Photoinduced phase transitions

354 Pages·2004·6.459 MB·English

by  K. Nasu

PHOTO NDUCED
PHASE TRANSITIONS
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PHOTO NDUCED
PHASE TRANSITIONS
editor
k. NASU
High Energy Accelerator Research Organization (KEK),
Japan
WeWorld Scientific
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PHOTOINDUCED PHASE TRANSITIONS
Copyright © 2004 by World Scientific Publishing Co. Pte. Ltd.
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Chee-Hok - Photoinduced Phase.pmd 1 10/4/2005, 6:13 PM
July22,2004 15:12 WSPC/SPI-B204:PhotoinducedPhaseTransitions fm
Preface
There are large varieties of materials around us. In these materials a few
kinds of macroscopic numbers of atoms or molecules are condensed with
a definite composition ratio. Without changing this chemical composition,
a material can undergo various phases from gaseous and liquid phases to
crystalline ones, as temperature decreases from high to low. Even at low
temperatures,amaterialcanundergovariouscrystallinephases,whoselat-
tice structure and electronic state change as temperature decreases. How-
ever, all these states are so-called equilibrium phases, in the sense that the
free energy of each state takes its global minimum at each temperature.
Let us now proceed to the nonequilibrium phases generated from an
equilibriumonebysomeexternalexcitationsorstimulations.Usually,these
states are transient ones having higher energies than the equilibrium one,
but, depending on the way of stimulations or excitations, we can get much
more varieties of states, even if the starting equilibrium phase is the same.
Surelytheyalsorelaxdowntothestartingequilibriumphaseafteraperiod
oftime.However,iftheyarelocallystablestate,inthesensethattheirfree
energy takes local minima separated from the global one by substantial
energy barriers, the time required for the relaxation will be long. In that
case, we can complete necessary observations to determine their charac-
teristics within this period of time. Hence, such a long-lived locally stable
nonequilibrium phase is effectively the same as the equilibrium one.
Very recently a new class of insulating solids was discovered. When
shone by only a few visible photons, the solids give rise to a macroscopic
excited domain that has new structural, electronic and even magnetic
orders quite different from the starting ground state. This phenomenon is
called“photoinducedphasetransition”andwecangeneratenewlong-lived
locallystablemacroscopicnonequilibriumphasesthroughtheexcitationsor
stimulations by a few visible photons. The purpose of this multi-authored
book is to review recent theoretical and experimental studies on this new
phenomenon.
v
July22,2004 15:12 WSPC/SPI-B204:PhotoinducedPhaseTransitions fm
vi Preface
Thephotoinducedphasetransitionstudyhasfirstlystartedbyusingan
organic charge transfer crystal, TTF-CA. At present, however, this study
has extended to many kinds of materials, not only to other organic charge
transfer crystals, but also to various metal complex crystals, Prussian blue
analogues, and even to perovskite type metal oxides.
The standard technique to observe the photoinduced phase transitions
istheso-calledmodulationspectroscopy,inwhichanothervisiblephotonis
shone to detect a spectroscopic change between before and after the tran-
sition. Very recently, however, wesucceeded in observing thephotoinduced
structural phase transition more directly, by using the time-resolved x-ray
diffraction.
One of the most essential points of this research is to clarify “why and
howphotoexcitedfewelectronscanfinallyresultinanexciteddomainwitha
macroscopic size”, worthy to be called a phase transition. Another impor-
tant problem is “how the resultant photoinduced nonequilibrium phase is
differentfromtheordinarythermalinducedphases”.Throughoutthisbook,
we will be fully concerned with these essential problems.
The history of the photoinduced phase transition research is quite
