Bridging Marcus–Landauer Transport Regimes in Orbital-Gated Molecular Junctions
Phys. Rev. Lett. 137, 186301 – Published 28 October, 2026
DOI: https://doi.org/10.1103/6cdn-9cnf
Abstract
Charge transport in molecular junctions is commonly described by either Marcus theory, which captures thermally activated hopping via redox processes, or Landauer formalism, which models elastic tunneling between two electrodes. However, real molecular junctions often operate in an intermediate regime between the two transport limits, requiring a comprehensive understanding. Here, we investigate orbital-gated molecular transistors fabricated by forming self-assembled monolayers of redox-active ferrocene-terminated alkanethiols on an Au bottom electrode, contacting them with a graphene top electrode and gating them through ionic media. By tuning the gate voltage to modulate the energetic alignment of the frontier molecular orbital, we observed a continuous variation of the activation energy from 3.8 to 117.8 meV. We find that the dominant transport type can be switched between Marcus-type (thermally activated) and Landauer-type (temperature-independent) behavior, as the orbital enters or exits the transmission window defined by the electrochemical potentials of the electrodes. This crossover under orbital gating is quantitatively described by the multispace density functional theory and the lifetime-broadened Marcus theory. Our orbital-gated molecular transistors bridge the hopping–tunneling transport regimes, providing a device-scale platform for controlling the dominant transport phenomena.
