Manipulating different degrees of freedom of electrons plays a key role in building modern electronic devices. The valley pseudospin is one of the emerging degrees of freedom beyond charge and spin of carriers. The concepts of ferrovalley semiconductor, half-valley metal and quasi-half-valley metal with intrinsic spontaneous valley polarization have been proposed. In analogy to ferromagnetic metal in spintronics, we propose the concept of ferrovalley metal with both electrons and hole carriers, where the two valleys are both metallic. By analogizing spin gapless semiconductor, we also propose the concept of the valley gapless semiconductor, where both electron and hole can be fully valley polarized. These new concepts greatly enrich the understanding of valley electronics, which can accelerate its application in the field of information processing and storage. For more details, please refer to the article entitled “Proposal for valleytronic materials: Ferrovalley metal and valley gapless semiconductor” by San-Dong Guo, et al. [Front. Phys. 19(2), 23302 (2024)]. [Photo credits: San-Dong Guo at Xi’an University of Posts and Telecommunications]
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