Superconductivity, Correlation, and Topology in Atomic-thin Quantum Materials PDF Download

Author: Mengke Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Book Description
Atomic thin quantum materials that host exotic quantum phases such as unconventional superconductivity, correlated magnetic insulating, and quantum anomalous Hall insulating states have become a new research frontier due to their intriguing physical phenomena and potential applications that may revolutionize human life. Atomic-thin quantum materials reduce the dimensionality into two, which leads to many unique properties. For example, monolayer or bilayer thin films reduce interlayer coupling compared with their 3D bulk counterparts, thus disentangling the interlayer interaction from interlayer interaction; weakened Coulomb screening at the 2D limit enhances the electron correlations; increased phase fluctuations of the order parameter make it possible for studying quasi-long range order, and quantum confinement from the third dimension may introduce quantum size effect. Thanks to the advancement of material engineering techniques, synthesis or separation of atomic thin quantum materials have become possible and popular. Among these techniques, such as molecular beam epitaxy, physical/chemical vapor deposition, and mechanical exfoliationmolecular beam epitaxy is very powerful due to its precise control of layer thickness and cleanness across a macroscopic wafer scale. Combining molecular beam epitaxy with other in-situ characterization techniques such as scanning tunneling microscopy and double-coil mutual inductance system allows us to design, control, and characterize the atomic thin quantum materials in both microscopic and macroscopic length scales. Here in this dissertation, I first briefly introduce the background motivations of the atomic thin quantum materials in the first chapter. In the second chapter, I cover the research techniques that have been employed during my graduate studies such as molecular beam epitaxy, scanning tunneling microscopy, and double-coil mutual inductance system. The third chapter is devoted to superconductivity in the 2D limit, I use monolayer indium thin film as a platform to discuss how the geometric arrangement of a monolayer indium thin-film affects the superconductivity transition temperature and superfluid density. In the fourth chapter, I use monolayer 1T phase NbSe2 as a material example to discuss the manifestation of strong electron correlation and how it leads to magnetic charge-transfer insulators in its charge density wave phase. I also discuss the interplay of local magnetic moments with metallic/superconducting states, which lead to Kondo resonances and Yu-Shiba-Rusinov-like bound states. The fifth chapter focuses on the concept of band topology and its accompanied surface states. I use intrinsic magnetic topological insulator MnBi2Te4 as a material platform to discuss the interplay of the Dirac mass gap with magnetism and its theoretical understanding. Finally, I make some concluding remarks, including so far confronted obstacles in these topics, and comment on the further steps to make for future advancement

Author: Vladyslav Kozii
Publisher:
ISBN:
Category :
Languages : en
Pages : 342

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Book Description
The theory of superconductivity developed by Bardeen, Cooper, and Schrieffer has proven to correctly describe a wide class of metals, where the effective attraction between electrons is mediated by phonons. Despite huge success, this theory fails to explain certain types of superconductivity, which includes but not limited to topological superconductivity and superconductivity in systems with low carrier density. We study new exciting properties of these materials and discuss possible microscopic mechanisms for exotic superconductivity. In Part I of this thesis, we explore the properties of two-component superconductors with strong spin-orbit coupling. Our study is motivated by the experiments on a topological superconductor candidate material, Bi2Se3 doped with Cu, Sn, or Nb atoms. Generally, superconductivity in such systems comes in two flavors: nematic, which breaks rotational symmetry of the crystal, and time-reversal breaking chiral. We study the relative energetics and different features specific to each of these flavors. We find that, in three dimensions, the nematic superconductors generically possess full pairing gap on the Fermi surface, thus representing a solid-state realization of a time-reversal-invariant topological superconductor. On the contrary, chiral superconductors host non-degenerate point nodes on the Fermi surface and represent the superconducting analog of topological Weyl semimetals; the low-energy excitations in these materials are itinerant Majorana fermions. In Part II, we suggest possible microscopic mechanisms for unconventional superconductivity. We show that strong fluctuations of the inversion-breaking order parameter induce instability in an odd-parity superconducting channel, suggesting a route towards topological superconductivity. Using bosonization, we generalize this result to one-dimensional systems. We apply our findings to study superconductivity in three-dimensional Dirac materials with extremely low density of carriers. Finally, we discuss the mechanism for nematic superconductivity from density wave fluctuations in two-dimensional systems, with possible application to twisted bilayer graphene. The results presented in this thesis are mainly based on Refs. [1, 2, 3, 4, 5, 6, 7].

