Using scanning tunneling and electron spin resonance spectroscopy, this study reveals Kondo and ESR coexistence in single iron phthalocyanine molecules, suggesting implications for spintronic devices.
The multiplicity of orbitals in quantum systems significantly influences the competition between Kondo screening and local spin magnetization. The identification of orbital-specific processes is essential for advancing spintronic devices, as well as for enhancing the understanding of many-body quantum phenomena, but it remains a great challenge. Here, we use a combination of scanning tunneling microscopy/spectroscopy and electron spin resonance (ESR) spectroscopy to investigate single iron phthalocyanine (FePc) molecules on MgO/Ag(100). We observe the coexistence of ESR and Kondo resonance from the Fe(II) ion center at a temperature well below the Kondo temperature TK, where the magnetic moments are determined to be 1 Bohr magneton (1μB), corresponding to a spin $S=1/2$ state in either of the ESR and Kondo resonance channels. On the basis of the observed in-plane twofold symmetry in the spatial distribution of ESR linewidths, in combination with density functional theory calculations, we attribute one spin $S=1/2$ state in the degeneracy-lifted d_π orbital to the ESR channel, and the other in the highly screenable d_z² orbital to the Kondo resonance, respectively, within the framework of the $S=1$ two-channel Kondo model of an ordinary Fermi liquid.
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Chen et al. (2025) studied this question.
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