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K. Ishida
When, for example, ultrashort laser pulses are used as a probe, transient electronic
properties are detected through the slight change of optical properties, which helps
us understand the physics in ultrafast timescale.
Another example of the interesting transient phenomena is the structural dynamics. Time-resolved x-ray or electron diffraction measurement has been intensively
developed, and the dynamics of photoinduced structural change or chemical reaction
is currently being discussed by many authors [7, 8]. Furthermore, as various experimental methods have been developed to understand transient phenomena [9, 10],
it is quite important to combine as many experimental data as possible in order to
obtain an overall picture for the transient dynamics of certain materials. We, however,
should point out that we need a unified physical model to understand all the experimental data on a single phenomenon. In particular, when we are interested in time
evolution of excited states, we consider that a first step to construct an appropriate
model is an accurate description of photoexcitation/deexcitation processes.
Considering that electromagnetic field has been regarded as classical external
field in many theoretical studies, we study the quantum dynamics of electronic systems under photoirradiation, focusing on the wavepacket states created by photons.
We consider that we will have a reliable information on the response to various
probes and the entanglement properties between multiple degrees of freedom by
determining the quantum nature of those created wavepackets. Since, however, it
is not straightforward to obtain a first-principles theory for transient dynamics, we
focus on the interplay of electron-phonon interaction and electron-photon (electric
dipole) interaction as a first step to construct a general theory of transient photoexcitation/deexciation phenomena. For this purpose we chose a model of coupled
electron-phonon-photon systems and solved the time-dependent Schrödinger equation for fully quantized systems in order to discuss the wavepacket motion in the
presence of electromagnetic field.
We also mention that nonadiabatic coupling between potential energy surfaces
(PESs) is a key to understand the relaxation dynamics of photoexcited states, e.g.,
photoinduced nucleation [11]. Furthermore, when electrons, phonons, and photons
are considered at the same time, the Raman processes are expected to give significant contribution to the electronic transitions, which means that the photoexcitation/deexcitation process of electron-phonon systems should be carefully dealt with
in order to understand the ultrafast dynamics with light-matter interaction. As well
as the intermodal coherence mediated by the Raman processes [12], we stress that it
is worth while mentioning that previous studies [13–16] have shown that the conical
intersection (CI) in the “classical” adiabatic PESs also is a key to understand the
wavepacket dynamics. These results show us that the coexistence of nonadiabatic
coupling between PESs and Raman scattering processes gives another viewpoint on
the coherent dynamics of electron-phonon-photon systems. The aim of the present
paper is to study the interplay of electron-phonon nonadiabaticity and Raman scattering processes by numerical calculations with a toy model.
K. Ishida
When, for example, ultrashort laser pulses are used as a probe, transient electronic
properties are detected through the slight change of optical properties, which helps
us understand the physics in ultrafast timescale.
Another example of the interesting transient phenomena is the structural dynamics. Time-resolved x-ray or electron diffraction measurement has been intensively
developed, and the dynamics of photoinduced structural change or chemical reaction
is currently being discussed by many authors [7, 8]. Furthermore, as various experimental methods have been developed to understand transient phenomena [9, 10],
it is quite important to combine as many experimental data as possible in order to
obtain an overall picture for the transient dynamics of certain materials. We, however,
should point out that we need a unified physical model to understand all the experimental data on a single phenomenon. In particular, when we are interested in time
evolution of excited states, we consider that a first step to construct an appropriate
model is an accurate description of photoexcitation/deexcitation processes.
Considering that electromagnetic field has been regarded as classical external
field in many theoretical studies, we study the quantum dynamics of electronic systems under photoirradiation, focusing on the wavepacket states created by photons.
We consider that we will have a reliable information on the response to various
probes and the entanglement properties between multiple degrees of freedom by
determining the quantum nature of those created wavepackets. Since, however, it
is not straightforward to obtain a first-principles theory for transient dynamics, we
focus on the interplay of electron-phonon interaction and electron-photon (electric
dipole) interaction as a first step to construct a general theory of transient photoexcitation/deexciation phenomena. For this purpose we chose a model of coupled
electron-phonon-photon systems and solved the time-dependent Schrödinger equation for fully quantized systems in order to discuss the wavepacket motion in the
presence of electromagnetic field.
We also mention that nonadiabatic coupling between potential energy surfaces
(PESs) is a key to understand the relaxation dynamics of photoexcited states, e.g.,
photoinduced nucleation [11]. Furthermore, when electrons, phonons, and photons
are considered at the same time, the Raman processes are expected to give significant contribution to the electronic transitions, which means that the photoexcitation/deexcitation process of electron-phonon systems should be carefully dealt with
in order to understand the ultrafast dynamics with light-matter interaction. As well
as the intermodal coherence mediated by the Raman processes [12], we stress that it
is worth while mentioning that previous studies [13–16] have shown that the conical
intersection (CI) in the “classical” adiabatic PESs also is a key to understand the
wavepacket dynamics. These results show us that the coexistence of nonadiabatic
coupling between PESs and Raman scattering processes gives another viewpoint on
the coherent dynamics of electron-phonon-photon systems. The aim of the present
paper is to study the interplay of electron-phonon nonadiabaticity and Raman scattering processes by numerical calculations with a toy model.