Single-atom electron paramagnetic resonance in a scanning tunneling microscope driven by a radiofrequency antenna at 4 K

TL;DR

This paper demonstrates efficient single-atom electron paramagnetic resonance (EPR) in a scanning tunneling microscope (STM) at 4 K using a radiofrequency antenna, enabling advanced magnetic studies of individual atoms.

Contribution

It introduces a novel RF antenna coupling method for EPR-STM that operates effectively at 4 K, allowing routine high-temperature EPR measurements and broadening experimental possibilities.

Findings

Achieved near-unity microwave coupling efficiency with RF antenna.

Demonstrated EPR-STM operation at temperatures above 4 K.

Compared different acquisition modes to optimize EPR signals.

Abstract

Combining electron paramagnetic resonance (EPR) with scanning tunneling microscopy (STM) enables detailed insight into the interactions and magnetic properties of single atoms on surfaces. A requirement for EPR-STM is the efficient coupling of microwave excitations to the tunnel junction. Here, we achieve a coupling efficiency of the order of unity by using a radiofrequency antenna placed parallel to the STM tip, which we interpret using a simple capacitive-coupling model. We further demonstrate the possibility to perform EPR-STM routinely above 4 K using amplitude as well as frequency modulation of the radiofrequency excitation. We directly compare different acquisition modes on hydrogenated Ti atoms and highlight the advantages of frequency and magnetic field sweeps as well as amplitude and frequency modulation in order to maximize the EPR signal. The possibility to tune the microwave-excitation scheme and to perform EPR-STM at relatively high temperature and high power opens this technique to a broad range of experiments, ranging from pulsed EPR spectroscopy to coherent spin manipulation of single atom ensembles.