Tuning the Electron-phonon Interaction in Bismuth Selenide (Bi2Se3) Topological Insulator Nanostructures
Author: Christian Ikechukwu Nweze
Publisher:
Published: 2022
Total Pages: 0
ISBN-13:
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Measuring, Interpreting and Translating Electron Quasiparticle - Phonon Interactions on the Surfaces of the Topological Insulators Bismuth Selenide and Bismuth Telluride
Author: Colin Howard
Publisher: Springer
Published: 2018-06-28
Total Pages: 88
ISBN-13: 9783319831206
DOWNLOAD EBOOKThe thesis presents experimental and theoretical results about the surface dynamics and the surface Dirac fermion (DF) spectral function of the strong topological insulators Bi2Te3 and Bi2Se3. The experimental results reveal the presence of a strong Kohn anomaly in the measured surface phonon dispersion of a low-lying optical mode, and the absence of surface Rayleigh acoustic phonons. Fitting the experimental data to theoretical models employing phonon Matsubara functions allowed the extraction of the matrix elements of the coupling Hamiltonian and the modifications to the surface phonon propagator that are encoded in the phonon self-energy. This allowed, for the first time, calculation of phonon mode-specific DF coupling λν(q) from experimental data, with average coupling significantly higher than typical values for metals, underscoring the strong coupling between optical surface phonons and surface DFs in topological insulators. Finally, to connect to experimental results obtained from photoemission spectroscopies, an electronic (DF) Matsubara function was constructed using the determined electron-phonon matrix elements and the optical phonon dispersion. This allowed calculation of the DF spectral function and density of states, allowing for comparison with photoemission and scanning tunneling spectroscopies. The results set the necessary energy resolution and extraction methodology for calculating λ from the DF perspective.
Fano Q-reversal in Topological Insulator Bi2Se3
Author:
Publisher:
Published: 2016
Total Pages: 7
ISBN-13:
DOWNLOAD EBOOKHere, we studied the magneto-optical response of a canonical topological insulator Bi2Se3 with the goal of addressing a controversial issue of electron-phonon coupling. Magnetic-field induced modifications of reflectance are very pronounced in the infrared part of the spectrum, indicating strong electron-phonon coupling. This coupling causes an asymmetric line-shape of the 60 cm-1 phonon mode, and is analyzed within the Fano formalism. The analysis reveals that the Fano asymmetry parameter (q) changes sign when the cyclotron resonance is degenerate with the phonon mode. To the best of our knowledge this is the first example of magnetic field driven q-reversal.
Ultrafast Photoemission Studies of the Topological Insulator Bi2Se3
Author: Jonathan A. Sobota
Publisher:
Published: 2014
Total Pages:
ISBN-13:
DOWNLOAD EBOOKMost macroscopic properties of a material (electrical, thermal, and optical) can be understood on the basis of its band structure and the dynamical behavior of its electrons. However, resolving electron dynamics directly is difficult using conventional techniques because the underlying interactions typically occur on a femtosecond timescale. Ultrafast photoemission spectroscopy is an experimental technique which can probe electronic band structure with femtosecond time resolution. This dissertation presents work using this technique to study dynamic phenomena in the topological insulator Bi2Se3, a fascinating material due to the coexistence of its insulating bulk and metallic surface electronic structures. It will demonstrate three types of novel measurements that can be performed with ultrafast photoemission spectroscopy which are unattainable by other methods: (1) By performing two-photon photoemission (2PPE) spectroscopy, it is possible to resolve unoccupied band structure above the Fermi level. In Bi2Se3 this reveals a second, topologically protected surface state. (2) Time-resolved 2PPE (tr2PPE) is used to record real-time "movies" of the electron relaxation which follows optical excitation. This allows for the identification of intra- and inter- band electron scattering pathways in the material. Temperature-dependent tr2PPE measurements are performed on the conduction band to help understand the role of electron-phonon coupling. A model of fundamental electron-phonon scattering processes is implemented to describe the results. (3) In a time- and angle- resolved photoemission spectroscopy (trARPES) experiment, intense optical excitation is used to drive coherent motion of A1g optical phonon modes in Bi2Se3. These modes lead to periodic binding energy shifts in the bulk conduction band and surface state. A slight red-shift of the phonon frequency is observed in the surface state, which is used to deduce a softening of the phonon due to the abrupt termination of the crystal at its surface.
Electronic Transport in Topological Insulator Nanostructures
Author: Seung Sae Hong
Publisher:
Published: 2013
Total Pages:
ISBN-13:
DOWNLOAD EBOOKTopological insulators are states of quantum matter with an insulating gap in the bulk and gapless surface states. The exotic spin nature of the surface electrons, resulting in topological protection from localization, suggests unconventional applications in electronics as well as fundamental scientific interests. While these exotic states have been investigated via surface-sensitive techniques intensively, electronic transport device, crucial to realize topological electronics, has lagged behind due to material challenges in candidate materials. Topological insulator nanostructure is an attractive candidate for device applications, as the size effect and boundary conditions offer a unique way to enhance / tailor the surface electron transport. In this dissertation, we first describe the design principle of topological insulator nanomaterials, with an emphasis on bismuth selenide. Two major material challenges, dominant bulk electron contribution and low surface mobility due to surface oxidation, are discussed and the solutions via nanomaterial synthesis are achieved. Elemental doping and core-shell heterostructures are developed to suppress bulk carriers and to achieve high surface electron mobility. The high electronic mobility allows us to observe Shubnikov-de Haas oscillations originated from the surface Dirac fermions. In addition to the material development, we also investigate transport properties from helical nature of the surface electrons. 1D modes of surface electrons in bismuth selenide nanowire Aharonov-Bohm interferometers is a unique electronic state providing an opportunity to reveal helical spin nature and topological protection via transport. The helical 1D mode, directly observed near the Dirac point under half magnetic flux quantum, is robust against disorder but fragile against a magnetic field breaking time-reversal-symmetry. The newly discovered 1D helical mode is expected to open a new direction to study topological electronics, as well as future applications.
