Depending on the relative alignment, or "twist", between the layers, a crystal of hBN can be either a non-perturbing substrate for the graphene, or a method to induce a band gap and superlattice potential for the graphene electrons. In the case of two stacked graphene layers, a relative twist can electronically decouple the layers from each other, despite a tiny 0.34nm interlayer spacing. This twist-dependent physics can be used to realize new electronic states in graphene, especially in the presence of strong magnetic fields and electron-electron interactions. By applying a strong tilted magnetic field to graphene which is decoupled from its hBN substrate, we are able to realize a quantum spin Hall state and measure its electronic properties. An analogous bilayer quantum spin Hall state is also realized in twisted bilayer graphene, by taking advantage of the twist decoupling between the layers and the effects of electron-electron interactions. A different set of experiments explores the competition of a magnetic field with the effects of the superlattice potential which arises when a graphene sheet is nearly aligned to its hBN substrates. The large superlattice potential allows us to study graphene transport in Hofstadter's butterfly-the fractal spectrum for electrons under the simultaneous influence of a lattice and a magnetic field.
Book Synopsis Correlations in Moiré Heterostructures by : Aaron Layne Sharpe
Download or read book Correlations in Moiré Heterostructures written by Aaron Layne Sharpe and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Moiré patterns in van der Waals heterostructures are a readily realizable class of 2D superlattices with electronic properties distinct from those of the parent materials that can be controlled by the composition and relative orientations of layers. The large artificial superlattice generates minibands that disperse on a finer energy scale in a significantly smaller mini Brillouin zone. I begin with transport measurements in highly aligned graphene/hexagonal boron nitride (hBN) heterostructures, a high electron mobility superlattice with miniband edges and Van Hove singularities that are accessible via electrostatic gating. By using recently developed absorptive pinhole collimators, consisting of absorptive sidewalls between a pair of collinear slits, it is possible to populate and detect a narrow window of $k$-states. Low-field transport measurements yield results consistent with ballistic Monte Carlo simulations based on numerical bandstructure calculations when the superlattice has been tuned to exhibit non-circular Fermi surfaces. Subsequent scanning gate measurements spatially image the non-circular Fermi surface, raising the possibility of using absorptive pinhole collimators as geometric valley filters. A number of moiré superlattices have recently emerged that exhibit flat electronic bands, making them ideal for exploring strongly correlated physics. The flat bands in magic-angle twisted bilayer graphene (tBLG) and ABC-trilayer graphene aligned with hBN (ABC-TLG/hBN) have been shown to give rise to correlated insulators [1,2]. An amazing recent discovery is that tBLG becomes superconducting when doped slightly away from two holes per site, reminiscent of high temperature superconductors [3]. Understanding the mechanism of high-transition-temperature (high-$T_c$) superconductivity is a central problem in condensed matter physics. It is highly desirable to study a tunable Hubbard system, in which systematic investigations of the unconventional superconductivity and its evolution with the Hubbard parameters can deepen our understanding of high-$T_c$ superconductivity. I begin with a report of signatures of tunable superconductivity in ABC-TLG/hBN. Unlike in tBLG, theoretical calculations show that under a vertical displacement field, the ABC-TLG/hBN heterostructure features an isolated flat valence miniband associated with a Hubbard model on a triangular superlattice [2,4]. Signatures of superconductivity emerge below 1 kelvin for the electron- and hole-doped sides of the one-quarter-filling correlated state. The electronic behaviour in the ABC-TLG/hBN superlattice is expected to depend sensitively on the interplay between electron--electron interactions and the miniband bandwidth. By varying the vertical displacement field, transitions from the candidate superconductor to correlated insulator and metallic phases are observed. Superconductivity is one of many possible ground states in flat band systems when electron-electron interactions dominate. I present evidence of an incipient Chern insulating state at integer filling of the flat band in both tBLG and ABC-TLG/hBN. Notably, in tBLG, the magnetization of the sample can be reversed by applying a small direct current. Additionally, when tilting a tBLG sample in an external magnetic field, the ferromagnetism is highly anisotropic. Because spin-orbit coupling is negligible in graphene [5], such behavior is unlikely to come from spin, but rather favors theories in which the ferromagnetism is orbital. For an in-plane field larger than $5\ \mathrm{T}$, the out-of-plane magnetization is destroyed, suggesting a transition to a new phase. At integer filling of these strongly correlated moiré systems, it is natural to expect the possibility of spontaneous spin/valley polarization. However, there is the possibility of fractional quantum anomalous Hall insulators at fractional filling if interactions are strong enough. I report evidence of ferromagnetism at fractional filling in both tBLG and ABC-TLG/hBN. These states depend very sensitively on the control parameters in the moiré system, to the point where the results in tBLG were not repeatable between cooldowns of the same device. However, the state in ABC-TLG/hBN is much more robust, exhibiting prominent ferromagnetic hysteresis behavior with large anomalous Hall resistivity in a broad region of density. In ABC-TLG/hBN, not only the magnitude of the anomalous Hall signal, but also the sign of the hysteretic ferromagnetic response can be modulated by tuning the carrier density and displacement field. The plethora of interesting ground states found thus far highlights the exciting opportunities for exploring strongly correlated physics enabled in moiré superlattices.