Author: Yingming Xie
Publisher:
ISBN:
Category : Condensed matter
Languages : en
Pages : 150

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Author: B. Andrei Bernevig
Publisher: Princeton University Press
ISBN: 1400846730
Category : Science
Languages : en
Pages : 264

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Book Description
This graduate-level textbook is the first pedagogical synthesis of the field of topological insulators and superconductors, one of the most exciting areas of research in condensed matter physics. Presenting the latest developments, while providing all the calculations necessary for a self-contained and complete description of the discipline, it is ideal for graduate students and researchers preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with simple concepts such as Berry phases, Dirac fermions, Hall conductance and its link to topology, and the Hofstadter problem of lattice electrons in a magnetic field. It moves on to explain topological phases of matter such as Chern insulators, two- and three-dimensional topological insulators, and Majorana p-wave wires. Additionally, the book covers zero modes on vortices in topological superconductors, time-reversal topological superconductors, and topological responses/field theory and topological indices. The book also analyzes recent topics in condensed matter theory and concludes by surveying active subfields of research such as insulators with point-group symmetries and the stability of topological semimetals. Problems at the end of each chapter offer opportunities to test knowledge and engage with frontier research issues. Topological Insulators and Topological Superconductors will provide graduate students and researchers with the physical understanding and mathematical tools needed to embark on research in this rapidly evolving field.

Author: David A. Cardwell
Publisher: CRC Press
ISBN: 1000600076
Category : Science
Languages : en
Pages : 1088

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Book Description
This is the first of three volumes of the extensively revised and updated second edition of the Handbook of Superconductivity. The past twenty years have seen rapid progress in superconducting materials, which exhibit one of the most remarkable physical states of matter ever to be discovered. Superconductivity brings quantum mechanics to the scale of the everyday world where a single, coherent quantum state may extend over a distance of metres, or even kilometres, depending on the size of a coil or length of superconducting wire. Viable applications of superconductors rely fundamentally on an understanding of this intriguing phenomena and the availability of a range of materials with bespoke properties to meet practical needs. This first volume covers the fundamentals of superconductivity and the various classes of superconducting materials, which sets the context and background for Volumes 2 and 3. Key Features: Covers the depth and breadth of the field Includes contributions from leading academics and industry professionals across the world Provides hands-on guidance to the manufacturing and processing technologies A comprehensive reference, this handbook is suitable for both graduate students and practitioners in experimental physics, materials science and multiple engineering disciplines, including electronic and electrical, chemical, mechanical, metallurgy and others.

Author: Daisuke Ogura
Publisher: Springer Nature
ISBN: 9811506671
Category : Technology & Engineering
Languages : en
Pages : 122

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Book Description
This book deals with the study of superconductivity in systems with coexisting wide and narrow bands. It has been previously suggested that superconductivity can be enhanced in systems with coexisting wide and narrow bands when the Fermi level is near the narrow band edge. In this book, the authors study two problems concerning this mechanism in order to: (a) provide a systematic understanding of the role of strong electron correlation effects, and (b) propose a realistic candidate material which meets the ideal criteria for high-Tc superconductivity. Regarding the role of strong correlation effects, the FLEX+DMFT method is adopted. Based on systematic calculations, the pairing mechanism is found to be indeed valid even when the strong correlation effect is considered within the formalism. In the second half of the book, the authors propose a feasible candidate material by introducing the concept of the “hidden ladder” electronic structure, arising from the combination of the bilayer lattice structure and the anisotropic orbitals of the electrons. As such, the book contributes a valuable theoretical guiding principle for seeking unknown high-Tc superconductors.

Author: Satoru Ichinokura
Publisher: Springer
ISBN: 9811068534
Category : Science
Languages : en
Pages : 135

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Book Description
This thesis presents first observations of superconductivity in one- or two-atomic-scale thin layer materials. The thesis begins with a historical overview of superconductivity and the electronic structure of two-dimensional materials, and mentions that these key ingredients lead to the possibility of the two-dimensional superconductor with high phase-transition temperature and critical magnetic field. Thereafter, the thesis moves its focus onto the implemented experiments, in which mainly two different materials thallium-deposited silicon surfaces and metal-intercalated bilayer graphenes, are used. The study of the first material is the first experimental demonstration of both a gigantic Rashba effect and superconductivity in the materials supposed to be superconductors without spatial inversion symmetry. The study of the latter material is relevant to superconductivity in a bilayer graphene, which was a big experimental challenge for a decade, and has been first achieved by the author. The description of the generic and innovative measurement technique, highly effective in probing electric resistivity of ultra-thin materials unstable in an ambient environment, makes this thesis a valuable source for researchers not only in surface physics but also in nano-materials science and other condensed-matter physics.

