The Paired Electron Crystal Exotic Phases And Phase Transitions In Strongly Correlated Electron Systems

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The Paired Electron Crystal, Exotic Phases and Phase Transitions in Strongly Correlated Electron Systems

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (86 download)

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Book Synopsis The Paired Electron Crystal, Exotic Phases and Phase Transitions in Strongly Correlated Electron Systems by :

Download or read book The Paired Electron Crystal, Exotic Phases and Phase Transitions in Strongly Correlated Electron Systems written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Almost a century after its discovery, superconductivity (SC) is still the most challenging and fascinating topic in condensed matter physics. Organic superconductors show exotic phases and phase transitions with a change in temperature or pressure. In this dissertation, we studied the phases and phase-transitions in one-dimensional (1D) and two-dimensional (2D) organic materials. This dissertation itself is a group of three sub-projects. In project (i), we studied the properties of a novel state "paired electron crystal" (PEC) in the quarterfilled Hubbard model to understand the phases and properties of 2D organic materials. We also studied the effects of charge and spin frustration on the 2D strongly correlated quarterfilled band. Our conclusions are based on exact diagonalization (ED) studies that include electron-electron and adiabatic electron-phonon interactions. For moderate to strong frustration, the dominant phase is a novel spin-singlet PEC. We discuss the implications of the PEC concept for understanding several classes of quarter-filled band materials that display unconventional superconductivity. In project (ii), we studied the thermodynamics of a zigzag ladder model, applicable to quasi-1D organic materials. Using the quantum Monte Carlo (QMC) method, we studied the thermodynamics of charge ordering in quarter-filled quasi-1D organic charge transfer solids (CTS). Previous theoretical studies on these CTS have focused on ground state properties or purely 1D systems. In the zigzag ladder, no separate high-temperature ordering is expected; instead the ladder is metallic at high temperature, and as temperature decreases, a single transition to the PEC state with a spin-gap takes place. In project (iii), we studied superconducting pairing correlation and metal-insulator transitions in the half-filled Hubbard model. We employed the Hubbard model and used the path integral renormalization group (PIRG) method for this study. Antiferromagneticmediated SC was suggested for small to large frustration in anisotropic triangular lattices. Previous work on the half-filled Hubbard model using the ED method was successful in showing the absence of d-wave SC on a small anisotropic triangular lattice. We extended this study to larger lattices to investigate the existence of long-range order of superconducting pair-pair correlations. We also show the absence of d-wave SC in this model on larger lattices.

Phases and Phase Transitions of Strongly Correlated Electron Systems

Author : Pouyan Ghaemi Mohammadi
Publisher :
ISBN 13 :
Total Pages : 348 pages
Book Rating : 4.:/5 (318 download)

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Book Synopsis Phases and Phase Transitions of Strongly Correlated Electron Systems by : Pouyan Ghaemi Mohammadi

Download or read book Phases and Phase Transitions of Strongly Correlated Electron Systems written by Pouyan Ghaemi Mohammadi and published by . This book was released on 2008 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: Different experiments on strongly correlated materials have shown phenomena which are not consistent with our conventional understandings. We still do not have a general framework to explain these properties. Developing such a general framework is much beyond the scope of this thesis, but here we try to address some of challenges in simpler models that are more tractable. In correlated metals it appears as strong correlations have different effect on different parts of fermi surface. Perhaps most striking example of this is normal state of optimally doped cuprates; the quasiparticle peaks on the nominal fermi surface do not appear uniformly. We try to track such phenomena in heavy fermion systems, which are correlated fermi liquids. In these systems, a lattice of localized electrons in f or d orbitals is coupled to the conduction electrons through an antiferromagnetic coupling. Singlets are formed between localized and conduction electrons. This singlet naturally have non-zero internal angular momentum. This nontrivial structure leads to anisotropic effect of strong correlations. Internal structure of Kondo singlet can also lead to quantum Hall effect in Kondo insulator, and formation of isolated points on the fermi surface with fractionalized quasiparticles. In the second part we study a phase transition in Heisenberg model between two insulating phases, Neel ordered and certain spin liquid state, popular in theories of the cuprates. The existence of such a transition has a number of interesting implications for spin liquid based approaches to the underdoped cuprates and clarifies existing ideas for incorporating antiferromagnetic long range order into such a spin liquid based approach. This transition might also be enlightening, despite fundamental differences, for the heavy fermion critical points where a second order transition between the heavy fermion phase and a metallic phase with magnetic antiferromagnetic order is observed.

