Shifting the Voltage Drop in Electron Transport through a Single Molecule

TL;DR

This study investigates how the electrostatic potential change in a Mn-porphyrin molecule affects electron transport and Kondo resonance inversion in STM measurements, revealing the influence of molecular relaxation.

Contribution

It demonstrates that small geometric relaxations can cause voltage drop shifts and inversion of Kondo resonance in single-molecule electron transport.

Findings

Zero-bias Kondo resonance observed in differential conductance spectra.

Inversion of the spectrum occurs upon STM tip contact due to electrostatic potential change.

Small geometric relaxation significantly alters the voltage drop in the molecule.

Abstract

A Mn-porphyrin was contacted on Au(111) in a low-temperature scanning tunneling microscope (STM). Differential conductance spectra show a zero-bias resonance that is due to an underscreened Kondo effect according to many-body calculations. When the Mn center is contacted by the STM tip, the spectrum appears to invert along the voltage axis. A drastic change in the electrostatic potential of the molecule involving a small geometric relaxation is found to cause this observation.