A model for the ESR-STM phenomenon

TL;DR

This paper introduces a theoretical model explaining the ESR-like signals observed in STM experiments at room temperature, highlighting the role of tip-substrate tunneling and spin states in detecting single spins.

Contribution

The model accounts for ESR signals without spin polarization of tip and substrate, matching experimental observations and predicting signal splitting under resonant ac fields.

Findings

Sharp ESR-like signal at Larmor frequency at high temperatures

Signal splitting predicted by Rabi frequency under ac field

Good agreement with experimental data

Abstract

We propose a model to account for the observed ESR-like signal at the Larmor frequency in the current noise STM experiments identifying spin centers on various substrates. The theoretical understanding of this phenomenon, which allows for single spin detection on surfaces at room temperature, is not settled for the experimentally relevant case that the tip and substrate are not spin polarized. Our model is based on a direct tip-substrate tunneling in parallel with a current flowing via the spin states. We find a sharp signal at the Larmor frequency even at high temperatures, in good agreement with experimental data. We also evaluate the noise in presence of an ac field near resonance and predict splitting of the signal by the Rabi frequency.