Electron spin spectroscopy of single TEMPO dimers coupled via interfering tunneling currents

TL;DR

This study demonstrates electron spin resonance detection in individual TEMPO dimers using ESR-STM, revealing interactions caused by interfering tunneling pathways, a novel mechanism for single-molecule ESR measurement.

Contribution

First demonstration that tunneling via two spins can be used as a mechanism in ESR-STM for detecting single-molecule electron spins.

Findings

Detected ESR in individual TEMPO dimers.

Identified exchange and Dzyaloshinskii-Moriya interactions.

Established tunneling via two spins as a valid ESR-STM mechanism.

Abstract

We report the detection of electron spin resonance (ESR) in individual dimers of the stable free radical 2,2,6,6-tetramethyl-piperidine-1-oxyl (TEMPO). ESR is measured by the current fluctuations in a scanning tunnelling microscope (ESR-STM method). The multi-peak power spectra, distinct from macroscopic data, are assigned to dimers having exchange and Dzyaloshinskii-Moriya interactions in presence of spin-orbit coupling. These interactions are generated in our model by interfering electronic tunneling pathways from tip to sample via the dimer's two molecules. This is the first demonstration that tunneling via two spins is a valid mechanism of the ESR-STM method.