Download or read book Theory of Exciton exciton Interactions in Monolayer Transition Metal Dichalcogenides written by Florian Manuel Katsch and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electron Interactions in 2D Materials written by Fengcheng Wu and published by . This book was released on 2016 with total page 236 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents studies of the electron interaction effects in two-dimensional materials. In particular, excitonic effect in transition metal dichalcogenides and quantum Hall effect in graphene have been investigated. The common thread that passes through the two topics is the interplay between electron interactions and spin and valley degrees of freedom. Chapter 1 is a brief introduction to the thesis. Chapter 2 addresses the energy and wave function of excitons in monolayer MoS2. It reveals several interesting features, which can be important for exciton dynamics. Chapter 3 describes a theory of spatially indirect exciton condensates in transition metal dichalcogenide heterostructures. A systematic approach is developed to construct an effective exciton model with exciton-exciton interactions. The effective exciton model provides a useful guidance to construct the condensate phase diagram of excitons with multiple flavors. Chapter 4 identifies an SO(5) symmetry in the quantum Hall effect in graphene. The enlarged SO(5) symmetry unifies the spin antiferromagnetic order and valley XY order. The physics of the SO(5) symmetry is explored using exact diagonalization and low-energy effective theory. Chapter 5 speculates about possible SU(3) and SU(4) singlet fractional quantum Hall states at a filling factor nu=2/3 based on finite-size exact diagonalization study. These singlets are surprising because they are not captured by the composite fermion approach. The shift quantum number and the pair correlation function of the new states are presented.

Download or read book Coherent Light Matter Interactions in Monolayer Transition Metal Dichalcogenides written by Edbert Jarvis Sie and published by Springer. This book was released on 2017-11-11 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents optical methods to split the energy levels of electronic valleys in transition-metal dichalcogenides (TMDs) by means of coherent light-matter interactions. The electronic valleys found in monolayer TMDs such as MoS2, WS2, and WSe2 are among the many novel properties exhibited by semiconductors when thinned down to a few atomic layers, and have have been proposed as a new way to carry information in next generation devices (so-called valleytronics). These valleys are, however, normally locked in the same energy level, which limits their potential use for applications. The author describes experiments performed with a pump-probe technique using transient absorption spectroscopy on MoS2 and WS2. It is demonstrated that hybridizing the electronic valleys with light allows one to optically tune their energy levels in a controllable valley-selective manner. In particular, by using off-resonance circularly polarized light at small detuning, one can tune the energy level of one valley through the optical Stark effect. Also presented within are observations, at larger detuning, of a separate contribution from the so-called Bloch--Siegert effect, a delicate phenomenon that has eluded direct observation in solids. The two effects obey opposite selection rules, enabling one to separate the two effects at two different valleys.

Download or read book Excitonic Linewidth and Coherence Lifetime in Monolayer Transition Metal Dichalcogenides written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Atomically thin transition metal dichalcogenides are direct-gap semiconductors with strong light-matter and Coulomb interactions. The latter accounts for tightly bound excitons, which dominate their optical properties. Besides the optically accessible bright excitons, these systems exhibit a variety of dark excitonic states. They are not visible in the optical spectra, but can strongly influence the coherence lifetime and the linewidth of the emission from bright exciton states. We investigate the microscopic origin of the excitonic coherence lifetime in two representative materials (WS2 and MoSe2) through a study combining microscopic theory with spectroscopic measurements. We also show that the excitonic coherence lifetime is determined by phonon-induced intravalley scattering and intervalley scattering into dark excitonic states. Particularly, we identify exciton relaxation processes involving phonon emission into lower-lying dark states that are operative at all temperatures, in WS2.