Competing Phases and Basic Mechanisms in Strongly-interacting Electron Systems

Author :
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (871 download)

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Book Synopsis Competing Phases and Basic Mechanisms in Strongly-interacting Electron Systems by :

Download or read book Competing Phases and Basic Mechanisms in Strongly-interacting Electron Systems written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The goal of this work was to continue the effort to develop numerical tools in order to understand the properties of strongly-correlated electron materials. Towards this goal, they developed new stochastic series Monte Carlo techniques to study the phases of a two-dimensional quantum XY model with ring exchange in an external magnetic field. They determined the zero-temperature phase diagram of this model and found two quantum phase transitions. The first was between an XY-ordered phase and a striped valence-bond phase. The second was between the valence-bond phase and a staggered Neel antiferromagnetic phase. With the external field as an additional control parameter they were able to conclude that this system did not show a quantum spin liquid phase. They extended the study of the Xy model with ring exchange to study its behavior in the 3 dimensions. They find that in three dimensions, the superfluid phase persists to asymptotically large values of the ring exchange K. they do find exotic fractionalized phases in three dimensions. The role of the electron-phonon coupling in the cuprates remains open. They have studied the effect of an onsite Hubbard U Coulomb interaction on the electron-phonon vertex. They found that at strong coupling, Coulomb interaction caused the electron-phonon interaction to be suppressed at large momentum transfers leading to an effective peaking of the interaction in the forward direction while for weaker values of U, the electron-phonon interaction was simply suppressed at all q values. This behavior could favor d-wave pairing, although the effective pairing strength of the phonons remains weak in this model. The dynamics of the pairing interaction is reflected in the frequency dependence of the gap. They have used exact diagonalization to study the frequency dependence of the gap for a two-leg t-J ladder. They were able to determine both the real and imaginary parts of the gap. The key observation was that the weight of the imaginary part was sufficient to account for most all of Re[Delta] (k, [omega] = 0), implying that the dynamics of the interaction is not set by the Mott-Hubbard gap (which is infinite for the t-J model).

Exotic Phases and Quantum Criticality in Gapless Correlated Electron Systems

Author : David Fabian Mross
Publisher :
ISBN 13 :
Total Pages : 219 pages
Book Rating : 4.:/5 (867 download)

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Book Synopsis Exotic Phases and Quantum Criticality in Gapless Correlated Electron Systems by : David Fabian Mross

Download or read book Exotic Phases and Quantum Criticality in Gapless Correlated Electron Systems written by David Fabian Mross and published by . This book was released on 2013 with total page 219 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, I theoretically studied exotic phases of matter than arise due to strong interactions between electrons in three different scenarios. Firstly, at a stripe melting phase transition, which may be relevant for the high temperature superconductors, where we propose a specific type of transition which produces critical exponents agreeing with neutron scattering experiments on LSCO. Secondly, for a Pomeranchuk transition where an electronic nematic order parameter develops we present a controlled expansion within which the physics of such a transition, and of the related problem of fermions coupled to a gauge field, can be addressed. Thirdly, in a quantum spin liquid phase that is likely to be realized in certain organic Mott insulators. Here we show how such a phase can be accessed from a low energy description of a metal, without resorting to slave-particle constructions. Methodologically, the work in this thesis relies on field theoretical methods such as the renormalization group, the large-N and related expansions, dualities, bosonization and slave-particle constructions.

Exotic Quantum Phases and Phase Transitions of Strongly Interacting Electrons in Low-Dimensional Systems

Author : Ryan V. Mishmash
Publisher :
ISBN 13 : 9781321202519
Total Pages : 190 pages
Book Rating : 4.2/5 (25 download)

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Book Synopsis Exotic Quantum Phases and Phase Transitions of Strongly Interacting Electrons in Low-Dimensional Systems by : Ryan V. Mishmash

Download or read book Exotic Quantum Phases and Phase Transitions of Strongly Interacting Electrons in Low-Dimensional Systems written by Ryan V. Mishmash and published by . This book was released on 2014 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Finally, working in two dimensions directly, we propose a new slave-particle theory which explains in a universal way many of the intriguing experimental results of the triangular lattice organic spin liquid candidates kappa-(BEDT-TTF) 2Cu2(CN)3 and EtMe3Sb[Pd(dmit) 2]2. With use of large-scale variational Monte Carlo calculations, we show that this new state has very competitive trial energy in an effective spin model thought to describe the essential features of the real materials.

