Electroluminescence rectification and high harmonic generation in molecular junctions

TL;DR

This paper models molecular junctions using advanced nonequilibrium Green's functions to explore electroluminescence and high harmonic generation, revealing effects similar to solid-state systems.

Contribution

It introduces a time-linear formalism to simulate molecular electronics on experimentally relevant timescales, capturing electroluminescence and harmonic generation phenomena.

Findings

Pronounced electroluminescence observed in molecular junctions.

High harmonic generation with symmetry-dependent suppression or enhancement.

Mechanisms resemble solid-state effects more than isolated molecules.

Abstract

The field of molecular electronics has emerged from efforts to understand electron propagation through single molecules and to use them in electronic circuits. Serving as a testbed for advanced theoretical methods, it reveals a significant discrepancy between the operational time scales of experiments (static to GHz frequencies) and theoretical models (femtoseconds). Utilizing a recently developed time-linear nonequilibrium Green's functions formalism, we model molecular junctions on experimentally accessible timescales. Our study focuses on the quantum pump effect in a Benzenedithiol molecule connected to two copper electrodes and coupled with cavity photons. By calculating both electric and photonic current responses to an ac bias voltage, we observe pronounced electroluminescence and high harmonic generation in this setup. The mechanism of the latter effect is more analogous to that from solids than from isolated molecules, with even harmonics being suppressed or enhanced depending on the symmetry of the driving field.