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Observation of orbital pumping

Abstract

Electrons carry both spin and orbital angular momentum. The search for phenomena that generate a flow of spin angular momentum—a spin current—has led to the development of spintronics. In contrast, the orbital counterpart of spin current—an orbital current—has largely been overlooked, and the generation of an orbital current remains challenging. Here we report the observation of orbital-current generation from magnetization dynamics: orbital pumping. We show that orbital pumping in nickel/titanium bilayers injects an orbital current into the titanium layer, which we detect through the inverse orbital Hall effect. Orbital pumping is the orbital counterpart of spin pumping, a versatile and powerful mechanism for spin-current generation. Our findings could, thus, provide a promising approach for generating orbital currents and could help in the development of the orbital analogue of spintronics: orbitronics.

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Fig. 1: Orbital pumping and IOHE.
Fig. 2: Role of Ti and FM layers in charge-current generation.
Fig. 3: Charge-current spectra at various microwave powers and magnetic-field angles.
Fig. 4: Dependence of the charge current on the magnetic-field angle.
Fig. 5: Charge-current generation efficiency.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by the Japan Society for the Promotion of Science (JSPS; KAKENHI Grant Nos. 22H04964, 20H00337 and 20H02593 to K.A.), the Spintronics Research Network of Japan (grant to K.A.) and the Ministry of Education, Culture, Sports, Science and Technology’s Initiative to Establish Next-generation Novel Integrated Circuit Centers (Grant No. JPJ011438 to K.A.). H.H. is supported by a JSPS grant-in-aid for research fellowship for young scientists (Grant No. 20J20663) and JSPS (KAKENHI Grant No. 23K19037). D.G. and Y.M. acknowledge the German Research Foundation (Grant Nos. TRR 173/2-268565370-Spin+X (Project A11) and TRR 288-422213477 (Project B06)) for funding. D.G. and Y.M. gratefully acknowledge the Jülich Supercomputing Centre for providing computational resources under project jiff40.

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H.H. and S.H. fabricated the devices, collected and analysed the data, and characterized the materials. H.H. and K.A. designed the experiments. H.H., D.G., Y.M. and K.A. developed the explanation. H.H. and K.A. wrote the paper with help from D.G and Y.M. All authors discussed the results and reviewed the paper. K.A. supervised the study.

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Correspondence to Kazuya Ando.

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Nature Electronics thanks Henri Jaffrès, Pranaba Muduli and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Notes 1–7 and Figs. 1–11.

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Hayashi, H., Go, D., Haku, S. et al. Observation of orbital pumping. Nat Electron (2024). https://doi.org/10.1038/s41928-024-01193-1

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