Exploring Electron-electron and Electron-phonon Interactions in Strongly Interacting Quantum Systems

Author : Bo Xiao
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.6/5 (912 download)

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Book Synopsis Exploring Electron-electron and Electron-phonon Interactions in Strongly Interacting Quantum Systems by : Bo Xiao

Download or read book Exploring Electron-electron and Electron-phonon Interactions in Strongly Interacting Quantum Systems written by Bo Xiao and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electron-electron and electron-phonon interactions play fundamental roles in condensed matter physics. Strong correlations among electrons and between electrons and phonons lead to beautiful emergent phenomena both in materials and in the models used to describe them. Unfortunately, the complexity induced from the combination of interactions and large numbers of degrees of freedom makes analytically solving these models very difficult, even when greatly simplified. As a consequence, many important questions in many-body physics remain open. For example, the discoveries of charge density wave (CDW) in the pseudogap phase of the unconventional high-temperature cuprate superconductors motivate on-going research on electron-phonon interactions and its effects on the off-diagonal long-range order (ODLRO). In conventional superconductors, the attractive interaction between electrons which is mediated by the electron-phonon interaction is essential for the formation of Cooper pairs. However, if the electron-phonon interaction is sufficiently strong, charge order emerges near commensurate filling to compete with superconductivity. In this thesis, we use a combination of numerical and analytical methods to understand this sort of interplay between different types of order in the microscopic and macroscopic behavior of many-body systems. In Chapter 1, we introduce the Hubbard and Holstein Hamiltonians and the some of the exotic phases and phase transitions which they describe. We also build up some of the connections between numerical solutions of these models and experimental results for superconducting, charge, and spin order. In Chapter 2 and 3, we set up the frameworks of quantum Monte Carlo (QMC) algorithms and machine learning (ML) methods. We show how to translate a quantum-mechanical problem into an algorithm with analytical analysis encoded in it, which can be widely applied to various models and physics. In Chapter 4 and 5, we quantitatively determine the phase diagrams of one dimensional electron-phonon models where electrons have a long-range coupling to phonons as well as repulsive electron-electron interactions. We analyze the resulting metallic, Mott insulator, Peierls insulator phases, as well as the phase separation which we show often arises from momentum-dependent electron-phonon coupling. Although much work has been done on the extended Hubbard model, our research on including electron-phonon interactions pushes the field in a new direction. In Chapter 6, we describe the first study of the interplay between electron-phonon interaction and the effects of randomness. Our central result is a somewhat unexpected one: the suppression of the charge density wave correlations in the half-filled Holstein model by disorder can stabilize a superconducting phase. In Chapter 7, we use QMC and cutting-edge ML methods to identify phase transitions involving 'off-diagonal' order parameters using 'diagonal' order parameter descriptors. Our study has implications for the exploration of strong correlations using quantum gas microscopy (QGM). Chapter 8 summarizes some of the key results of this thesis, and points areas of investigation which would be important to pursue further. The material presented in Chapters 3, 4 and 5 of this dissertation is based on two published articles in Physical Review B, references [1, 2], and one manuscript which has been submitted and is under review at Physical Review Letters, reference [3]. Chapter 7 is based on reference [4], which is in preparation.