Download or read book Quantum Theory of the Optical and Electronic Properties of Semiconductors written by Hartmut Haug and published by World Scientific. This book was released on 1994 with total page 496 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook presents the basic elements needed to understand and engage in research in semiconductor physics. It deals with elementary excitations in bulk and low-dimensional semiconductors, including quantum wells, quantum wires and quantum dots. The basic principles underlying optical nonlinearities are developed, including excitonic and many-body plasma effects. The fundamentals of optical bistability, semiconductor lasers, femtosecond excitation, optical Stark effect, semiconductor photon echo, magneto-optic effects, as well as bulk and quantum-confined Franz-Keldysh effects are covered. The material is presented in sufficient detail for graduate students and researchers who have a general background in quantum mechanics.

Download or read book 2D Materials written by Phaedon Avouris and published by Cambridge University Press. This book was released on 2017-06-29 with total page 521 pages. Available in PDF, EPUB and Kindle. Book excerpt: Learn about the most recent advances in 2D materials with this comprehensive and accessible text. Providing all the necessary materials science and physics background, leading experts discuss the fundamental properties of a wide range of 2D materials, and their potential applications in electronic, optoelectronic and photonic devices. Several important classes of materials are covered, from more established ones such as graphene, hexagonal boron nitride, and transition metal dichalcogenides, to new and emerging materials such as black phosphorus, silicene, and germanene. Readers will gain an in-depth understanding of the electronic structure and optical, thermal, mechanical, vibrational, spin and plasmonic properties of each material, as well as the different techniques that can be used for their synthesis. Presenting a unified perspective on 2D materials, this is an excellent resource for graduate students, researchers and practitioners working in nanotechnology, nanoelectronics, nanophotonics, condensed matter physics, and chemistry.

Download or read book SPIN AND VALLEY DEPENDENT EXCITONS IN ATOMICALLY THIN TRANSITION METAL DICHALCOGENIDES written by Zefang Wang and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Transition metal dichalcogenides (TMDCs) exhibit remarkable electronic properties when thinned down to the monolayer limit. Among them, atomically thin semiconducting TMDCs, such as MoS2, MoSe2, WSe2, etc., attract board interest due to their unique electronic and optoelectronic properties. Electrons in 2D TMDCs acquire not only spin but also valley degree of freedom, and the spin and valley are coupled due to broken inversion symmetry and strong spin-orbit coupling. Opposite valleys are associated with opposite Berry curvature, giving rise to interesting valley physics and valleytronic applications. Another unique aspect of atomically thin TMDCs is strong excitonic effect. Owing to quantum confinement, monolayer semiconducting TMDCs become direct bandgap semiconductor in contrast to indirect bandgap in their bulk counterparts, and the excitonic effect gets greatly boosted due to the reduced dimensionality. Strong excitonic effect gives rise to strong light-matter interaction, making optical spectroscopy a powerful tool to access intriguing spin and valley properties of 2D TMDCs.In this dissertation, we explore the spin and valley dependent properties of monolayer TMDCs with optical and electrical transport techniques with high quality devices. In the first part, we study the electronic band structure in K/K valleys of Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual gate field-effect transistors. Our experiment reveals the distinct spin polarization in the conduction band of these compounds by a systematic study of the doping dependence of A and B excitonic resonances. We obtained conduction band spin splitting delta_c is approximately 40meV for WSe2 and delta_c is approximately -30meV for MoSe2, which are in good agreements with first principle calculations.In the second part, we examined Landau level structure in monolayer WSe2 at the presence of out-of-plane magnetic field. It is proposed by theory that the Berry curvature in valley degree of freedom together with strong spin-orbit interaction can generate unconventional Landau levels under a perpendicular magnetic field. We applied handedness-resolved optical reflection spectroscopy and observed fully valley- and spin-polarized LLs in high quality WSe2 monolayer field-effect transistor and therefore derived LL structure. We also measured a sizeable doping-induced mass renormalization driven by strong Coulomb interactions.In the third part, we continued to explore the strong Coulomb interactions by studying the valley magnetic response in 2D TMDCs. We measured doping dependency of the valley Zeeman splitting of the charged exciton emission in monolayer WSe2 under an out-of-plane magnetic field. A nonlinear valley Zeeman effect correlated with an over fourfold enhancement in the g-factor, is observed. This enhancement occurs when Fermi level crosses the spin-split upper conduction band, corresponding to a change of spin-valley degeneracy from two to four, and can be understood as a consequence of a sharp increase in the exchange interaction when the number of electron species doubles. This interaction-enhanced valley magnetic response suggests 2D TMDCs as a new platform for exploring strongly interacting electron system with multiple internal degrees of freedom.In the final part, a study on interlayer exciton in bilayer WSe2 is presented. Interlayer excitons are sought for creating high exciton density and optoelectronic applications due to their long lifetime. Here we demonstrate highly tunable interlayer excitons by an out-of-plane electric field in bilayer WSe2. Continuous tuning of the exciton dipole from negative to positive orientation has been achieved and a large linear field-induced redshift up to ~100meV has been observed in exciton resonance energy. The Stark effect is accompanied by an enhancement of exciton lifetime by more than two orders of magnitude to >20ns. The exciton density as high as 1.210^11 cm^(2) can be created by moderate continuous-wave optical pumping. Our result has paved the way for realization of degenerate exciton gases in 2D TMDCs.

