Statistical analysis of electron-induced switching of a spin-crossover complex

TL;DR

This study uses low-temperature STM to analyze electron-induced spin-state switching in a specific iron complex on Ag(111), revealing the microscopic mechanism and estimating molecular orbital energies, with implications for controlling switching rates.

Contribution

It provides a detailed microscopic understanding of electron-induced spin crossover switching and estimates molecular orbital energies through experimental and theoretical comparison.

Findings

Switching rates depend on sample voltage.

Switching triggered by transient molecular charging.

Decoupling substrate enhances switching rates.

Abstract

Spin-crossover complexes exhibit two stable configurations with distinct spin states. The investigation of these molecules using low-temperature scanning tunneling microscopy has opened new perspectives for understanding the associated switching mechanisms at the single-molecule level. While the role of tunneling electrons in driving the spin-state switching has been clearly evidenced, the underlying microscopic mechanism is not completely understood. In this study, we investigate the electron-induced switching of [Fe(H$_2$B(pz)(pypz))$_2$] (pz = pyrazole, pypz = pyridylpyrazole) adsorbed on Ag(111). The current time traces show transitions between two current levels corresponding to the two spin states. We extract switching rates from these traces by analyzing waiting-time distributions. Their sample-voltage dependence can be explained within a simple model in which the switching is triggered by a transient charging of the molecule. The comparison between experimental data and theoretical modeling provides estimates for the energies of the lowest unoccupied molecular orbitals, which were so far experimentally inaccessible. Overall, our approach offers new insights into the electron-induced switching mechanism and predicts enhanced switching rates upon electronic decoupling of the molecule from the metallic substrate, for example by introducing an ultrathin insulating layer.