Electron-Electron Interactions in Two-Dimensional Spin-Orbit Coupled Systems

Author : Ali Ashrafi
Publisher :
ISBN 13 :
Total Pages : 86 pages
Book Rating : 4.:/5 (885 download)

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Book Synopsis Electron-Electron Interactions in Two-Dimensional Spin-Orbit Coupled Systems by : Ali Ashrafi

Download or read book Electron-Electron Interactions in Two-Dimensional Spin-Orbit Coupled Systems written by Ali Ashrafi and published by . This book was released on 2013 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: The work presented in this dissertation attempts to bring together two very active research venues in condensed matter physics. The first one is the field of strongly correlated electron systems and quantum phase transitions in itinerant electron systems. The second one is the field of semiconductor spintronics and quantum computation, in particular, a subfield of the latter that studies coherence in semiconductor spin qubits. To explore interesting overlap regions between these two venues, we extend the Landau's Fermi liquid (FL) theory to include a spin-orbit (SO) coupling. It is shown that although "charge-part" quantities, such as the charge susceptibility and effective mass, are determined solely by the quasi-particles, "spin-part" quantities, such as the spin susceptibility, have contributions from the damped states in between the two spin-split Fermi surfaces. Properties of such FLs are discussed in detail. We also study the linear response of an SU(2) symmetric FL to an SO perturbation and predict new types of collective modes in FLs with SO coupling: chiral spin-waves. We find the equations of motion for these modes and propose an experimental setup suitable to observe them.

Strongly Correlated Electron Systems Ii - Proceedings Of The Adriatico Conference And Miniworkshop

Author : G Baskaran
Publisher : World Scientific
ISBN 13 : 9814569348
Total Pages : 444 pages
Book Rating : 4.8/5 (145 download)

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Book Synopsis Strongly Correlated Electron Systems Ii - Proceedings Of The Adriatico Conference And Miniworkshop by : G Baskaran

Download or read book Strongly Correlated Electron Systems Ii - Proceedings Of The Adriatico Conference And Miniworkshop written by G Baskaran and published by World Scientific. This book was released on 1991-02-28 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is the second in a series of miniworkshops and Adriatico conferences devoted to the exciting field of strongly correlated electron systems including quantum Hall effect, metal insulator transition, heavy fermions and high Tc superconductivity. In spite of enormous efforts made by physicists worldwide to solve these difficult problems, many important issues are still widely open and this topic remains the most active field in condensed matter physics. The review talks and reports on original research given by the experts in the field represent a state-of-the-art summary of this fast-moving field.

Electronic Phase Transitions

Author : Yu.V. Kopaev
Publisher : Elsevier
ISBN 13 : 0444600396
Total Pages : 353 pages
Book Rating : 4.4/5 (446 download)

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Book Synopsis Electronic Phase Transitions by : Yu.V. Kopaev

Download or read book Electronic Phase Transitions written by Yu.V. Kopaev and published by Elsevier. This book was released on 2012-12-02 with total page 353 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle electronic structure calculations and critical phenomena - has given rise to impressive new insights. Clearly, there is more and more need for accurate, stable numerical simulations of models of interacting electrons, presently discussed with great vigor in connection with high-Tc superconductors where the superconducting transition is close to a magnetic transition, i.e. an antiferromagnetic spin structure. These topics and others are discussed and reviewed by leading experts in the field.

Phase Transitions and Crystal Symmetry

Author : Yurii Aleksandrovich Izyumov
Publisher : Springer Science & Business Media
ISBN 13 : 9400919204
Total Pages : 462 pages
Book Rating : 4.4/5 (9 download)

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Book Synopsis Phase Transitions and Crystal Symmetry by : Yurii Aleksandrovich Izyumov

Download or read book Phase Transitions and Crystal Symmetry written by Yurii Aleksandrovich Izyumov and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 462 pages. Available in PDF, EPUB and Kindle. Book excerpt: About half a century ago Landau formulated the central principles of the phe nomenological second-order phase transition theory which is based on the idea of spontaneous symmetry breaking at phase transition. By means of this ap proach it has been possible to treat phase transitions of different nature in altogether distinct systems from a unified viewpoint, to embrace the aforemen tioned transitions by a unified body of mathematics and to show that, in a certain sense, physical systems in the vicinity of second-order phase transitions exhibit universal behavior. For several decades the Landau method has been extensively used to an alyze specific phase transitions in systems and has been providing a basis for interpreting experimental data on the behavior of physical characteristics near the phase transition, including the behavior of these characteristics in systems subject to various external effects such as pressure, electric and magnetic fields, deformation, etc. The symmetry aspects of Landau's theory are perhaps most effective in analyzing phase transitions in crystals because the relevant body of mathemat ics for this symmetry, namely, the crystal space group representation, has been worked out in great detail. Since particular phase transitions in crystals often call for a subtle symmetry analysis, the Landau method has been continually refined and developed over the past ten or fifteen years.

