Photoninduced Weyl half-metal phase and spin filter effect from topological Dirac semimetals

Abstract

Recently discovered Dirac semimetals (DSMs) with two Dirac nodes, such as Na${}_3$Bi and Cd${}_2$As${}_3$, are regarded to carry the ${\mathbb{Z}}_2$ topological charge in addition to the chiral charge. Here, we study the Floquet phase transition of ${\mathbb{Z}}_2$ topological DSMs subjected to a beam of circularly polarized light. Due to the resulting interplay of the chiral and ${\mathbb{Z}}_2$ charges, the Weyl nodes are not only chirality-dependent but also spin-dependent, which constrains the behaviors in creation and annihilation of the Weyl nodes in pair. Interestingly, we find a novel phase: One spinband is in Weyl semimetal phase while the other spinband is in insulator phase, and we dub it Weyl half-metal (WHM) phase. We further study the spin-dependent transport in a Dirac-Weyl semimetal junction and find a spin filter effect as a fingerprint of existence of the WHM phase. The proposed spin filter effect, based on the WHM bulk band, is highly tunable in a broad parameter regime and robust against magnetic disorder, which is expected to overcome the shortcomings of the previously proposed spin filter based on the topological edge/surface states. Our results offer a unique opportunity to explore the potential applications of topological DSMs in spintronics.

arXiv comment6 pages, 4 figures

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