Tunneling diodes under environmental effects

TL;DR

This paper investigates the robustness of single-molecule tunneling diodes against environmental effects, showing they remain effective under certain decoherence conditions and proposing design improvements for enhanced rectification.

Contribution

It introduces a phenomenological model of environmental effects on molecular diodes and suggests a refined four-orbital design to improve rectification ratios.

Findings

Rectification ratios reach three orders of magnitude without environmental interactions.

Diodes remain effective with decoherence when γ_d ≲ v, with ratios reduced by a factor of 2-4.

Proposed four-orbital design enhances rectification performance.

Abstract

We examine the robustness of single-molecule tunneling diodes to thermal-environmental effects. The diode comprises three fragments: two different conjugated chemical groups at the boundaries, and a saturated moiety in between, breaking conjugation. In this setup, molecular electronic levels localized on the conjugated groups independently shift with applied bias. While in the forward polarity a resonance condition is met, enhancing conductance, in the reversed direction molecular electronic states shift away from each other, resulting in small tunneling currents. In the absence of interactions with a thermal environment (consisting e.g. internal vibrations, solvent), rectification ratios reach three orders of magnitude. We introduce decoherence and inelastic-dissipative effects phenomenologically, by using the "voltage probe" approach. We find that when $\gamma_d \lesssim v$, with $\gamma_d$ the interaction energy of electrons with the environment and $v$ the tunneling energy across the saturated link, the diode is still highly effective, though rectification ratios are cut down by a factor of 2-4 compared to the coherent limit. To further enhance rectification ratios in molecular diodes we suggest a refined design involving four orbitals, with a pair of closely spaced states at each conjugated moiety.