[PDF] Nonequilibrium Dynamics Of Charge And Collective Modes In Charge Density Wave Compounds eBook

Author : L.P. Gor'kov
Publisher : Elsevier
Page : 495 pages
File Size : 35,46 MB
Release : 2012-12-02
Category : Science
ISBN : 0444600736

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The latest addition to this series covers a field which is commonly referred to as charge density wave dynamics. The most thoroughly investigated materials are inorganic linear chain compounds with highly anisotropic electronic properties. The volume opens with an examination of their structural properties and the essential features which allow charge density waves to develop. The behaviour of the charge density waves, where interesting phenomena are observed, is treated both from a theoretical and an experimental standpoint. The role of impurities in statics and dynamics is considered and an examination of the possible role of solitons in incommensurate charge density wave systems is given. A number of ways to describe charge density waves theoretically, using computer simulations as well as microscopical models, are presented by a truely international board of authors.

Author :
Publisher :
Page : 109 pages
File Size : 22,26 MB
Release : 2013
Category :
ISBN : 9781303634444

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Below I present two related studies on the dynamics of spin-/charge-density-waves (SDW/CDW) in chromium. In the first study we measured equilibrium fluctuations of antiferromagnetic SDW/CDW domains in a bulk sample by correlating speckle patterns obtained with partially coherent synchrotron x-rays. The autocorrelation functions follow a double compressing exponential decay similar to that observed in other `jammed' condensed matter systems. This hyper-diffusive behavior indicates the existence of collective relaxation modes which we interpret to arise from the coherent rotation of weakly coupled blocks of spins. Time scales for this collective process range from tens of seconds at 150 Kelvin to thousands of seconds at low temperatures. Even near absolute zero, we observed fluctuations of the magnetic structure which can most directly be interpreted as arising from quantum mechanical zero-point motion. Because microscopic domains of energetically similar spin/charge ordered states are quantum mechanically linked, there exists a dynamic competition between alternate ground states that provides insight into the free energy landscape of domain wall configurations. We obtain estimates of the effective soliton mass of a domain wall and the Arrhenius activation energy.

Author : Emre Ergeçen
Publisher :
Page : 50 pages
File Size : 35,4 MB
Release : 2019
Category :
ISBN :

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Charge density wave (CDW) is a periodic charge modulation in a metal, induced by electron-phonon or electron-electron interaction, which breaks the translational symmetry of the underlying electron gas. The charge density wave order is ubiquitous among condensed matter systems, and its equilibrium properties have been well characterized by static probes, such as X-ray scattering. However, little is known about their nonequilibrium properties following photoexcitation. In this thesis, we use time resolved optical measurements to characterize the nonequilibrium dynamics of charge density wave systems. In the time resolved optical experiments in this work, an ultrashort (

Author : Felix Tilman Schmitt
Publisher :
Page : pages
File Size : 32,54 MB
Release : 2011
Category :
ISBN :

