Bipolarized Weyl semimetals and quantum crystal valley Hall effect in two-dimensional altermagnetic materials
Abstract
Magnetism and topology are two major areas of condensed matter physics. The combination of magnetism and topology gives rise to more novel physical effects, which have attracted strongly theoretical and experimental attention. Recently, the concept of altermagnetism has been introduced, characterized by a dual nature: real-space antiferromagnetism and reciprocal-space anisotropic spin polarization. The amalgamation of altermagnetism with topology may lead to the emergence of previously unobserved topological phases and the associated physical effects. In this study, utilizing a four-band lattice model that incorporates altermagnetism and spin group symmetry, we demonstrate that type-I, type-II, and type-III bipolarized Weyl semimetals can exist in altermagnetic systems. Through the first-principles electronic structure calculations, we predict four ideal two-dimensional type-I altermagnetic bipolarized Weyl semimetals Fe2WTe4 and Fe2MoZ4 (Z=S,Se,Te). More significantly, we introduce the quantum crystal valley Hall effect, a phenomenon achievable in three of these materials namely Fe2WTe4, Fe2MoS4, and Fe2MoTe4, when spin-orbit coupling is considered. Furthermore, these materials have the potential to transition from a quantum crystal valley Hall phase to a Chern insulator phase under strain. In contrast, Fe2MoSe4 remains to be a Weyl semimetal under spin-orbit coupling but is distinguished by possessing only a single pair of Weyl points. Additionally, the position, polarization, and number of Weyl points in Fe2WTe4 and Fe2MoZ4 can be manipulated by adjusting the direction of the N\'eel vector. Consequently, Fe2WTe4 and Fe2MoZ4 emerge as promising experimental platforms for investigating the distinctive physical attributes of various altermagnetic topological phases.
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