Room-temperature magnetic higher-order topological states in two-dimensional transition metal dichalcogenides and dihalogenides

Higher-order topological insulators (HOTIs) have attracted significant interest in recent years due to their unique properties, but the material realization is mainly limited to nonmagnetic systems. In this work, through tight-binding modeling and first-principles calculations, we reveal the experimentally synthesized two-dimensional (2D) $\mathrm{VS}{\mathrm{e}}_{2}$ as an example of a room-temperature magnetic HOTI. The nontrivial nature is characterized by an inverted band feature with a large gap and spin-polarized corner states with quantized fractional charge. We demonstrate that the topological corner states are robust against magnetization canting, defects, and strain, suggesting the great potential for experimental detection. Remarkably, the magnetic HOTI phase can be extended to other 2D dichalcogenides and dihalogenides, including $\mathrm{V}{X}_{2}, \mathrm{Sc}{{X}^{\ensuremath{'}}}_{2}, \mathrm{Y}{{X}^{\ensuremath{'}}}_{2}, \mathrm{Ru}{{X}^{\ensuremath{'}}}_{2}$ ($X=\mathrm{S}$, Se, Te; ${X}^{\ensuremath{'}}=\mathrm{Cl}$, Br, I) as well as their Janus structures. Our work not only provides a series of promising candidates for room-temperature magnetic HOTIs, but also sheds light on future design and regulation of novel quantum states for real applications.