Orbital-selective spin excitation of a magnetic porphyrin

TL;DR

This study demonstrates that electron tunneling through different orbitals in a magnetic porphyrin molecule can selectively excite its spin states, with the excitation pathways influenced by orbital hybridization and localization.

Contribution

It reveals how molecular orbital selection controls spin excitation mechanisms in magnetic molecules, combining experimental STM spectra with DFT and scattering models.

Findings

Inelastic spin excitation extends beyond the iron site.

Spectral lineshape varies with orbital hybridization.

Excitation pathways depend on the selected molecular orbital.

Abstract

Scattering of electrons by localized spins is the ultimate process enabling electrical detection and control of the magnetic state of a spin-doped material. At the molecular scale, this scattering is mediated by the electronic orbitals hosting the spin. Here we report the selective excitation of a molecular spin by electrons tunneling through different molecular orbitals. Spatially-resolved tunneling spectra on iron porphyrins on Au(111) reveal that the inelastic spin excitation extends beyond the iron site. The inelastic features also change shape and symmetry along the molecule. Combining DFT simulations with a phenomenological scattering model, we show that the extension and lineshape variations of the inelastic signal are due to excitation pathways assisted by different frontier orbitals, each of them with a different degree of hybridization with the surface. By selecting the intramolecular site for electron injection, the relative weight of iron and pyrrole orbitals in the tunneling process is modified. In this way, the spin excitation mechanism, reflected by its spectral lineshape, changes depending on the degree of localization and energy alignment of the chosen molecular orbital.