Delocalization of tightly bound excitons in disordered systems

TL;DR

This paper investigates how electron-electron interactions influence the localization length of excitons in disordered systems, revealing a significant enhancement near the Fermi energy, with implications for understanding electronic conductance.

Contribution

It provides the first detailed calculation of exciton localization length in disordered systems, highlighting the differential effects of interactions on charge and thermal conductance.

Findings

Electron-electron interactions strongly enhance exciton localization length.

Localization length related to thermal conductance is more affected than charge conductance.

Delocalization mechanism is more efficient near the Fermi energy for electron-hole pairs.

Abstract

The localization length of a low energy tightly bound electron-hole pair (excitons) is calculated by exact diagonalization for small interacting disordered systems. The exciton localization length (which corresponds to the thermal electronic conductance) is strongly enhanced by electron-electron interactions, while the localization length (pertaining to the charge conductance) is only slightly enhanced. This shows that the two particle delocalization mechanism widely discussed for the electron pair case is more efficient close to the Fermi energy for an electron-hole pair. The relevance to experiment is also discussed.