Book Synopsis Bridging Hubbard Model Physics and Quantum Hall Physics in Graphene Moire Superlattices by : Yahui Zhang (Ph.D.)
Download or read book Bridging Hubbard Model Physics and Quantum Hall Physics in Graphene Moire Superlattices written by Yahui Zhang (Ph.D.) and published by . This book was released on 2019 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is focused on the strongly correlated physics of graphene moiré superlattices formed in twisted bilayer graphene (TBG), twisted double bilayer graphene (TDBG) and ABC trilayer graphene aligned with hexagon boron nitride (TLG-hBN). First, I will show that the physics of these systems can be divided into two categories: (1)The nearly-flat bands have non-zero valley Chern number, which leads to "quantum Hall physics" including integer and fractional quantum anomalous Hall effect and composite fermi liquid (CFL) physics. (2) The narrow bands have trivial band topology. In this case the essential physics is captured by a Hubbard like lattice model similar to that of the high T[subscript c] cuprates. Both of the above two classes have already been realized in the experiments. I will discuss how current and future experiments on these moiré materials can deepen our understanding of the cuprate physics and quantum Hall physics. In addition, I will also propose several new phases in moiré systems, which have never been studied before. These include featureless and orthogonal pseudogap metals and quantum Hall spin liquids.
Book Synopsis Novel Phenomena Driven by Interactions and Symmetry Breaking in Graphene by : François Amet
Download or read book Novel Phenomena Driven by Interactions and Symmetry Breaking in Graphene written by François Amet and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The electronic properties of graphene are well described by a non-interacting Dirac Hamiltonian with an internal symmetry associated with spin and valley, an additional degree of freedom due to the hexagonal crystal lattice of graphene. As a result, graphene exhibits a variety of peculiar phenomena such as an anomalous quantum Hall effect or the absence of backscattering. However, this model breaks down in extremely clean samples, as interactions between electrons and with the substrate become relevant. In this work, we discuss some of the properties of graphene and boron nitride heterostructures, in particular the patterns of broken symmetry phases one can observe in these devices. First, we observe modification in the electronic band structure of graphene due to its interactions with the substrate. The sub lattice symmetry of the Dirac Hamiltonian is broken, which opens an energy gap at charge neutrality, in addition to superlattice Dirac points due to the moire pattern that graphene forms on boron nitride. We then describe transport at high magnetic field, in the quantum Hall regime, where Coulomb interactions yield spin and valley quantum Hall ferromagnetic phases, with polarized one dimensional states propagating along the edges of the device. Using dual-gated device geometries, we can address the transport properties of these edge states and in particular how they equilibrate, depending on their polarization (or absence thereof). At even higher fields, new collective ground states emerge in the fractional quantum Hall regime. In extremely clean samples we observe a plethora of fractional quantum Hall states, described by the composite fermion theory, with unexpected patterns of stability and spin polarizations. Observing these electronic phenomena requires an outstanding device quality with carrier mobility exceeding one million cm2/Vs. We describe in this work the fabrication and characterization methods that allow us to control the quality of graphene/boron nitride, as well as novel device geometries allowing for high quality bipolar transport in graphene.
Book Synopsis Electronic Properties of Graphene Heterostructures with Hexagonal Crystals by : John R. Wallbank
Download or read book Electronic Properties of Graphene Heterostructures with Hexagonal Crystals written by John R. Wallbank and published by Springer. This book was released on 2014-06-13 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last decade has witnessed the discovery of, and dramatic progress in understanding the physics of graphene and related two-dimensional materials. The development of methods for manufacturing and aligning high-quality two-dimensional crystals has facilitated the creation of a new generation of materials: the heterostructures of graphene with hexagonal crystals, in which the graphene electrons acquire new, qualitatively different properties. This thesis provides a comprehensive theoretical framework in which to understand these heterostructures, based on the tight binding model, perturbation theory, group theory and the concept of the moire superlattice (all of which are elucidated). It explains how graphene heterostructures provide new opportunities for tailoring band structure, such as creating additional Dirac points or opening band gaps and how they manifest themselves in transport measurements, optical absorption spectra and the fractal Hofstadter spectra. Also considered are the heterostructures of bilayer graphene and resonant tunneling in aligned graphene/insulator/graphene devices.
