SrCu2(BO3)2 (SCBO) is a paradigmatic realization of the Shastry-Sutherland model, hosting geometrically frustrated spin dimers and a variety of quantum magnetic phases and phenomena. Although its magnetic properties have been extensively studied, the high-energy electronic excitations that determine the crystal-field environment and Cu-O hybridization have remained largely unexplored. Here we combine Cu L3-edge resonant inelastic x-ray scattering (RIXS), broadband optical spectroscopy, and electronic-structure calculations to determine the relevant local and interband excitation energy scales in SCBO. RIXS resolves a well-defined manifold of localized Cu2+ d-d excitations between 1.8 and 2.4 eV, whose energies and polarization dependence are well reproduced by multireference quantum-chemistry calculations. In contrast, optical spectroscopy identifies charge-transfer excitations with an absorption onset near 1.2-1.6 eV and a broader higher-energy structure around 4.5 eV, which are qualitatively captured by DFT+U calculations. Taken together, these results define the characteristic energy scales of d-d and CT excitations, offering quantitative benchmarks for computational frameworks and providing essential input for refining superexchange-based magnetic models of this prototypical frustrated quantum antiferromagnet.
@article{arxiv.2605.07862,
title = {Electronic excitations in the Shastry-Sutherland compound SrCu$_2$(BO$_3$)$_2$},
author = {Tariq Leinen and Ola K. Forslund and Eugenio Paris and Nicola Colonna and Marco Caputo and Johan Chang and Gabriel Nagamine and Takashi Tokushima and Conny Såthe and Pascal Puphal and Jeremie Teyssier and Thorsten Schmitt and Nikolay A. Bogdanov and Maria Daghofer and Adrian L. Cavalieri and Flavio Giorgianni},
journal= {arXiv preprint arXiv:2605.07862},
year = {2026}
}