Two-Particle Excitations in Strongly Correlated Electron Systems

Author : Sebastian Schmitt
Publisher :
ISBN 13 : 9783838107967
Total Pages : 0 pages
Book Rating : 4.1/5 (79 download)

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Book Synopsis Two-Particle Excitations in Strongly Correlated Electron Systems by : Sebastian Schmitt

Download or read book Two-Particle Excitations in Strongly Correlated Electron Systems written by Sebastian Schmitt and published by . This book was released on 2009-06-05 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Strongly Correlated Electrons in Two Dimensions

Author : Sergey Kravchenko
Publisher : Jenny Stanford Publishing
ISBN 13 : 9789814745376
Total Pages : 0 pages
Book Rating : 4.7/5 (453 download)

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Book Synopsis Strongly Correlated Electrons in Two Dimensions by : Sergey Kravchenko

Download or read book Strongly Correlated Electrons in Two Dimensions written by Sergey Kravchenko and published by Jenny Stanford Publishing. This book was released on 2017-02-13 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last three decades, strongly correlated 2D electron systems have garnered scientific interest because of their unique and often unpredictable properties. One of the many examples is the metallic state and the metal-insulator transition discovered in 2D semiconductors--phenomena that cannot occur in non-interacting systems. This discovery is important in modern condensed matter physics, for which theoretical methods are still poorly developed. This book details cutting-edge research in experimental and theoretical physics of strongly correlated electron systems by leading researchers in the field.

Quantum Phase Transitions in Correlated Electron Systems

Author : Hilbert von Löhneysen
Publisher :
ISBN 13 :
Total Pages : 177 pages
Book Rating : 4.:/5 (92 download)

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Book Synopsis Quantum Phase Transitions in Correlated Electron Systems by : Hilbert von Löhneysen

Download or read book Quantum Phase Transitions in Correlated Electron Systems written by Hilbert von Löhneysen and published by . This book was released on 2015 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Correlated Many-electron Phenomena in the Quantum Hall Regime

Author : Gerardo Gamez-Corrales
Publisher :
ISBN 13 :
Total Pages : 107 pages
Book Rating : 4.:/5 (222 download)

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Book Synopsis Correlated Many-electron Phenomena in the Quantum Hall Regime by : Gerardo Gamez-Corrales

Download or read book Correlated Many-electron Phenomena in the Quantum Hall Regime written by Gerardo Gamez-Corrales and published by . This book was released on 2007 with total page 107 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Orbital-order Phase Transition and Non-adiabatic Quantum-classical Dynamics in Strongly Coupled Electron-phonon Systems

Author : Michael Wilhelm ten Brink
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (138 download)

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Book Synopsis Orbital-order Phase Transition and Non-adiabatic Quantum-classical Dynamics in Strongly Coupled Electron-phonon Systems by : Michael Wilhelm ten Brink

Download or read book Orbital-order Phase Transition and Non-adiabatic Quantum-classical Dynamics in Strongly Coupled Electron-phonon Systems written by Michael Wilhelm ten Brink and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis contributes to the investigation of solid-state systems with a strong coupling between electrons and the surrounding atomic lattice (phonons). One focus point of the thesis is the material class of $Pr_{1-x}Ca_{x}MnO_3$ (PCMO), a strongly correlated perovskite manganese oxide, which shows a photovoltaic effect that is highly influenced by the electron-phonon interactions present in the material. We use a theoretical model including electron, phonon, and spin degrees of freedom in a combined quantum-mechanical/classical description to investigate ground-state ordered phases and t...

