Successive Structural Changes and Their Dynamics in Multi-Stepwised Potential-Crossing Systems via Multi-Photoexcitations

We investigate the dynamical nature in multi-stepwised potential-crossing systems which are proposed as an elementary process of the structural phase transition in the strongly coupled electron-phonon systems, in order to clarify the effects of multi-photoexcitations and lattice relaxations on the successive structural changes in this system. We calculate the time-developments of the density operator of this system both for the diabatic and adiabatic cases using an unified model Hamiltonian. It is concluded from calculated results that in the both cases the system develops from the lowest-energy potential state to the higher ones by the effects of the multi-photoexcitation together with the lattice relaxation. In the diabatic case, the photoexcitation is essential for the successive structural changes, because the structural change is not expected only by the weak electronic interaction between potentials. In the adiabatic case, on the other hand, the system changes from the lowest to the higher potential states going up through the adiabatic potential surface of the ground state with the help of the multi-photoexcitations.