Quantum Transport in Molecular Rings and Chains

TL;DR

This paper investigates how deformations in molecular rings and chains influence charge transport, highlighting the role of level crossings, the Longuet-Higgins phase, and topological effects like homeopathic behavior and integral transport.

Contribution

It introduces the concept of homeopathic charge transport in molecular rings and links topological cycles to charge transfer in molecular chains, advancing understanding of deformation-driven transport phenomena.

Findings

Diverging charge transport occurs at gap closures in molecular rings.

Integral charge transport in chains is deformation-independent.

The Jahn-Teller cycle reveals information about hopping amplitude derivatives.

Abstract

We study charge transport driven by deformations in molecular rings and chains. Level crossings and the associated Longuet-Higgins phase play a central role in this theory. In molecular rings a vanishing cycle of shears pinching a gap closure leads, generically, to diverging charge transport around the ring. We call such behavior homeopathic. In an infinite chain such a cycle leads to integral charge transport which is independent of the strength of deformation. In the Jahn-Teller model of a planar molecular ring there is a distinguished cycle in the space of uniform shears which keeps the molecule in its manifold of ground states and pinches level crossing. The charge transport in this cycle gives information on the derivative of the hopping amplitudes.