Book Synopsis Introduction to Graphene-Based Nanomaterials by : Luis E. F. Foa Torres
Download or read book Introduction to Graphene-Based Nanomaterials written by Luis E. F. Foa Torres and published by Cambridge University Press. This book was released on 2020-01-30 with total page 479 pages. Available in PDF, EPUB and Kindle. Book excerpt: Graphene is one of the most intensively studied materials, and has unusual electrical, mechanical and thermal properties, which provide almost unlimited potential applications. This book provides an introduction to the electrical and transport properties of graphene and other two-dimensional nanomaterials, covering ab-initio to multiscale methods. Updated from the first edition, the authors have added chapters on other two-dimensional materials, spin-related phenomena, and an improved overview of Berry phase effects. Other topics include powerful order N electronic structure, transport calculations, and ac transport and multiscale transport methodologies. Chapters are complemented with concrete examples and case studies, questions and exercises, detailed appendices and computational codes. It is a valuable resource for graduate students and researchers working in physics, materials science or engineering who are interested in the field of graphene-based nanomaterials.
Book Synopsis Spin Transport in Graphene - Hexagonal Boron Nitride Van Der Waals Heterostructures by :
Download or read book Spin Transport in Graphene - Hexagonal Boron Nitride Van Der Waals Heterostructures written by and published by . This book was released on 2018 with total page 175 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Handbook of Graphene, Volume 3 by : Mei Zhang
Download or read book Handbook of Graphene, Volume 3 written by Mei Zhang and published by John Wiley & Sons. This book was released on 2019-06-11 with total page 618 pages. Available in PDF, EPUB and Kindle. Book excerpt: The third volume in a series of handbooks on graphene research and applications Graphene is a valuable nanomaterial used in technology. This handbook is focused on Graphene-Like 2D Materials. The Handbook of Graphene, Volume 3 covers topics that include planar graphene superlattices; magnetic and optical properties of graphene materials with porous defects; and nanoelectronic application of graphyne and its structural derivatives.
Book Synopsis Nanomechanics in van der Waals Heterostructures by : Matthew Holwill
Download or read book Nanomechanics in van der Waals Heterostructures written by Matthew Holwill and published by Springer. This book was released on 2019-05-04 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: Micro/nano-mechanical systems are a crucial part of the modern world providing a plethora of sensing and actuation functionalities used in everything from the largest cargo ships to the smallest hand-held electronics; from the most advanced scientific and medical equipment to the simplest household items. Over the past few decades, the processes used to produce these devices have improved, supporting dramatic reductions in size, but there are fundamental limits to this trend that require a new production paradigm. The 2004 discovery of graphene ushered in a new era of condensed matter physics research, that of two-dimensional materials. Being only a few atomic layers thick, this new class of materials exhibit unprecedented mechanical strength and flexibility and can couple to electric, magnetic and optical signals. Additionally, they can be combined to form van der Waals heterostructures in an almost limitless number of ways. They are thus ideal candidates to reduce the size and extend the capabilities of traditional micro/nano-mechanical systems and are poised to redefine the technological sphere. This thesis attempts to develop the framework and protocols required to produce and characterise micro/nano-mechanical devices made from two-dimensional materials. Graphene and its insulating analogue, hexagonal boron nitride, are the most widely studied materials and their heterostructures are used as the test-bed for potential device architectures and capabilities. Interlayer friction, electro-mechanical actuation and surface reconstruction are some of the key phenomena investigated in this work.
Book Synopsis Twist Angle Physics in Graphene Based Van Der Waals Heterostructures by : Yuanhong Luo (Ph. D.)
