Phase Transition in a One-Dimensional Extended Peierls-Hubbard Model with a Pulse of Oscillating Electric Field: III. Interference Caused by a Double Pulse

TL;DR

This study investigates how double pulses of oscillating electric fields influence phase transitions in a one-dimensional extended Peierls-Hubbard model, revealing interference effects that depend on pulse timing and strength, and differ between ionic and neutral phases.

Contribution

It introduces a double pulse approach to analyze interference effects in phase transitions, highlighting the role of coherence in charge density and lattice dynamics.

Findings

Constructive interference occurs at multiples of the lattice vibration period.

Weak pulses show minimal interference due to incoherent lattice oscillations.

Interference strength distinguishes ionic from neutral phase transitions.

Abstract

In order to study consequences of the differences between the ionic-to-neutral and neutral-to-ionic transitions in the one-dimensional extended Peierls-Hubbard model with alternating potentials for the TTF-CA complex, we introduce a double pulse of oscillating electric field in the time-dependent Schr\"odinger equation and vary the interval between the two pulses as well as their strengths. When the dimerized ionic phase is photoexcited, the interference effect is clearly observed owing to the coherence of charge density and lattice displacements. Namely, the two pulses constructively interfere with each other if the interval is a multiple of the period of the optical lattice vibration, while they destructively interfere if the interval is a half-odd integer times the period, in the processes toward the neutral phase. The interference is strong especially when the pulse is strong and short because the coherence is also strong. Meanwhile, when the neutral phase is photoexcited, the interference effect is almost invisible or weakly observed when the pulse is weak. The photoinduced lattice oscillations are incoherent due to random phases. The strength of the interference caused by a double pulse is a key quantity to distinguish the two transitions and to evaluate the coherence of charge density and lattice displacements.