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arXiv · 2504.19630

Non-Equilibrium Multiplet Excitations probed by the $M_{5,4}$ Branching Ratio in $3d \rightarrow 4f$ X-ray Absorption Spectroscopy

Tim Amrhein·Beyza Salantur·Ralph Püttner·Niko Pontius·Karsten Holldack·Ru-Pan Wang·Christian Schüßler-Langeheine·Martin Weinelt·Nele Thielemann-Kühn
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Abstract

We show that ultrafast electronic $4f$ multiplet transitions in terbium metal are manifested by changes in the relative spectral weight of the $M_5$ and $M_4$ X-ray absorption resonances. Our experimental results are supported by a simulation of excited multiplet spectra with atomistic calculations; they prove that the so-called third rule of Thole and van der Laan, which relates the branching ratio of the spin-orbit split resonances to the total angular momentum $J$ of the excited ion, is also valid in non-equilibrium. The presented detection scheme allows to detect $J$-changing excitation, \textit{i.e}, alterations of spin and orbital states, even in samples without net magnetization. This makes branching-ratio spectroscopy a powerful tool for the quantitative investigation of ultrafast changes in angular momentum $J$.

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Tim Amrhein, Beyza Salantur, Ralph Püttner, Niko Pontius, Karsten Holldack, Ru-Pan Wang, Christian Schüßler-Langeheine, Martin Weinelt, Nele Thielemann-Kühn. 2025-04-28. Non-Equilibrium Multiplet Excitations probed by the $M_{5,4}$ Branching Ratio in $3d \rightarrow 4f$ X-ray Absorption Spectroscopy. https://arxiv.org/abs/2504.19630

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