Metallic behaviour of carrier-polarized C$_{60}$ molecular layers: Experiment and Theory

TL;DR

This study demonstrates that injected charge significantly reduces the energy gap of C$_{60}$ molecular layers, leading to metallic behavior, supported by experimental conductance measurements and theoretical calculations.

Contribution

It provides new insights into charge-induced gap reduction in C$_{60}$, combining experimental conductance data with first-principles and Hubbard model calculations.

Findings

C$_{60}$ exhibits metallic conductance when charged.

Injected charge reduces the energy gap of C$_{60}$.

Theoretical models confirm the experimental observations.

Abstract

Although C$_{60}$ is a molecular crystal with a bandgap E$_g$ of ~2.5 eV, we show that E$_g$ is strongly affected by injected charge. In sharp contrast to the Coulomb blockade typical of quantum dots, E$_g$ is {\it reduced} by the Coulomb effects. The conductance of a thin C$_{60}$ layer sandwiched between metal (Al, Ag, Au, Mg and Pt) contacts is investigated. Excellent Ohmic conductance is observed for Al electrodes protected with ultra-thin LiF layers. First-principles calculations, Hubbard models etc., show that the energy gap of C$_{60}$ is dramatically reduced when electrons hop from C$_{60}^-$ to C$_{60}$.