Photoexcitation-Energy-Dependent Transition Pathways from a Dimer Mott Insulator to a Metal

TL;DR

This study uses numerical simulations to explore how different photon energies influence the transition from a Mott insulator to a metal in a two-dimensional organic material, revealing two distinct pathways based on the excitation energy.

Contribution

It demonstrates the photon-energy-dependent pathways of the photoinduced transition, clarifying the roles of effective interaction weakening and carrier introduction in this process.

Findings

Photoexcitation pathways depend on pump photon energy.

Carrier introduction is sensitive to photon energy and occurs rapidly.

Effective interaction weakening occurs slowly regardless of photon energy.

Abstract

We theoretically study pump-photon-energy-dependent pathways of a photoinduced dimer-Mott-insulator-to-metal transition, on the basis of numerical solutions to the time-dependent Schr\"odinger equation for the exact many-body wave function of a two-dimensional three-quarter-filled extended Peierls-Hubbard model. When molecular degrees of freedom inside a dimer are utilized, photoexcitation can weaken the effective interaction or increase the density of photocarriers. In the organic dimer Mott insulator, $ \kappa $-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, the intradimer and the interdimer charge-transfer excitations have broad bands that overlap with each other. Even in this disadvantageous situation, the photoinduced conductivity change depends largely on the pump photon energy, confirming the two pathways recently observed experimentally. The characteristic of each pathway is clarified by calculating the modulation of the effective interaction and the number of carriers involved in low-energy optical excitations. The pump-photon-energy-dependent pathways are confirmed to be realized from the finding that, although the effective interaction is always and slowly weakened, the introduction of carriers is sensitive to the pump-photon energy and proceeds much faster.