Author: Christoph Trabant
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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In processing and data storage mainly ferromagnetic (FM) materials are being used. Approaching physical limits, new concepts have to be found for faster, smaller switches, for higher data densities and more energy efficiency. Some of the discussed new concepts involve the material classes of correlated oxides and materials with antiferromagnetic coupling. Their applicability depends critically on their switching behavior, i.e., how fast and how energy efficient material properties can be manipulated. This thesis presents investigations of ultrafast non-equilibrium phase transitions on such new materials. In transition metal oxides (TMOs) the coupling of different degrees of freedom and resulting low energy excitation spectrum often result in spectacular changes of macroscopic properties (colossal magneto resistance, superconductivity, metal-to-insulator transitions) often accompanied by nanoscale order of spins, charges, orbital occupation and by lattice distortions, which make these material attractive. Magnetite served as a prototype for functional TMOs showing a metal-to-insulator-transition (MIT) at T = 123 K. By probing the charge and orbital order as well as the structure after an optical excitation we found that the electronic order and the structural distortion, characteristics of the insulating phase in thermal equilibrium, are destroyed within the experimental resolution of 300 fs. The MIT itself occurs on a 1.5 ps timescale. It shows that MITs in functional materials are several thousand times faster than switching processes in semiconductors. Recently ferrimagnetic and antiferromagnetic (AFM) materials have become interesting. It was shown in ferrimagnetic GdFeCo, that the transfer of angular momentum between two opposed FM subsystems with different time constants leads to a switching of the magnetization after laser pulse excitation. In addition it was theoretically predicted that demagnetization dynamics in AFM should occur faster than in FM materials as no net angular momentum has to be transferred out of the spin system. We investigated two different AFM materials in order to learn more about their ultrafast dynamics. In Ho, a metallic AFM below T ≈ 130 K, we found that the AFM Ho can not only be faster but also ten times more energy efficiently destroyed as order in FM comparable metals. In EuTe, an AFM semiconductor below T ≈ 10 K, we compared the loss of magnetization and laser-induced structural distortion in one and the same experiment. Our experiment shows that they are effectively disentangled. An exception is an ultrafast release of lattice dynamics, which we assign to the release of magnetostriction. The results presented here were obtained with time-resolved resonant soft x-ray diffraction at the Femtoslicing source of the Helmholtz-Zentrum Berlin and at the free-electron laser in Stanford (LCLS). In addition the development and setup of a new UHV-diffractometer for these experiments will be reported
Author: Keiichiro Nasu
Publisher: World Scientific
ISBN: 9814483192
Category : Science
Languages : en
Pages : 354
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Book Description
A new class of insulating solids was recently discovered. When irradiated by a few visible photons, these solids give rise to a macroscopic excited domain that has new structural and electronic orders quite different from the starting ground state. This occurrence is called “photoinduced phase transition”, and this multi-authored book reviews recent theoretical and experimental studies of this new phenomenon.Why and how do photoexcited few electrons finally result in an excited domain with a macroscopic size? How is the resultant photoinduced phase different from the ordinary thermal-induced phase? This review volume answers those essential questions.This book has been selected for coverage in:• CC / Physical, Chemical & Earth Sciences• Index to Scientific Book Contents® (ISBC)
Author: Alfred Zong
Publisher: Springer Nature
ISBN: 3030817512
Category : Science
Languages : en
Pages : 234
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This book advances understanding of light-induced phase transitions and nonequilibrium orders that occur in a broken-symmetry system. Upon excitation with an intense laser pulse, materials can undergo a nonthermal transition through pathways different from those in equilibrium. The mechanism underlying these photoinduced phase transitions has long been researched, but many details in this ultrafast, non-adiabatic regime still remain to be clarified. The work in this book reveals new insights into this phenomena via investigation of photoinduced melting and recovery of charge density waves (CDWs). Using several time-resolved diffraction and spectroscopic techniques, the author shows that the light-induced melting of a CDW is characterized by dynamical slowing-down, while the restoration of the symmetry-breaking order features two distinct timescales: A fast recovery of the CDW amplitude is followed by a slower re-establishment of phase coherence, the latter of which is dictated by the presence of topological defects in the CDW. Furthermore, after the suppression of the original CDW by photoexcitation, a different, competing CDW transiently emerges, illustrating how a hidden order in equilibrium can be unleashed by a laser pulse. These insights into CDW systems may be carried over to other broken-symmetry states, such as superconductivity and magnetic ordering, bringing us one step closer towards manipulating phases of matter using a laser pulse.
Author: Ola Synnergren
Publisher:
ISBN:
Category : Phase transformations (Statistical physics)
Languages : en
Pages : 146
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Author: J. R Helliwell
Publisher: Oxford University Press
ISBN: 9780198500322
Category : Science
Languages : en
Pages : 446
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Book Description
Recent technological advances in synchrotron and neutron sources, detectors, and computer hardware and software have made possible diffraction techniques which collect data at successive moments in time. This is the first book to bring together reviews and research articles covering the three branches of time-resolved diffraction--X-ray, electron, and neutron field. Time-Resolved Diffraction covers gases, liquids, amorphous solids, fibers, and crystals and does so in a multidisciplinary framework which includes examples from molecular biology and chemistry, as well as techniques from physics and materials science. The various time scales of data collection cover ten orders of magnitude, from the sub-pico domain to the kilosecond. Research scientists and graduate students will find this book the most complete compendium of work in this developing field.
Author: Yuan Chen (Researcher on material dynamics)
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Time-resolved spectroscopies of materials provide a wealth of information on material dynamics, and have been a focus of study for decades. With increasing energy and time resolution, time-resolved spectroscopies have been able to detect quasiparticle dynamics, details of electron transport, and ultrafast phase transitions. More recently, as a novel technique, time-resolved resonant inelastic x-ray scattering (trRIXS) is developed and used to investigate spin and charge orders in strongly correlated materials. In this dissertation, I will review the theories of equilibrium and nonequilibrium spectroscopies, with an emphasis on the development of trRIXS theory. Numerical simulation of trRIXS is performed on a single-band tight binding model under the high frequency limit and low frequency limit, revealing Floquet physics and real-time charge oscillation respectively. I will also give examples of applications of time-resolved spectroscopies, especially trRIXS: detecting photoinduced chiral edge states in a graphene nanoribbon and investigating charge excitations in a pumped Mott insulator. Specifically, for the graphene nanoribbon, trRIXS has the potential to selectively probe certain edge states at given energies, providing a conclusive answer to the existence of photoinduced chiral edge states. Finally I will discuss some technical aspects in my implementation of trRIXS code for noninteracting systems. I hope this dissertation can deepen the understanding of pump-probe spectroscopies, especially the novel trRIXS, and provide resources to help design future experiments.
Author: Aaron Michael Lindenberg
Publisher:
ISBN:
Category :
Languages : en
Pages : 280
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Peilin Chen
Publisher:
ISBN:
Category : Laser pulses, Ultrashort
Languages : en
Pages : 274
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Author: Wei Lu
Publisher:
ISBN:
Category :
Languages : en
Pages : 157
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