Download or read book Twist Angle Physics in Graphene Based Van Der Waals Heterostructures written by Yuanhong Luo (Ph. D.) and published by . This book was released on 2018 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, I present my experimental work on twisted bilayer graphene, a van der Waals heterostructure consisting of two graphene sheets stack on top of each other. In particular, the twist angle is a new degree of freedom in this system, and has an important effect in the determination of its transport properties. The work presented will explore the twist-dependent physics in two regimes: the large twist angle and small twist angle regimes. In the large-twist angle limit, the two sheets have little interlayer interactions and are strongly decoupled, allowing us to put independent quantum Hall edge modes in both layers. We study the edge state interactions in this system, culminating in the formation of a quantum spin Hall state in twisted bilayer graphene. In the small twist angle limit, interlayer interactions are strong and the layers are strongly hybridized. Additionally, a new long-range moiré phenomenon emerges, and we study the effects of the interplay between moiré physics and interlayer interactions on its transport properties.
Book Synopsis The Physics of Graphene by : Mikhail I. Katsnelson
Download or read book The Physics of Graphene written by Mikhail I. Katsnelson and published by Cambridge University Press. This book was released on 2020-03-19 with total page 441 pages. Available in PDF, EPUB and Kindle. Book excerpt: Leading graphene research theorist Mikhail I. Katsnelson systematically presents the basic concepts of graphene physics in this fully revised second edition. The author illustrates and explains basic concepts such as Berry phase, scaling, Zitterbewegung, Kubo, Landauer and Mori formalisms in quantum kinetics, chirality, plasmons, commensurate-incommensurate transitions and many others. Open issues and unsolved problems introduce the reader to the latest developments in the field. New achievements and topics presented include the basic concepts of Van der Waals heterostructures, many-body physics of graphene, electronic optics of Dirac electrons, hydrodynamics of electron liquid and the mechanical properties of one atom-thick membranes. Building on an undergraduate-level knowledge of quantum and statistical physics and solid-state theory, this is an important graduate textbook for students in nanoscience, nanotechnology and condensed matter. For physicists and material scientists working in related areas, this is an excellent introduction to the fast-growing field of graphene science.
Book Synopsis 2D Monoelemental Materials (Xenes) and Related Technologies by : Zongyu Huang
Download or read book 2D Monoelemental Materials (Xenes) and Related Technologies written by Zongyu Huang and published by CRC Press. This book was released on 2022-04-19 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Monoelemental 2D materials called Xenes have a graphene-like structure, intra-layer covalent bond, and weak van der Waals forces between layers. Materials composed of different groups of elements have different structures and rich properties, making Xenes materials a potential candidate for the next generation of 2D materials. 2D Monoelemental Materials (Xenes) and Related Technologies: Beyond Graphene describes the structure, properties, and applications of Xenes by classification and section. The first section covers the structure and classification of single-element 2D materials, according to the different main groups of monoelemental materials of different components and includes the properties and applications with detailed description. The second section discusses the structure, properties, and applications of advanced 2D Xenes materials, which are composed of heterogeneous structures, produced by defects, and regulated by the field. Features include: Systematically detailed single element materials according to the main groups of the constituent elements Classification of the most effective and widely studied 2D Xenes materials Expounding upon changes in properties and improvements in applications by different regulation mechanisms Discussion of the significance of 2D single-element materials where structural characteristics are closely combined with different preparation methods and the relevant theoretical properties complement each other with practical applications Aimed at researchers and advanced students in materials science and engineering, this book offers a broad view of current knowledge in the emerging and promising field of 2D monoelemental materials.
Book Synopsis Proximity Enhanced Quantum Spin Hall State in Graphene by :
Download or read book Proximity Enhanced Quantum Spin Hall State in Graphene written by and published by . This book was released on 2015 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Graphene is the first model system of two-dimensional topological insulator (TI), also known as quantum spin Hall (QSH) insulator. The QSH effect in graphene, however, has eluded direct experimental detection because of its extremely small energy gap due to the weak spin-orbit coupling. Here we predict by ab initio calculations a giant (three orders of magnitude) proximity induced enhancement of the TI energy gap in the graphene layer that is sandwiched between thin slabs of Sb2Te3 (or MoTe2). This gap (1.5 meV) is accessible by existing experimental techniques, and it can be further enhanced by tuning the interlayer distance via compression. We reveal by a tight-binding study that the QSH state in graphene is driven by the Kane-Mele interaction in competition with Kekulé deformation and symmetry breaking. As a result, the present work identifies a new family of graphene-based TIs with an observable and controllable bulk energy gap in the graphene layer, thus opening a new avenue for direct verification and exploration of the long-sought QSH effect in graphene.