Author: Mahmoud Lababidi
Publisher:
ISBN:
Category : Energy-band theory of solids
Languages : en
Pages : 87

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Book Description
Topological insulators (TI), such as Bi2Se3, are a new class of quantum materials discovered recently. They are insulating in the bulk but can conduct on the surfaces. The robust surface states of three-dimensional strong TIs form a unique two-dimensional system of massless electrons, known as a helical metal, with a linear energy-momentum dispersion and spin-momentum locking. While these surface modes alone have spurred great interest, their interaction with superconductors (S) in close proximity has opened up opportunities to engineer topological superconductivity using TI-S heterostructures. This thesis is a microscopic, self-consistent theoretical investigation of the interplay between TI and superconductors. Three types of TI-based heterostructures with increasing complexity are studied in detail. We first present a detailed study of the coupling between a metal and a topological insulator. We compute the spin-active scattering matrix for electrons coming from the metal incident on the metal-TI interface. We find that there exists a critical incident angle, where perfect spin-flip occurs as the incoming electron is reflected. We discuss the origin of this phenomena and its potential implications in spintronics. We then compute the local spectrum at the metal-TI interface, and examine its evolution from the tunneling limit (bad contact) to the strong coupling limit (good contact). The calculations are done using two complementary approaches; in a continuum model based on a k·p Hamiltonian a wave function matching approach is taken and the lattice model requires the use of lattice Green's functions. The study of metal-TI interface lays the foundation for our subsequent theory of S-TI interface. Next we carry out microscopic, self-consistent calculations of the superconducting order parameter and pairing correlations near a S-TI interface, where S is an s-wave superconductor. We discuss the suppression of the order parameter by the topological insulator and show that triplet pairing correlations are induced by spin-flip scattering at the interface. We verify that the interface spectrum at sub-gap energies is well described by the Fu-Kane model even for strongly coupled S and TI. These sub-gap modes are interface states with spectral weight penetrating well into the superconductor. We extract the phenomenological parameters of the phenomenological Fu-Kane model from our microscopic calculations, and find they are strongly renormalized from the bulk material parameters. Building upon such understanding of single TI-S interface, we move on to examine a TI surface in contact with two superconductors with a phase bias, namely a Josephson junction patterned on the TI surface and mediated by the helical metal. A short Josephson junction of this kind at a phase bias of [pi] is known to give rise to exotic quasiparticle excitations known as Majorana fermions with a linear dispersion, E ~ k. Our self-consistent calculation of the Andreev bound states spectrum reveals, for the first time, a new regime with very different physics in these devices. We show that the subgap spectrum becomes nearly flat at zero energy when the chemical potential is sufficiently away from the Dirac point. The flat dispersion is well approximated by E ~ k[superscript N], where N scales with the chemical potential. We find a similar linear-to-flat dispersion evolution also occurs for the subgap spectrum of a periodic superconducting proximity structure, such as a TI surface in contact with a striped superconductor. The systematic microscopic study of TI-S heterostructures helps interpret the data from ongoing experiments on these structures. The formalism developed also forms the basis for subsequent investigation of more complicated layered materials such as the periodic array of magnetically doped TI and S which is argued to give rise to an exotic topological superconductor known as Weyl superconductor.

Author: Richard E. Prange
Publisher: Springer Science & Business Media
ISBN: 146123350X
Category : Technology & Engineering
Languages : en
Pages : 487

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Book Description
After a foreword by Klaus von Klitzing, the first chapters of this book discuss the prehistory and the theoretical basis as well as the implications of the discovery of the Quantum Hall effect on superconductivity, superfluidity, and metrology, including experimentation. The second half of this volume is concerned with the theory of and experiments on the many body problem posed by fractional effect. Specific unsolved problems are mentioned throughout the book and a summary is made in the final chapter. The quantum Hall effect was discovered on about the hundredth anniversary of Hall's original work, and the finding was announced in 1980 by von Klitzing, Dorda and Pepper. Klaus von KIitzing was awarded the 1985 Nobel prize in physics for this discovery.

Author: Ulrich Schollwöck
Publisher: Springer
ISBN: 3540400664
Category : Science
Languages : en
Pages : 488

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Book Description
Closing a gap in the literature, this volume is intended both as an introductory text at postgraduate level and as a modern, comprehensive reference for researchers in the field. Provides a full working description of the main fundamental tools in the theorists toolbox which have proven themselves on the field of quantum magnetism in recent years. Concludes by focusing on the most important cuurent materials form an experimental viewpoint, thus linking back to the initial theoretical concepts.