Strongly Correlated Electron Systems Under High Pressure: Structural, Magnetic, and Superconducting Phase Transitions

Author : Heribert Wilhelm
Publisher :
ISBN 13 :
Total Pages : 86 pages
Book Rating : 4.:/5 (315 download)

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Book Synopsis Strongly Correlated Electron Systems Under High Pressure: Structural, Magnetic, and Superconducting Phase Transitions by : Heribert Wilhelm

Download or read book Strongly Correlated Electron Systems Under High Pressure: Structural, Magnetic, and Superconducting Phase Transitions written by Heribert Wilhelm and published by . This book was released on 1999 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Non-equilibrium Phase Transformations in Charge-density Wave and Strongly Correlated Systems Studied by Coherent Femtosecond Electron Diffraction

$Download Non-equilibrium Phase Transformations in Charge-density Wave and Strongly Correlated Systems Studied by Coherent Femtosecond Electron Diffraction PDF Online Free$

Author : Faran Zhou
Publisher :
ISBN 13 : 9781392687604
Total Pages : 208 pages
Book Rating : 4.6/5 (876 download)

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Book Synopsis Non-equilibrium Phase Transformations in Charge-density Wave and Strongly Correlated Systems Studied by Coherent Femtosecond Electron Diffraction by : Faran Zhou

Download or read book Non-equilibrium Phase Transformations in Charge-density Wave and Strongly Correlated Systems Studied by Coherent Femtosecond Electron Diffraction written by Faran Zhou and published by . This book was released on 2019 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: By photo-exciting electrons in a material causing subsequent electron-electron and electron-phonon interactions, an energy landscape is created that is very different from that in thermal equilibrium. This distinction sets the baseline that photo-induced phase transitions (PIPT) could go through very different pathways compared with the thermally-induced phase transitions in equilibrium. This opens up a new dimension for complex materials research in non-equilibrium with ultrafast tools. In recent years, with the discovery of photo-induced superconductivity (SC) and other hidden quantum states, the study of these metastable and hidden phases in quantum materials has drawn intense interest in the ultrafast community.With femtosecond electron diffraction, we have observed intriguing phenomena in a few charge-density wave (CDW) materials (CeTe3, ErTe3 and 1T-TaS2) and iron chalcogenide systems (FeTe, FeSe0.44Te0.56 and FeSe). We explore the metastable hidden phases and observe universal dynamics in these materials far from equilibrium.CeTe3 exhibits uni-directional stripe CDW order in thermal equilibrium. Bi-directional CDW is thermodynamically forbidden. After femtosecond laser pulse excitation, the system is driven to a bi-directional order as it crosses a nonthermal fixed point. The new state is formed through associated symmetry changes that cause softening/hardening of CDW-related phonons. The CDW wavevector change proves that Fermi surface nesting (FSN)-enhanced electron-phonon coupling plays a central role in driving the CDW instabilities. Based on these results, we propose a nonthermal phase transition pathway in the non-equilibrium phase diagram.The work in ErTe3 is one step further based on the CeTe3 results. ErTe3 is on the opposite side of the rare-earth tritelluride (RETe3) series to host two orthogonal CDW orders at low temperature. Together with CeTe3 data, the ultrafast results at various temperatures in ErTe3 indicate that the system becomes more symmetric after laser excitation. Given the robustness of the data, the conclusion here may be extended to similar systems as well.The generic features of CDW dynamics in 1T-TaS2 are very similar to those in the quench dynamics of isolated quantum systems (e.g. cold atoms). After laser excitation, the system goes to the prethermalization plateau region before the thermalization stage. We find that both regimes follow universal scalings due to the existence of two nonthermal fixed points. Microscopically, we propose a chiral-symmetry-breaking mechanism that mediates the phase transformation. With a 2500 nm excitation laser, we emphasize the photo-doping, instead of the photo-thermal effect, in driving the phase transition. Due to the lack of thermal energy, the phase transition induced by the 2500 nm laser is more first order-like with faster switching speeds than 800 nm excitation. This high-speed switching with little thermal energy deposition holds promise for better future optoelectronic applications.In FeTe, we directly observed the ultrafast structural transition by ultrafast electron diffraction (UED) for the first time. In the studies of optimally-doped compound FeSe0.44Te0.56, we observed the large-amplitude acoustic phonon excitations at right above the transition temperature Tc. While experiments with better spatial-temporal resolutions are needed, the acoustic phonon observed here might be important for SC in iron chalcogenide. In FeSe, we observed the laser-enhanced local stress that is known to be coupled to the nematic phase and superconductivity. Future UED experiments targeted for understanding the local stress would be very helpful.