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Altermagnetism exhibits unique physical properties such as spin-momentum locking, anomalous Hall effect, nontrivial topological phase, and giant magnetoresistance. Among all the predicted candidates, several room-temperature altermagnets are suggested to host significant potential applications. Ru O 2 has been proposed as the most promising candidate. However, recently, there is intense debate about whether Ru O 2 exhibits magnetic order or not. Experiments by several different technologies claim the collinear magnetic order and spin-splitting-induced effects. However, very recent muon spin resonance (μSR) results reveal no magnetic order in Ru O 2 , which indicates that the time-reversal symmetry is not broken. Direct observation of the high-resolution bulk band structure is absent to date but essential to investigate the electronic structure of Ru O 2 . In this study, utilizing soft x-ray angle-resolved photoemission spectroscopy, we report systematic direct experimental observation of bulk band structure of Ru O 2 .
Lin et al. (Wed,) studied this question.