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In condensed matter, electrons are not independent but are coupled to their neighbors via interactions; they are said to be correlated. This fact that electronic states are aware of their neighbors' states and changes thereof gives rise to a rich variety of properties and physics that defines the nature around us. Correlations in condensed matter can range in their effect from slight changes in the band structure to the emergence of order and symmetry breaking, which lead to novel properties and phases. These correlations exhibit themselves on different time scales. Mott-insulators, in which strong Coulomb repulsion between electrons splits a half-filled conduction band to result in an insulator, can have a band gap of several eV. On the other hand, transitions into the superconducting or charge density wave state, for example, happen on energy scales within several tens to hundreds of meV of EF. Despite the plethora of phenomena arising from these correlations, this many-body problem is hard to tackle and there is still much to be learned. This work investigates different aspects of correlated systems in and out of equilibrium with angle resolved photoemission (ARPES), and time resolved ARPES, two powerful spectroscopic techniques that are able to elucidate the dynamics and mechanics of correlations. Starting out, the experimental ARPES setup is introduced, and the ARPES system located in the Geballe Laboratory for Advanced Materials at Stanford University is described in more detail, since its maintenance and enhancement were an integral part of this work. In the following, the high energy properties of Nd2-xCexCuO4+d (NCCO) are investigated with ARPES. NCCO belongs to the electron doped side of a class of materials called high temperature superconducting Cuprates (HTSCs), so called because of their unusually high transition temperatures. The HTSCs exhibit a plethora of rich physics; including the anti-ferromagnetic insulating phase of the undoped parent compound dominated by Mott-Hubbard physics to the superconducting dome which features superconductivity with a d-wave symmetry whose origin is still a mystery. The hole doped HTSCs show a vertical band dispersion in ARPES measurements around 0.3 eV which was termed the high energy anomaly (HEA). Here, a systematic study of high energy features on NCCO revealed a similar HEA, albeit around 0.6 eV binding energy. We were able to successfully explain the HEA within the Hubbard model as being a cross-over from the quasi particle band resulting from doping and the lower or upper Hubbard band, depending on doping. The simulations also captured the difference in energy scale between hole and electron doping. Next, focusing on energies within several tens of meV of EF, a different energy scale of NCCO is explored. In the hole doped HTSCs, a discontinuity of the electronic dispersion around 50-70 meV was observed both in the region of the Brillouin zone were the d-wave superconducting gap had a node ("nodal") and where it had a maximum ("antinodal"). Conversely, in the electron doped materials this kink could only be observed in the antinodal region. If the discontinuity or "kink", which is hypothesized to originate from electron phonon coupling to certain Oxygen modes, is related to superconductivity, one would imagine it to have the same universality as the observed superconductivity. Our work demonstrates that new and improved ARPES data show a kink in the nodal region of NCCO as well, giving this discontinuity universality among the HTSCs. Superconductivity (SC) (at least conventional, electron phonon mediated superconductivity according to Bardeen-Cooper-Schrieffer) is closely related to its brethren, the spin- (SDW) or charge-density waves (CDW): all are mediated by different channels of the same type of interaction. The non-equilibrium dynamics and excitation modes of CDWs and SCs are closely related. Time resolved ARPES (tr-ARPES) is able to probe both non-equilibrium dynamics and collective excitation modes in real time. Continuing, this work explores the non-equilibrium physics of TbTe3, a model system for studying charge density waves. Our systematic study of the transient dynamics in dependence of excitation density revealed a complex picture ranging all the way from a weakly perturbed regime, in which collective modes were evident to a strongly perturbed regime, where we could observe the transient melting of the CDW state. This unprecedented insight into the dynamics of interactions will enhance our future understanding of correlated materials. Through the strengths of tr-ARPES, we were able to assign one of the collective modes we observed to the amplitude mode of the CDW. This provides a major stepping stone towards seeing a similar amplitude mode in superconductors. Especially in novel superconductors like the HTSCs or the Pnictides, where the mechanism of superconductivity is still debated, the observation of such collective modes could greatly aid towards their understanding which is needed in order to eventually exploit their huge potential for real-life applications.

Author : Edoardo Baldini
Publisher : Springer
Page : 360 pages
File Size : 25,99 MB
Release : 2018-03-28
Category : Technology & Engineering
ISBN : 3319774980

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This book studies the dynamics of fundamental collective excitations in quantum materials, focusing on the use of state-of-the-art ultrafast broadband optical spectroscopy. Collective behaviour in solids lies at the origin of several cooperative phenomena that can lead to profound transformations, instabilities and phase transitions. Revealing the dynamics of collective excitations is a topic of pivotal importance in contemporary condensed matter physics, as it provides information on the strength and spatial distribution of interactions and correlation. The experimental framework explored in this book relies on setting a material out-of-equilibrium by an ultrashort laser pulse and monitoring the photo-induced changes in its optical properties over a broad spectral region in the visible or deep-ultraviolet. Collective excitations (e.g. plasmons, excitons, phonons...) emerge either in the frequency domain as spectral features across the probed range, or in the time domain as coherent modes triggered by the pump pulse. Mapping the temporal evolution of these collective excitations provides access to the hierarchy of low-energy phenomena occurring in the solid during its path towards thermodynamic equilibrium. This methodology is used to investigate a number of strongly interacting and correlated materials with an increasing degree of internal complexity beyond conventional band theory.

