Shifting the Voltage Drop in Electron Transport Through a Single Molecule

Area of Science:

• Surface science
• Condensed matter physics
• Quantum chemistry

Background:

• The Kondo effect describes the interaction between conduction electrons and localized magnetic moments.
• Manganese-porphyrin molecules are of interest due to their unique electronic and magnetic properties.
• Scanning tunneling microscopy (STM) is a powerful tool for probing electronic states at the single-molecule level.

Purpose of the Study:

• To investigate the Kondo effect in a single manganese-porphyrin molecule contacted by an STM tip.
• To understand the influence of electrostatic potential and geometric relaxation on the Kondo resonance.
• To correlate experimental observations with theoretical many-body calculations.

Main Methods:

• Low-temperature scanning tunneling microscopy (LT-STM) was used to contact a manganese-porphyrin molecule on a gold(111) surface.
• Differential conductance (dI/dV) spectroscopy was performed to probe the electronic states.
• Many-body calculations were employed to interpret the experimental results.

Main Results:

• A zero-bias resonance, indicative of an underscreened Kondo effect, was observed in the differential conductance spectra.
• Contacting the manganese center with the STM tip led to an inversion of the Kondo resonance along the voltage axis.
• A significant change in the molecule's electrostatic potential, coupled with minor geometric relaxation, was identified as the cause for the spectral inversion.

Conclusions:

• The study demonstrates the feasibility of observing and manipulating the Kondo effect in single manganese-porphyrin molecules.
• The observed spectral inversion provides direct evidence for the strong influence of local electrostatic potential on molecular Kondo physics.
• This work highlights the interplay between electronic, magnetic, and structural properties at the single-molecule level.