Two-dimensional CoSe structures: Intrinsic magnetism, strain-tunable anisotropic valleys, magnetic Weyl point, and antiferromagnetic metal state
Bo Tai, Weikang Wu, Xiaolong Feng, Yalong Jiao, Jianzhou Zhao, Yunhao Lu, Xian‐Lei Sheng, Shengyuan A. Yang
Abstract
The interplay between magnetism, band topology, and electronic correlation in low dimensions has been a fascinating subject of research. Here, we propose two-dimensional (2D) material systems which demonstrate such an interesting interplay. Based on first-principles calculations and structural search algorithms, we identify three lowest energy 2D CoSe structures, termed as the $\ensuremath{\alpha}$-, $\ensuremath{\beta}$-, and $\ensuremath{\gamma}$-CoSe. We show that $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-CoSe are two rare examples of 2D antiferromagnetic metals, which are related to their Fermi surfaces nesting features, and meanwhile, $\ensuremath{\gamma}$-CoSe is a ferromagnetic metal. They possess a range of interesting physical properties, including anisotropic valleys connected by crystalline symmetries, strain-tunable valley polarization, strain-induced metal-semiconductor and/or magnetic phase transitions, as well as topological band features such as the magnetic Weyl point and the magnetic Weyl loop. Remarkably, all the topological features here are robust against spin-orbit coupling. Some experimental aspects of our predictions have been discussed.