Download or read book Exciton trion polaritons in Two dimensional Transition metal Dichalcogenides written by Okan Koksal and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation covers a series of experiments that realized, investigated, and controlled exciton-trion-polaritons in transition-metal dichalcogenides (TMDs). First, theoretical and experimental research that led to the established understanding of trions are reviewed. Then, recent theoretical developments that led to a complete reimagining of excitons, trions, and their interactions with photons is discussed. With the theoretical background established, detailed measurements of optical conductivity of TMD MoSe$_2$ are combined with quantitative analysis to determine the nature of strong Coulomb interactions between excitons and bound trions in TMDs. Then, design and simulations of, and measurements on a hybrid photonic-crystal-TMD structure is discussed whereupon remarkable agreement between experiment and theory evidences the existence of coherent exciton-trion-polariton formation. Initial experimental forays into electronic control of the optical properties of this polariton system is then reviewed. In the final chapter of this dissertation, a non-exhaustive investigation of potential device applications based on the understanding of exciton-trion-polaritons is conducted.

Download or read book Probing Light matter Interactions in Atomically Thin 2D Material written by Jonghwan Kim and published by . This book was released on 2015 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recently, atomically thin 2D materials have emerged as a new class of nanomaterial with extraordinary physical properties ranging from semi-metal (graphene), semiconductors (transition metal dichalcogenides) to insulators (hBN). Due to its unusual linear electronic spectrum, graphene has been studied as a platform where exotic quantum mechanical phenomena take place and electro-optical property can be greatly tuned by electrostatic gating. On the other hand, in semiconducting transition metal dichalcogenides (TMD), many body particles such as exciton and trion can be readily accessed even at room temperature due to strong Coulomb interaction. There are further exciting opportunities in heterostructures where layer-layer interaction provides new physics and functionalities. In this thesis, I explore light-matter interaction in 2D materials and their heterostructure with laser spectroscopy techniques. First of all, I study electromagnetic interaction between graphene and optical cavity via Rayleigh scattering spectroscopy. Although light-matter interaction in graphene is extremely strong for atomically thin thickness, overall optical response in macroscopic scale is still limited. Combination of graphene and resonant cavity can amplify the interaction dramatically. Therefore, it is important to understand the electromagnetic interaction between two systems. In this study, I find that the coupling can be explained by real and imaginary part of graphene dielectric constant which affects cavity resonance frequency and quality factor, respectively. In addition to fundamental interest, it also shows that this platform has promising potential for novel sensing application and electro-optical modulator. Secondly, I study valley-selective dipole interaction of exciton states in a monolayer transition metal dichalcogenides. Due to crystal symmetry, an extra degree of freedom, valley state, is available in this system. In analogy to spin state, it is important to understand and manipulate valley state with light. In this study, I demonstrate that valley excitonic states in a monolayer WSe2 can be manipulated by femtosecond pulse with the control of polarization. Ultrafast pump-probe spectroscopy shows that circularly-polarized femtosecond pulse induces valley-selective optical Stark effect which acts as a pseudomagnetic field. This demonstrates efficient and ultrafast control of the valley excitons with optical light, and opens up the possibility to coherent manipulate the valley polarization for quantum information applications. Lastly, I study interlayer interaction in heterostructure of MoS2/WS2 where strong exciton binding energy plays an important role. Simple band theory predicts that a heterostructure of two different semiconducting TMD layers forms type-II heterostructure. However, it is not clear how strong Coulomb interaction plays a role in terms of charge transfer dynamics. In this study, I demonstrate ultrafast charge transfer in MoS2/WS2 via both photoluminescence mapping and femtosecond (fs) pump-probe spectroscopy. Despite large exciton binding energy, hole transfer from the MoS2 layer to the WS2 layer takes place within 50 fs after optical excitation. Such ultrafast charge transfer in van der Waals heterostructures indicates that it can enable novel 2D devices for optoelectronics and light harvesting.

