50 research outputs found
Real Time Quantum Dynamics of Spontaneous Translational Symmetry Breakage in the Early Stage of Photo-induced Structural Phase Transitions
Real time quantum dynamics of the spontaneous translational symmetry breakage
in the early stage of photoinduced structural phase transitions is reviewed and
supplementally explained, under the guide of the Toyozawa theory, which is
exactly in compliance with the conservation laws of the total momentum and
energy. At the Franck Condon state, an electronic excitation just created by a
visible light, is in a plane wave state, extended all over the crystal. While,
after the lattice relaxation having been completed, it is localized around a
certain lattice site of the crystal, as a new excitation. Is there a sudden
shrinkage of the excitation wave function, in between. The wave function never
shrinks, but only the spatial, or inter lattice site quantum coherence,
interference of the excitation disappears, as the lattice relaxation proceeds.
This is nothing but the spontaneous breakage of translational symmetry.Comment: Applied Science 2018, MDP
Cooperative domain type interlayer -bond formation in graphite
Using the classical molecular dynamics and the semiempirical Brenner's
potential, we theoretically study the interlayer sigma bond formation, as
cooperative and nonlinear phenomena induced by visible light excitations of a
graphite crystal. We have found several cases, wherein the excitations of
certain lattice sites result in new interlayer bonds even at non-excited sites.
We have also found that, a new interlayer bond is easier to be formed around a
bond, if it is already existing. As many more sites are going to be excited,
the number of interlayer bonds increases nonlinearly with the number of excited
sites. This nonlinearity shows 1.7 power of the total number of excited sites,
corresponding to about three- or four-photon process.Comment: 7 pages, 8 figure
Probing Ultrafast Dynamics of Polarization Clusters in BaTiO₃ by Pulsed Soft X-Ray Laser Speckle Technique
Coherent dynamics of photoinduced nucleation processes
We study the dynamics of initial nucleation processes of photoinduced
structural change of molecular crystals. In order to describe the nonadiabatic
transition in each molecule, we employ a model of localized electrons coupled
with a fully quantized phonon mode, and the time-dependent Schr\"odinger
equation for the model is numerically solved. We found a minimal model to
describe the nucleation induced by injection of an excited state of a single
molecule in which multiple types of intermolecular interactions are required.
In this model coherently driven molecular distortion plays an important role in
the successive conversion of electronic states which leads to photoinduced
cooperative phenomena.Comment: 14 pages, 5 figure