Electron spin secluded inside a bottom-up assembled standing metal-molecule nanostructure

TL;DR

This study demonstrates a method to create a standing metal-molecule nanostructure with a secluded electron spin, enabling detailed quantum effect investigations and tunable interactions with the substrate at millikelvin temperatures.

Contribution

The paper introduces a novel approach to lift molecules into a standing position on a metal surface, significantly reducing electron-electron coupling and enabling spin isolation and tunability.

Findings

The nanostructure exhibits an $S=1/2$ spin screened by substrate electrons.

The Kondo temperature of the system is approximately 291 mK.

The exchange coupling can be tuned via STM tip interaction.

Abstract

Artificial nanostructures, fabricated by placing building blocks such as atoms or molecules in well-defined positions, are a powerful platform in which quantum effects can be studied and exploited on the atomic scale. Here, we report a strategy to significantly reduce the electron-electron coupling between a large planar aromatic molecule and the underlying metallic substrate. To this end, we use the manipulation capabilities of a scanning tunneling microscope (STM) and lift the molecule into a metastable upright geometry on a pedestal of two metal atoms. Measurements at millikelvin temperatures and magnetic fields reveal that the bottom-up assembled standing metal-molecule nanostructure has an $S = \frac{1}{2}$ spin which is screened by the substrate electrons, resulting in a Kondo temperature of only $291 \pm 13$ mK. We extract the Land\'e $g$-factor of the molecule and the exchange coupling $J\rho$ to the substrate by modeling the differential conductance spectra using a third-order perturbation theory in the weak coupling and high-field regimes. Furthermore, we show that the interaction between the STM tip and the molecule can tune the exchange coupling to the substrate, which suggests that the bond between the standing metal-molecule nanostructure and the surface is mechanically soft.