Book Synopsis Inorganic and Organic Thin Films by : Yu Song
Download or read book Inorganic and Organic Thin Films written by Yu Song and published by John Wiley & Sons. This book was released on 2021-07-19 with total page 771 pages. Available in PDF, EPUB and Kindle. Book excerpt: Learn more about foundational and advanced topics in polymer thin films and coatings besides species with this powerful two-volume resource The two-volume Inorganic and Organic Thin Films: Fundamentals, Fabrication, and Applications delivers a foundational resource for current researchers and commercial users involved in the design and fabrication of thin films. The book offers newcomers to the field a thorough description of new design theory, fabrication methods, and applications of advanced thin films. Readers will discover the physics and chemistry underlying the manufacture of new thin films and coatings in this leading new resource that promises to become a handbook for future applications of the technology. This one-stop reference brings together all important aspects of inorganic and polymeric thin films and coatings, including construction, assembly, deposition, functionality, patterning, and characterization. Explorations of their applications in industries as diverse as information technology, new energy, biomedical engineering, aerospace, and oceanographic engineering round out this fulsome exploration of one of the most exciting and rapidly developing areas of scientific and industrial research today. Readers will also learn from: A comprehensive introduction to the progress of thin films and coatings as well as fundamentals in functional thin films and coatings An exploration of multi-layered magnetic thin films for electron transport control and signal sensing, including giant magnetoresistance, colossal magnetoresistance, tunneling magnetoresistance, and the quantum anomalous Holzer effect An in time summary of high-quality magneto-optics, nanophotonics, spin waves and spintronics using bismuth-substituted iron garnet thin films as examples A thorough discussion of template-assisted fabrication of nanostructure thin films for ultrasensitive detection of chemicals and biomolecules A treatment of biomass derived functional films and coatings Perfect for materials scientists and inorganic chemists, Inorganic and Organic Thin Films will also earn a place in the libraries of solid state physicists and physical chemists working in private industry, as well as polymer and surface chemists who seek to improve their understanding of thin films and coatings.
Book Synopsis Defects in Two-Dimensional Materials by : Rafik Addou
Download or read book Defects in Two-Dimensional Materials written by Rafik Addou and published by Elsevier. This book was released on 2022-02-14 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: Defects in Two-Dimensional Materials addresses the fundamental physics and chemistry of defects in 2D materials and their effects on physical, electrical and optical properties. The book explores 2D materials such as graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMD). This knowledge will enable scientists and engineers to tune 2D materials properties to meet specific application requirements. The book reviews the techniques to characterize 2D material defects and compares the defects present in the various 2D materials (e.g. graphene, h-BN, TMDs, phosphorene, silicene, etc.). As two-dimensional materials research and development is a fast-growing field that could lead to many industrial applications, the primary objective of this book is to review, discuss and present opportunities in controlling defects in these materials to improve device performance in general or use the defects in a controlled way for novel applications. Presents the theory, physics and chemistry of 2D materials Catalogues defects of 2D materials and their impacts on materials properties and performance Reviews methods to characterize, control and engineer defects in 2D materials
Book Synopsis Cluster Superlattices on Hexagonal Boron Nitride and Graphene/ir(111) and Their Embedding with Carbon by : Moritz Will
Download or read book Cluster Superlattices on Hexagonal Boron Nitride and Graphene/ir(111) and Their Embedding with Carbon written by Moritz Will and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ultra-wide Bandgap Semiconductor Materials by : Meiyong Liao
Download or read book Ultra-wide Bandgap Semiconductor Materials written by Meiyong Liao and published by Elsevier. This book was released on 2019-06-18 with total page 503 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ultra-wide Bandgap Semiconductors (UWBG) covers the most recent progress in UWBG materials, including sections on high-Al-content AlGaN, diamond, B-Ga2O3, and boron nitrides. The coverage of these materials is comprehensive, addressing materials growth, physics properties, doping, device design, fabrication and performance. The most relevant and important applications are covered, including power electronics, RF electronics and DUV optoelectronics. There is also a chapter on novel structures based on UWBG, such as the heterojunctions, the low-dimensional structures, and their devices. This book is ideal for materials scientists and engineers in academia and R&D searching for materials superior to silicon carbide and gallium nitride. Provides a one-stop resource on the most promising ultra-wide bandgap semiconducting materials, including high-Al-content AlGaN, diamond, β-Ga2O3, boron nitrides, and low-dimensional materials Presents comprehensive coverage, from materials growth and properties, to device design, fabrication and performance Features the most relevant applications, including power electronics, RF electronics and DUV optoelectronics
