Tunable Weyl half-semimetals in two-dimensional iron-based materials MFeSe (M=Tl,In,Ga)

Abstract

The layered iron chalcogenide materials have attracted considerable attention recently for their exotic superconductivity at relatively high temperatures. Topological phases are, however, seldom proposed in these materials. Based on density-functional theory calculations together with symmetry analysis, 100% spin-polarized Weyl semimetals, namely Weyl half semimetals (WHSMs), are predicted in two-dimensional (2D) TlFeSe and GaFeSe monolayers, built based on FeSe monolayers. The acquired Weyl fermions are protected by a nonsymmorphic symmetry. Dissimilarly, the InFeSe monolayer is found to be a quantum anomalous Hall (QAH) insulator with a large band gap (403 meV). By tuning the magnetization direction, the monolayers can vary from a WHSM to a QAH insulator or vice versa. The phase-transition mechanism is analyzed by using an effective $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ model. Our work provides a pathway to carry out the fascinating 2D WHSMs and the QAH effect in one material which will have promising applications in not only spintronics but also topological microelectronics.