Phase coherence in tight-binding models with nonrandom long-range hopping

TL;DR

This paper investigates how long-range hopping in tight-binding models affects phase coherence and density of states, revealing conditions for infinite coherence length even with disorder, with implications for exciton transport.

Contribution

It introduces a theoretical analysis of phase coherence in disordered tight-binding models with long-range hopping, highlighting conditions for infinite coherence length at the band tail.

Findings

Infinite phase coherence length for outermost tail states within certain hopping ranges

Long-range hopping causes tail states to exhibit ballistic transport despite disorder

Implications for optical response and energy transport in molecular aggregates

Abstract

The density of states, even for a perfectly ordered tight-binding model, can exhibit a tail-like feature at the top of the band, provided the hopping integral falls off in space slowly enough. We apply the coherent potential approximation to study the eigenstates of a tight-binding Hamiltonian with uncorrelated diagonal disorder and long-range hopping, falling off as a power $\mu$ of the intersite distance. For a certain interval of hopping range exponent $\mu$, we show that the phase coherence length is infinite for the outermost state of the tail, irrespectively of the strength of disorder. Such anomalous feature can be explained by the smallness of the phase-space volume for the disorder scattering from this state. As an application of the theory, we mention that ballistic regime can be realized for Frenkel excitons in two-dimensional molecular aggregates, affecting to a large extent the optical response and energy transport.