Negative differential conductance in triangular molecular assemblies

TL;DR

This paper demonstrates a molecular device exhibiting negative differential conductance due to electron correlations, using a triangular molecular assembly on a superconducting substrate, with potential for scalable nanoelectronics.

Contribution

The study introduces a molecular-scale NDC device with controllable electronic properties, supported by experimental observations and theoretical modeling, independent of superconductivity.

Findings

Robust NDC observed between 0.7-0.9 V

Coulomb rings and NDC regions visualized via conductance mapping

Theoretical model reproduces experimental NDC from electron correlations

Abstract

We report the creation and characterization of a molecular-scale negative differential conductance (NDC) device by assembling a triangular trimer of 4,5,9,10-tetrabromo-1,3,6,8-tetraazapyrene (TBTAP) molecules on a superconducting Pb(111) substrate. Using low-temperature scanning tunneling spectroscopy, we observe robust NDC behavior manifesting as a decrease in current with increasing voltage between 0.7-0.9 V arising from the interplay of Coulomb blockade and strong inter-molecular capacitive coupling within the molecular cluster. Gate-controlled charging and discharging processes are directly visualized via two-dimensional differential conductance mapping, which reveals the emergence of Coulomb rings and spatial regions of NDC. Theoretical modeling using a three-impurity Anderson model and master equation approach quantitatively reproduces the experimental observations and demonstrates that the NDC emerges purely from electron correlations, independent of the underlying superconductivity. By tuning the geometry to a hexamer structure, we further show that cluster topology provides versatile control over electronic properties at the molecular scale. These results establish a functional platform for implementing multifunctional molecular devices and highlight a strategy toward programmable and scalable nanoelectronics.