Diabatic theory of the dynamical structural change triggered by injection of photoexcited states

Abstract

We study the coherent dynamics of the initial processes of structural change in strongly interacting electronphonon systems triggered by photoexcitation. We employ a model of localized electrons coupled with a single phonon mode, which is fully quantized in order to calculate the dynamics of consecutive switching of potential surfaces. We found that the interplay of the interaction between vibrational degrees of freedom and the Coulomb interaction between electrons is the key to understand the domain growth particularly in higher dimensional systems, which means that the symmetrical properties of the molecular orbitals are reflected in the pattern formation dynamics of the domain growth observed in photoinduced phase transition. We also found that the interference between growing domains affects on there dynamical properties and hence can be detected by accurate measurement.1 Introduction Amongst various phenomena induced by irradiation of light to solids, photoinduced cooperative phenomena have been attracted particular attention of many authors [1][2][3][4]. Above all, one of the main issues with these phenomena is the theory of the dynamics of the initial processes upon photoexcitation, which determines the destiny of the photoexcited state. Since, in particular, those processes take place under nonequilibrium conditions and the coherence of electronic/vibrational states plays an important role, the theory of the quantum-mechanical dynamics of excited states is necessary to understand the initial processes of photoinduced phase transitions.Previous theoretical studies with this respect [5,6] pointed out that the step-by-step conversion of electronic states in a unit cell (molecule) is one of the elementary processes of the phenomena. When the phase transition is accompanied by structural change, we should take into account the effect of strong electronphonon interactions, and the dynamics of excited electrons on potential energy surfaces is important. To be more precise, these processes involve the dynamics of the system with crossing (diabatic) potential surfaces, and thus nonadiabaticity in the dynamics is the key concept in considering a theory in molecular scale.Dynamics of nonadiabatic transitions has been studied since the pioneering works by Landau [7] and Zener [8], and the bifurcation rate of wavefunction was analytically obtained in general cases [9]. These studies mainly focused on the wavefunctions before/after nonadiabatic transition, and hence the time evolution of wavefunctions in coherent regime is out of their scope. On the other hand, the dynamics of nonadiabatic processes has been considered to be important in, for example, photochemical reactions [10]. and hence computational methods of the dynamics have been proposed by many authors [11]. Since, however, those methods require the atomic coordinates/momenta to be classical variables due to the limited computational capacity at the present time, they could discuss the wavefunctions after decoherence of the

Nonlinearity in the Dynamics of Photoinduced Nucleation Process

“…They have mentioned that the dynamics of photoinduced domain growth is a key to understand the physics of the photoinduced cooperativity, and many experimental and theoretical studies have been performed to reveal the mechanism of these phenomena [2,3,5,6,7,4,8,9,10,11]. Above all, interdomain interaction and/or nonlinearity in the pattern formation process of photoinduced domains is important to understand their dynamical properties.…”

“…As for the theoretical study of these phenomena, we have proposed a model of molecular crystals to describe the initial nucleation processes of photoinduced domains [10,11]. We found that an initially excited molecule becomes a nucleus of a photoinduced domain, and that its growth dynamics is understood by the numerical solutions of the time-dependent Schrödinger equation.…”

Coherent dynamics of photoinduced nucleation processes

“…We have pointed out that the population of the excited electronic state | ↑ r is suitable for understanding the dynamics of the initial nucleation processes [10,11]. Thus, we show in Fig.…”

“…As we have shown in the previous papers [10,11], nonadiabaticity of electronic transitions is a key to understand the temporal behavior of the above-mentioned phenomena. Dynamics of nonadiabatic transitions has been studied since the pioneering works by Landau [12] and Zener [13], and the bifurcation rate of wavefunction was analytically obtained in general cases [14].…”

“…As we discussed in our previous papers [10,11], nonadiabatic transitions between quantized states are particularly important to study the dynamical aspects of photoinduced cooperative phenomena.…”