Author : Gyula Hutiray
Publisher : Springer
Page : 564 pages
File Size : 32,62 MB
Release : 1985
Category : Science
ISBN :

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Neutron and x-ray scattering study on K0.3MoO3 and other quasi one dimensional conductors -- X-ray study of charge-density wave in K0.30Mo03 under electric fields -- Transmission electron microscopy for imaging and diffraction studies of low dimensional transition metal chalcogenides -- Aspects of charge-density waves in the TaTe4-NbTe4 structures and in 2H-TaSe2 -- Charge density waves, phasing, sliding and related phenomena in NbSe3 and other transition metal chalcogenides -- Structural and electrical properties interpretation through band structure calculations on the (MSe4)nI SERIES (M = Nb, Ta). -- Defects and charge density waves in irradiated layer and chain compounds -- Electron diffraction charge density wave studies in the chalcogenide compounds (MX4)nI -- Neutron studies of the blue bronzes K0.3MoO3 and Rb0.3MoO3 -- The effect of a magnetic field on the discotm1ensurate to commensurate transition in 2H TaSe2 -- High pressure investigation of the cdw phase diagram of 1T-TaS2 -- Landau theory of 2H-TaSe2 -- Multidomain structures of incommensurate phases in CDW states of 2H-TaSe2 -- Electron microscopy of charge density wave defects in 1T-TaS2 and 1T-TaSe2 -- Aspects of strong electron-phonon coupling related to the CDW transition at temperatures above it -- Elastic and other properties at the commensurate-incommensurate transition in 2H-TaSe2 -- CDW phase mode investigation in the FIR in K0.3MaO3 and band structure calculation -- 93Nb NMR study of CDW in (NbSe4)10/3I single crystal -- Electronic Properties and Fe57 Mössbauer measurements of T1+xNb3-xSe10 with T = Fe, Cr -- Transport and Mössbauer studies of the peierls transition in Fe-doped K0.30MoO3 -- Charge density wave instabilities in quasi two-dimensional oxides n-Mo4O11 and ?-Mo4O11 -- Thermal conductivity of layered dichalcogenides -- Tunneling study of commensurate charge density wave states in 1T-TaS2 -- Galvanomagnetic properties of the quasi-two dimensional purple bronze K0.9Mo6O17 -- Non-local elastic forces in charge-density wave systems -- Soliton model of charge-density-wave depinning -- Dynamics of incommensurate structures -- Some problems arising from electrostatic potential in CDW behavior -- The single domain model of charge-density wave transport -- On the microscopic theory of kinetic phenomena in peierls conductors -- Near commensurability effects on charge density wave dynamics -- Shift in the longitudinal sound velocity due to sliding charge density waves -- Microscopic local mechanisms for "Noises" generated by moving CDW -- Phase vortices and CDW conduction noise -- Damping of CDW-condensate motion by interaction with thermal phasons -- Microscopic theory of interaction of CDW with impurities -- Quantum effects in the Josephson approach to a CDW -- Fokker planck theory of the classical charge density wave model with current noise -- Travelling charge density waves : A mean field treatment -- Coherent and incoherent effects in charge density wave transport -- Threshold field, electrical conductivity and time-dependent voltage in transition metal tri- and tetrachalcogenides -- Solitons in TaS3 experiment -- Thermal gradient experiments on the charge-density-wave conduction noise spectrum -- Broadband noise in orthorhombic TaS3 -- High field I-V characteristics of orthorhombic TaS3 -- Inertial dynamics of CDW transport in NbSe3 -- Frequency dependent conductivity of CDW compounds -- AC conductivity of the blue bronze K0.3 MoO3 -- Subharmonic shapiro steps, devil's staircase, and synchronization in RF-driven CDW conductors -- Mode locking and chaos in sliding charge-density-wave systems -- Chaos in charge density wave systems -- Contribution of CDW motion to the hall effect and to the transverse conductivity in TaS3. experiment -- Contribution of CDW motion to the hall effect and to the transverse conductivity. Theory -- Dependence of the elastic modulus of TaS3 on the CDW current -- Low frequency elastic properties of materials containing a sliding CDW -- The conductivity of orthorhombic TaS3 under uniaxial strain -- Ohmic and nonlinear transport of (TaSe4)2I under pressure -- Pinning, metastability and sliding of charge-density-waves -- Distortion, metastability and breaking in charge-density wave transport: Recent experiments on niobium triselenide, suggesting a new mean-field approach -- Bistable configurations of the pinned charge density wave: Random-field-model dynamics observed in rearrangement prior to depinning -- Electric field induced relaxation of metastable states in TaS3 -- Remanent deformation of CDWs -- Relaxation of the deformed cdw state: electric and thermal hysteresis -- Thermal hysteresis in the thermopower of o-TaS3 -- Delayed switching between normal and CDW conducting states in o-TaS3 -- The effect of uniaxial strain on metastable states in TaS3 -- Influence of defects on the metastable states of o-TaS3 -- Charge density wave transport in the blue bronzes K0.30MoO3 and Rb0.30MoO3 : metastability, hysteresis and memory effects -- Effects of irradiation on the blue bronzes K0.30MoO3 and Rb0.30MoO3 -- Relaxation of metastable states in blue bronze K0.3MoO3 -- Incommensurate ferroelectrics -- Commensurate and incommensurate phases of a two-dimensional lattice of superconducting vortices -- (TMTSF)2X compounds: Superconductivity, spin-density waves and anion ordering -- Impurity pinning in quasi-1D superconductivity -- Numerical studies of the effect of a wall on SDW in a jellium -- Pinning of amplitude solitons in Peierls systems with impurities -- New resistive state in low dimensional superconductor TaSe3 -- Switching in cdw systems and in V02 -- A comparative study -- The effect of varying the bandfilling in a Peierls conductor -- Solitons and polarons in a spin density wave chain -- Charge density waves in superionic conductors -- Numerical study of impurity pinning in one-dimensional interacting electron systems -- Multivalued charge-density waves.