Download or read book Bright and Dark Singlet Excitons Via Linear and Two photon Spectroscopy in Monolayer Transition Metal Dichalcogenides written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We discuss the linear and two-photon spectroscopic selection rules for spin-singlet excitons in monolayer transition-metal dichalcogenides. Our microscopic formalism combines a fully k-dependent few-orbital band structure with a many-body Bethe-Salpeter equation treatment of the electron-hole interaction, using a model dielectric function. We show analytically and numerically that the single-particle, valley-dependent selection rules are preserved in the presence of excitonic effects. Furthermore, we definitively demonstrate that the bright (one-photon allowed) excitons have s-type azimuthal symmetry and that dark p-type excitons can be probed via two-photon spectroscopy. Thus, the screened Coulomb interaction in these materials substantially deviates from the 1/[epsilon]0r form; this breaks the "accidental" angular momentum degeneracy in the exciton spectrum, such that the 2p exciton has a lower energy than the 2s exciton by at least 50 meV. We compare our calculated two-photon absorption spectra to recent experimental measurements.

Download or read book Two Dimensional Transition Metal Dichalcogenides written by Alexander V. Kolobov and published by Springer. This book was released on 2016-07-26 with total page 545 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book summarizes the current status of theoretical and experimental progress in 2 dimensional graphene-like monolayers and few-layers of transition metal dichalcogenides (TMDCs). Semiconducting monolayer TMDCs, due to the presence of a direct gap, significantly extend the potential of low-dimensional nanomaterials for applications in nanoelectronics and nano-optoelectronics as well as flexible nano-electronics with unprecedented possibilities to control the gap by external stimuli. Strong quantum confinement results in extremely high exciton binding energies which forms an interesting platform for both fundamental studies and device applications. Breaking of spatial inversion symmetry in monolayers results in strong spin-valley coupling potentially leading to their use in valleytronics. Starting with the basic chemistry of transition metals, the reader is introduced to the rich field of transition metal dichalcogenides. After a chapter on three dimensional crystals and a description of top-down and bottom-up fabrication methods of few-layer and single layer structures, the fascinating world of two-dimensional TMDCs structures is presented with their unique atomic, electronic, and magnetic properties. The book covers in detail particular features associated with decreased dimensionality such as stability and phase-transitions in monolayers, the appearance of a direct gap, large binding energy of 2D excitons and trions and their dynamics, Raman scattering associated with decreased dimensionality, extraordinarily strong light-matter interaction, layer-dependent photoluminescence properties, new physics associated with the destruction of the spatial inversion symmetry of the bulk phase, spin-orbit and spin-valley couplings. The book concludes with chapters on engineered heterostructures and device applications such as a monolayer MoS2 transistor. Considering the explosive interest in physics and applications of two-dimensional materials, this book is a valuable source of information for material scientists and engineers working in the field as well as for the graduate students majoring in materials science.

