Addressing sub-meV interactions and multi-orbital configurations with X-ray absorption spectroscopy

DIPC Seminars

Speaker

Fabio Donati
Center for Quantum Nanoscience, Institute for Basic Science (IBS), Department of Physics, Ewha Womans University, Republic of Korea

When

2024/02/23
12:00

Place

Donostia International Physics Center (in person seminar)

Host

Deung-Jang Choi

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X-ray absorption spectroscopy (XAS) is a well-established technique to measure magnetic moments, crystal field splittings, as well as intra- and inter-atomic interactions in magnetic systems. However, accurately unraveling low-energy physics phenomena and orbital selective information from the spectra is challenging in hybridized systems such as metal-organic complexes [1] or single atoms on surfaces [2]. To address this, we propose two complementary approaches. With the first one, we combine machine learning and multiplet calculations to optimize and enhance the accuracy of XAS fitting. We demonstrate its effectiveness by applying this method on XAS data from vanadyl and titanyl phthalocyanine layers on Ag (100) and by comparing the results with Density Functional Theory (DFT) [3,4]. 
We apply this method to a nickel-based supramolecular metal complex on a van der Waals superconductor. Scanning tunneling microscopy, XAS, and DFT calculations reveal a non collinear magnetic ground states emerging from antiferromagnetic interactions, which spatially modulate the instentity of the Yu-Shiba-Rusinov bands. Machine-learning assisted multiplet calculations effectively interpret the X-ray spectra, unveiling an exchange interaction energy of 0.2 meV [5]. These findings confirm the efficacy of our approach in investigating sub-meV interactions using high-energy X-ray probes, providing valuable insights for optimizing metal-organic complexes in molecular spintronics and quantum computing. Finally, I will present the use of XAS to probe the magnetism of rare earth atoms on surfaces with orbital sensitivity. Exploiting the optical selection rules of the X-ray absorption, we addressed the electron occupation and magnetic moments of Gd, Ho and Nd atoms with orbital sensitivity. Combining our results with density functional  theory, we fully map the electronic configuration of the lanthanide atoms and identify the transfer of charge ocurring from individual orbitals [2]. Our results open new possibilities to address the electron configuration of single atom magnets and tailor their magnetic states.

References:
[1] J. Lobo-Checa et al.,https://doi.org/10.48550/arXiv.2209.14994.
[2] A. Singha et al., ACS Nano 15, 16162 (2021).
[3] J. Lee at al., https://doi.org/10.48550/arXiv.2309.16415.
[4] K. Noh et al., Nanoscale Horiz., 8, 624 (2023).
[5] V. Vaňo et al.,https://doi.org/10.48550/arXiv.2309.02537.