Advanced Topological Insulators
Author: Huixia Luo
Publisher: John Wiley & Sons
Published: 2019-03-12
Total Pages: 400
ISBN-13: 111940732X
DOWNLOAD EBOOKThis book 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 researchers and graduate students preparing to work in this area, and it will be an essential reference both within and outside the classroom. The book begins with the fundamental description on the topological phases of matter such as one, two- and three-dimensional topological insulators, and methods and tools for topological material's investigations, topological insulators for advanced optoelectronic devices, topological superconductors, saturable absorber and in plasmonic devices. Advanced Topological Insulators provides researchers and graduate students with the physical understanding and mathematical tools needed to embark on research in this rapidly evolving field.
Applications of Laser Ablation
Author: Dongfang Yang
Publisher: BoD – Books on Demand
Published: 2016-12-21
Total Pages: 430
ISBN-13: 9535128116
DOWNLOAD EBOOKLaser ablation refers to the phenomenon in which a low wavelength and short pulse (ns-fs) duration of laser beam irradiates the surface of a target to induce instant local vaporization of the target material generating a plasma plume consisting of photons, electrons, ions, atoms, molecules, clusters, and liquid or solid particles. This book covers various aspects of using laser ablation phenomenon for material processing including laser ablation applied for the deposition of thin films, for the synthesis of nanomaterials, and for the chemical compositional analysis and surface modification of materials. Through the 18 chapters written by experts from international scientific community, the reader will have access to the most recent research and development findings on laser ablation through original research studies and literature reviews.
Collective Excitations in the Antisymmetric Channel of Raman Spectroscopy
Author: Hsiang-Hsi Kung
Publisher:
Published: 2022
Total Pages: 0
ISBN-13: 9783030893330
DOWNLOAD EBOOKThis thesis contains three breakthrough results in condensed matter physics. Firstly, broken reflection symmetry in the hidden-order phase of the heavy-fermion material URu2Si2 is observed for the first time. This represents a significant advance in the understanding of this enigmatic material which has long intrigued the condensed matter community due to its emergent long range order exhibited at low temperatures (the so-called "hidden order"). Secondly and thirdly, a novel collective mode (the chiral spin wave) and a novel composite particle (the chiral exciton) are discovered in the three dimensional topological insulator Bi2Se3. This opens up new avenues of possibility for the use of topological insulators in photonic, optoelectronic, and spintronic devices. These discoveries are facilitated by using low-temperature polarized Raman spectroscopy as a tool for identifying optically excited collective modes in strongly correlated electron systems and three-dimensional topological insulators. .
Materials for Optoelectronics
Author: Maurice Quillec
Publisher: Springer Science & Business Media
Published: 1996-01-31
Total Pages: 404
ISBN-13: 9780792396659
DOWNLOAD EBOOKOptoelectronics ranks one of the highest increasing rates among the different industrial branches. This activity is closely related to devices which are themselves extremely dependent on materials. Indeed, the history of optoelectronic devices has been following closely that of the materials. KLUWER Academic Publishers has thus rightly identified "Materials for Optoelectronics" as a good opportunity for a book in the series entitled "Electronic Materials; Science and Technology". Although a sound background in solid state physics is recommended, the authors have confined their contribution to a graduate student level, and tried to define any concept they use, to render the book as a whole as self-consistent as possible. In the first section the basic aspects are developed. Here, three chapters consider semiconductor materials for optoelectronics under various aspects. Prof. G. E. Stillman begins with an introduction to the field from the point of view of the optoelectronic market. Then he describes how III-V materials, especially the Multi Quantum Structures meet the requirements of optoelectronic functions, including the support of microelectronics for optoelectronic integrated circuits. In chapter 2, Prof.
Topological Insulators
Author: Frank Ortmann
Publisher: John Wiley & Sons
Published: 2015-06-29
Total Pages: 434
ISBN-13: 3527337024
DOWNLOAD EBOOKThere are only few discoveries and new technologies in physical sciences that have the potential to dramatically alter and revolutionize our electronic world. Topological insulators are one of them. The present book for the first time provides a full overview and in-depth knowledge about this hot topic in materials science and condensed matter physics. Techniques such as angle-resolved photoemission spectrometry (ARPES), advanced solid-state Nuclear Magnetic Resonance (NMR) or scanning-tunnel microscopy (STM) together with key principles of topological insulators such as spin-locked electronic states, the Dirac point, quantum Hall effects and Majorana fermions are illuminated in individual chapters and are described in a clear and logical form. Written by an international team of experts, many of them directly involved in the very first discovery of topological insulators, the book provides the readers with the knowledge they need to understand the electronic behavior of these unique materials. Being more than a reference work, this book is essential for newcomers and advanced researchers working in the field of topological insulators.
