Polaronic states with Spin-Charge-Coupled Excitation in a 1D Mott Insulator K-TCNQ

TL;DR

This paper investigates the nature of photoinduced midgap states in a 1D Mott insulator, revealing the importance of intermolecular lattice distortions and identifying two distinct types of polaronic states.

Contribution

It introduces a theoretical model incorporating both intermolecular and intramolecular phonons and uses DMRG to analyze the resulting midgap states in K-TCNQ.

Findings

Intermolecular lattice distortion is essential for reproducing midgap absorption.

Identification of two types of midgap states: polaronic and a superposition of doped-carrier and triplet-dimer states.

Superposition states are generally observed in 1D dimerized Mott insulators.

Abstract

We discuss photogenerated midgap states of a one-dimensional (1D) dimerized Mott insulator, potassium-tetracyanoquinodimethane (K-TCNQ). Two types of phonon modes are taken into account: intermolecular and intramolecular vibrations. We treat these phonon modes adiabatically and analyze a theoretical model by using the density-matrix renormalization group (DMRG). Our numerical results demonstrate that the intermolecular lattice distortion is necessary to reproduce the photoinduced midgap absorption in K-TCNQ. We find two types of midgap states. One is a usual polaronic state characterized by a localized elementary excitation. The other is superposition of two types of excitations, a doped-carrier state and a triplet-dimer state, which can be generally observed in 1D dimerized Mott insulators, not limited to K-TCNQ.