2001 Fiscal Year Final Research Report Summary
Dynamics of Photoinduced Phase Transitions in Low-Dimensional Electron-Lattice Systems
| Project/Area Number |
11215201
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| Research Category |
Grant-in-Aid for Scientific Research on Priority Areas (B)
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| Allocation Type | Single-year Grants |
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| Review Section |
Science and Engineering
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| Research Institution | Osaka University Department of Physics (2000-2001)
Tohoku University (1999) |
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Principal Investigator |
OGAWA Tetsuo Osaka University, Department of Physics, Professor, 大学院・理学研究科, 教授 (50211123)
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| Project Period (FY) |
1999 – 2001
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| Keywords | photoinduced phase transitions / electron-lattice systems / spatiotemporal dynamics / domino process / phase separation / finite lifetime / exciton bosonization / 量子常誘電体 |
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| Research Abstract |
(1) THEORY OF PHOTOlNDUCED PHASE TRANSITIONS VIA EXCITED STATES - PHOTOINDUCED DOMINO PROCESS : Photoinduced structural phase transitions via excited electronic states are discussed theoretically using a one-dimensional model composed of localized electrons and lattices under the adiabatic or diabatic approximation. We show that the global structural change by photoexcitation only at a site is possible, and we clarify conditions for the occurrence of such phenomena. Spatiotemporal dynamics of nonequilibrium first-order phase transitions is also investigated in detail in terms of photoinduced nucleation and domino processes of the domain boundaries (domain walls). In the adiabatic regime, after the spontaneous emission of a photon, an initial local structural change (i) remains locally, (ii) induces cooperatively a global structural change, or (iii) disappears and returns to the initial phase, depending on the strength of the interaction between neighboring sites. Dynamical features of
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the case (ii) are characterized by the deterministic domino process ; domain walls between the two phases move deterministically at a constant velocity (with changing speed) without further spontaneous emissions in the case of strong (weak) dissipation. In the diabatic regime, similar three types of structural change exist. The domain-wall dynamics is described as the stochastic domino process, which is accompanied by the successive radiative transitions. A new theoretical treatment is also proposed to study crossover between the adiabatic and diabatic regimes. We also clarify dependence on the friction (energy dissipation rate). We find novel photoinduced domino process in the case of weak friction and strong intersite interaction. In this domino motion the photoexcited site is still in an excited electronic state.
(2) THEORY OF PHASE-SEPARATION DYNAMICS IN FINITE-LIFETIME SYSTEMS : We study theoretically dynamics of the spinodal decomposition in finite-lifetime systems to clarify effects of the interparticle interactions beyond the Ginzburg-Landau-Wilson phenomenology. This is based on the coarse-grained Hamiltonian derived from the interacting lattice-gas model with a finite lifetime. The information of the system is reduced to closed-form coupled integrodifferential equations for the single-point distribution function and the dynamical structure factor. These equations involve explicitly the interparticle interactions. We find quantitatively that the finite lifetime prevents the phase separation and the order formation in the cw creation case. A universal relation between the lifetime and the asymptotic characteristic wavenumber is confirmed numerically.
(3) BOSON THEORY OF MANY-EXCITON SYSTEMS : We derive a bosonized Hamiltonian describing two-exciton correlation of semiconductor-photon coupled systems with a new bosonization method, which takes into full account an effect of deviation of the excitons from ideal bosons. This deviation effect stems from that the excitons are composite particles, whose character appears clearly in the case where the excitons overlap with each other. We call this effect a composite-particle effect (CPE). The Hamiltonian derived in this study includes the results of the previous works as low-order terms of the CPE. After introduction of general theory, of the bosonization method for arbitrary dimension and electron-hole mass ratio, we demonstrate also application to a semiconductor bulk system coupled with a photon field in the heavy-hole limit. The bosonized Hamiltonian shows that the CPE brings about enhancement of exciton-exciton scattering strength and qualitative change of photo-transition amplitude. It is also shown that the Hamiltonian describes two-exciton bound and scattering states.
(4) PHENOMENOLOGICAL THEORY OF PHOTOINDUCED COOPERATIVE PHENOMENA IN QUANTUM PARAELECTRICS : We theoretically study an electron-dipole induced phase transition in photoexcited quantum paraelectrics on the basis of the transverse Ising model taking account of the interaction between a soft-mode phonon-dipole and a photodoped electron-dipole. In accordance with the mean-field approximation, temperature-dependence of dielectric susceptibilities exhibits paraelectric to ferroelectric phase transitions when the concentration of the electron-dipole and the interaction between a phonon-dipole and an electron-dipole take appropriate values. These values separately have lower limits in order to occur phase transitions. We also investigate dependence of dielectric susceptibilities on a uniform electric field. Less
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Research Products
(33 results)