Author : Wen Shen
Publisher :
Page : 348 pages
File Size : 21,37 MB
Release : 2013
Category : Low temperatures
ISBN :

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The fast development of time resolved photoemission (TRPES) techniques allow us to discover the rich features of nonequilibrium phenomena which may not appear in equilibrium. One of the most explored topics is the nonequilibrium behavior of a charge density wave (CDW) material. Being an ordered phase at low temperature, the CDW state provides a fertile ground to study electron-electron and electron-ion interactions. By driving this material out of equilibrium and taking ultrafast time resolution snapshots of its behavior, TRPES helps us understand these interactions and sheds light on the mechanisms behind these and other complex material properties, such as metal-insulator transitions, high temperature superconductivity, and magnetic phenomena. Recent experiments on TRPES in CDW materials show an ultrafast CDW gap closure in systems such as 1T-TaS2 and TbTe3 and the subsequent separation of time scales for the electron-electron interaction and the electron-lattice interaction. But it is still not clear what happens during the ultrashort period (in first 100 femtosecond). In this dissertation, we solve a two band model describing this ultrafast process in a CDW system. By fixing the lattice distortion effect in the CDW, we studied the nonequilibrium excitations of the electrons under a strong electric field. This research is performed by calculating nonequilibrium Green's functions (NGF) along the Kadanoff-Baym-Keldysh contour. We solved this nonequilibrium problem exactly. We show non-perturbative results and explore the nonlinear electronic behavior under an ultrashort light pulses. In addition to the TRPES problem, we also examined the behavior of Bloch oscillations under a large DC field, the response to an AC electric field, high harmonic generation from solids, and the crossover between frequency-driven excitation and amplitude-driven excitation.