young.Ithasjuststartedandwestillhavevariousunsolvedproblems.There
may be some cases, wherein the same experimental result is understood a
littledifferentway,dependingoneachresearcher.Forthemechanismofthe
photoinducedphasetransitioninTTF-CA,forexample,auniversalunder-
standing that is commonly accepted by all relevant researchers is still not
well established. In this book, we will introduce to readers this immature
situation, just as it is. We believe, however, that such an up-to-date review
willgreatlycontributetothedevelopmentofphotoinducedphasetransition
research.
Keiichiro Nasu
Tsukuba, Japan
October 10, 2003
July22,2004 15:12 WSPC/SPI-B204:PhotoinducedPhaseTransitions fm
Contents
Chapter 1 Theories for Photoinduced Structural Phase
Transitions and their Dynamics 1
Keiichiro Nasu
Chapter 2 Time-Resolved Spectroscopy of the Dynamics of
Photoinduced Ionic-to-Neutral Phase Transition in
Tetrathiafulvalen-P-Chloranil Crystals 71
Katsumi Tanimura
Chapter 3 Study on the Cooperative Photoinduced Low-Spin to
High-Spin State Conversion Processes 117
Osamu Sakai and Tetsuo Ogawa
Chapter 4 Femtosecond Dynamics of the Photo-Induced Lattice
Rearrangements in Quasi-One-Dimensional
Halogen-Bridged Platinum Complexes 161
Tohru Suemoto, Shinichi Tomimoto
and Taira Matsuoka
Chapter 5 Monte Carlo Simulations on Ising-Like Models for
Photoinduced Phase Transitions 197
Tohru Kawamoto and Shuji Abe
Chapter 6 Photoinduced Phase Transitions in One-Dimensional
Correlated Electron Systems 239
Hiroshi Okamoto, Shin-ichiro Iwai
and Hiroyuki Matsuzaki
Chapter 7 Probing Photoinduced Structural Phase Transitions by
Fast or Ultra-Fast Time-Resolved X-Ray Diffraction 309
Herv´e Cailleau, Eric Collet, Marylise Buron-Le Cointe,
Marie-H´el`ene Lem´ee-Cailleau and Shin-ya Koshihara
Index 343
vii
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July7,2004 14:1 WSPC/SPI-B204:PhotoinducedPhaseTransitions chap01
CHAPTER 1
THEORIES FOR PHOTOINDUCED STRUCTURAL
PHASE TRANSITIONS AND THEIR DYNAMICS
Keiichiro Nasu
Solid State Theory Division
Institute of Materials Structure Science, KEK
Graduate University for Advanced Study, 1-1, Oho, Tsukuba
Ibaraki, T305-0801, Japan
E-mail: [email protected]
We review the present status of theoretical studies for photoinduced
structural phase transitions and their dynamics, in connection with the
two key concepts; the hidden multi-stability of the ground state and
the proliferations of optically excited states. Taking the ionic (I) →
neutral (N)phasetransitionintheorganicchargetransfer(CT)crystal,
TTF-CA, as a typical example for this type transition, at first, we the-
oretically show an adiabatic path which starts from CT excitons in the
I-phase, but finally reaches to a N-domain with a macroscopic size. In
connection with this I-N transition, the concept of the initial condition
sensitivityisalsodevelopedsoastoclarifyexperimentallyobservednon-
linear characteristics of this material.
Next, using a more simplified model for the many-exciton system,
we study theoretically the early time quantum dynamics of the exciton
proliferation, which finally results in the formation of a domain with a
largenumberofexcitons.Forthispurpose,wederiveastepwiseiterative
equation to describe the exciton proliferation and clarify the origin of
the initial condition sensitivity.
Possible differences between a photoinduced nonequilibrium phase
and an equilibrium phase at high temperatures are also clarified from
generalandconceptionalpointsofview,inconnectionwithrecentexper-
imentsonthephotoinducedphasetransitioninanorgano-metalliccom-
plex crystal. It will be shown that the photoinduced phase can make
a new interaction appear as a broken symmetry only, even when this
interaction is almost completely hidden in all the equilibrium phases,
such as the ground state and other high-temperature phases. The rela-
tionbetweenthephotoinducednonequilibriumphaseandthehysteresis
induced nonequilibrium one is also qualitatively discussed.
1