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Exploring two-dimensional valleytronic crystals with large valley-polarized state is of considerable importance due to the promising applications in next-generation information related devices. Here, we show first-principles evidence that single-layer NbX2 (X = S, Se) is potentially the long-sought two-dimensional valleytronic crystal. Specifically, the valley-polarized state is found to occur spontaneously in single-layer NbX2, without needing any external tuning, which arises from their intrinsic magnetic exchange interaction and inversion asymmetry. Moreover, the strong spin-orbit coupling strength within Nb-d orbitals renders their valley- polarized states being of remarkably large (NbS2 ~ 156 meV/NbSe2 ~ 219 meV), enabling practical utilization of their valley physics accessible. In additional, it is predicted that the valley physics (i.e., anomalous valley Hall effect) in single-layer NbX2 is switchable via applying moderate strain. These findings make single-layer NbX2 tantalizing candidates for realizing high-performance and controllable valleytronic devices.

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Publication history

Received: 16 July 2020
Revised: 24 August 2020
Accepted: 15 September 2020
Published: 01 March 2021
Issue date: March 2021

Copyright

© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature

Acknowledgements

This work is supported by the National Natural Science Foundation of China (No. 11804190), Shandong Provincial Natural Science Foundation of China (Nos. ZR2019QA011 and ZR2019MEM013), Shandong Provincial Key Research and Development Program (Major Scientific and Technological Innovation Project) (No. 2019JZZY010302), Shandong Provincial Key Research and Development Program (No. 2019RKE27004), Qilu Young Scholar Program of Shandong University, and Taishan Scholar Program of Shandong Province.

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Reprints and Permission requests may be sought directly from editorial office.
Email: nanores@tup.tsinghua.edu.cn

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