Altermagnets, which exhibit the advantages of both antiferromagnets and ferromagnets, have attracted significant attention recently. Among them, ruthenium dioxide (RuO2), a prototypical altermagnet candidate, is under intensive debate on its magnetic order and altermagnetic characters. In this work, we provide a comprehensive study of the spin-to-charge conversion in epitaxial RuO2 thin films with various orientations and fabrication methods. By utilizing thermal spin injections from a ferrimagnetic insulator, we unambiguously reveal a negative spin Hall angle for RuO2, which is opposite to all the previous reports using ferromagnetic metals. Most importantly, we observe robust anisotropic spin-to-charge conversion in RuO2, with voltage ratios of 30% for the (100)- and (110)-orientations and 40% for the (101)-orientations. The ratio remains consistent across RuO2 films fabricated by sputtering, pulsed laser deposition, and molecular-beam epitaxy. These results conclusively show a robust and anisotropic spin Hall effect in RuO2 with the absence of altermagnetic spin-splitting contributions. Our study provides crucial insights and advances the understanding of spin-to-charge conversions in emerging materials with low crystal symmetries.
@article{arxiv.2503.07985,
title = {Absence of transport altermagnetic spin-splitting effect in RuO2},
author = {Yu-Chun Wang and Zhe-Yu Shen and Chia-Hsi Lin and Wei-Chih Hsu and You-Sheng Chen and Yi-Ying Chin and Akhilesh Kr. Singh and Wei-Li Lee and Chien-Te Chen and Ssu-Yen Huang and Danru Qu},
journal= {arXiv preprint arXiv:2503.07985},
year = {2026}
}