Topologically protected excitons in porphyrin thin films

TL;DR

This paper proposes a novel system of topologically protected exciton edge states in porphyrin thin films, which could lead to robust exciton transport in organic materials for light-harvesting applications.

Contribution

It introduces a new design for topological exciton states in molecular arrays, breaking time-reversal symmetry with a magnetic field to achieve robust transport.

Findings

Topological Frenkel exciton edge states can be realized in porphyrin arrays.

Chiral excitons exhibit robustness against disorder due to topological protection.

The system mimics electronic topological phases using molecular excitons.

Abstract

The control of exciton transport in organic materials is of fundamental importance for the development of efficient light-harvesting systems. This transport is easily deteriorated by traps in the disordered energy landscape. Here, we propose and analyze a system that supports topological Frenkel exciton edge states. Backscattering of these chiral Frenkel excitons is prohibited by symmetry, ensuring that the transport properties of such a system are robust against disorder. To implement our idea, we propose a two-dimensional periodic array of tilted porphyrins interacting with a homogenous magnetic field. This field serves to break time-reversal symmetry and results in lattice fluxes that that mimic the Aharonov-Bohm phase acquired by electrons. Our proposal is the first blueprint for realizing topological phases of matter in molecular aggregates and suggests a paradigm for engineering novel excitonic materials.