Inelastic electron tunneling spectroscopy of a Mn dimer

TL;DR

This paper investigates the inelastic electron tunneling spectroscopy of a Mn dimer using STM, highlighting unexplained large signals and the need for new models to account for observed spin excitations.

Contribution

The study identifies limitations of existing theories for symmetric Mn dimers and explores alternative mechanisms that could explain large inelastic signals.

Findings

Hyperfine coupling induces finite excitation amplitude.

Existing models fail to explain large signals in symmetric dimers.

Symmetry-breaking mechanisms may enhance excitation probabilities.

Abstract

A scanning tunneling microscope (STM) can probe the inelastic spin excitations of single magnetic atoms in a surface via spin-flip assisted tunneling. A particular and intriguing case is the Mn dimer case. We show here that the existing theories for inelastic transport spectroscopy do not explain the observed spin transitions when both atoms are equally coupled to the STM tip and the substrate. The hyperfine coupling to the nuclear spins is shown to lead to a finite excitation amplitude, but the physical mechanism leading to the large inelastic signal observed is still unknown. We discuss some other alternatives that break the symmetry of the system and allows for larger excitation probabilities.