Download or read book Quantum Statistics of Nonideal Plasmas written by Dietrich Kremp and published by Springer Science & Business Media. This book was released on 2005-12-11 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the last decade impressive development and signi?cant advance of the physics of nonideal plasmas in astrophysics and in laboratories can be observed, creating new possibilities for experimental research. The enormous progress in laser technology, but also ion beam techniques, has opened new ways for the production and diagnosis of plasmas under extreme conditions, relevant for astrophysics and inertially con?ned fusion, and for the study of laser-matter interaction. In shock wave experiments, the equation of state and further properties of highly compressed plasmas can be investigated. This experimental progress has stimulated the further development of the statistical theory of nonideal plasmas. Many new results for thermodynamic and transport properties, for ionization kinetics, dielectric behavior, for the stopping power, laser-matter interaction, and relaxation processes have been achieved in the last decade. In addition to the powerful methods of quantum statistics and the theory of liquids, numerical simulations like path integral Monte Carlo methods and molecular dynamic simulations have been applied.

Download or read book Excitons in Monolayer Transition Metal Dichalcogenides written by Fabian Stadler and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Two Dimensional Transition Metal Dichalcogenides written by Narayanasamy Sabari Arul and published by Springer. This book was released on 2019-07-30 with total page 355 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents advanced synthesis techniques adopted to fabricate two-dimensional (2D) transition metal dichalcogenides (TMDs) materials with its enhanced properties towards their utilization in various applications such as, energy storage devices, photovoltaics, electrocatalysis, electronic devices, photocatalysts, sensing and biomedical applications. It provides detailed coverage on everything from the synthesis and properties to the applications and future prospects of research in 2D TMD nanomaterials.

Download or read book 2D Excitonic Materials and Devices written by and published by Elsevier. This book was released on 2023-11-23 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconductors and Semimetals series, highlights new advances in the field, with this new volume presenting interesting chapters. Each chapter is written by an international board of authors. - Provides the latest information on cancer research - Offers outstanding and original reviews on a range of cancer research topics - Serves as an indispensable reference for researchers and students alike

Download or read book Exciton Dynamics in Lead Halide Perovskite Nanocrystals written by Bernhard Johann Bohn and published by Springer Nature. This book was released on 2021-05-18 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Less than a decade ago, lead halide perovskite semiconductors caused a sensation: Solar cells exhibiting astonishingly high levels of efficiency. Recently, it became possible to synthesize nanocrystals of this material as well. Interestingly; simply by controlling the size and shape of these crystals, new aspects of this material literally came to light. These nanocrystals have proven to be interesting candidates for light emission. In this thesis, the recombination, dephasing and diffusion of excitons in perovskite nanocrystals is investigated using time-resolved spectroscopy. All these dynamic processes have a direct impact on the light-emitting device performance from a technology point of view. However, most importantly, the insights gained from the measurements allowed the author to modify the nanocrystals such that they emitted with an unprecedented quantum yield in the blue spectral range, resulting in the successful implementation of this material as the active layer in an LED. This represents a technological breakthrough, because efficient perovskite light emitters in this wavelength range did not exist before.

Download or read book Quantum Confined Excitons in 2 Dimensional Materials written by Carmen Palacios-Berraquero and published by Springer. This book was released on 2018-11-02 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the first established experimental results of an emergent field: 2-dimensional materials as platforms for quantum technologies, specifically through the optics of quantum-confined excitons. It also provides an extensive review of the literature from a number of disciplines that informed the research, and introduces the materials of focus – 2d Transition Metal Dichalcogenides (2d-TMDs) – in detail, discussing electronic and chemical structure, excitonic behaviour and response to strain. This is followed by a brief overview of quantum information technologies, including concepts such as single-photon sources and quantum networks. The methods chapter addresses quantum optics techniques and 2d-material processing, while the results section shows the development of a method to deterministically create quantum dots (QDs) in the 2d-TMDs, which can trap single-excitons; the fabrication of atomically thin quantum light-emitting diodes to induce all-electrical single-photon emission from the QDs, and lastly, the use of devices to controllably trap single-spins in the QDs –the first step towards their use as optically-addressable matter qubits.