The Electronic Structures And Rashba Spin-orbit Coupling Of Two-dimensional Janus VSeX (X=Cl,Br,I) Monolayers And Its Heterostructures

Spin orbit coupling（SOC）provides the possibility of using electricity to regulate spin magnetic moments and plays a crucial role in the field of spin electronic devices.The two-dimensional Janus 2H-VSe X（X=Cl,Br,I）layered material with Rashba SOC effect is easily regulated by the electric field and is beneficial for circuit integration.It is expected to be applied in the next generation of electronic devices.Therefore,two-dimensional Janus 2H-VSe X（X=Cl,Br,I）has become a key research object.This paper is based on first principles,the main research work around single-layer Janus 2H-VSe X（X=Cl,Br,I）as follows:1.This article systematically elaborates on the band orbital composition,interface potential,dipole moment,electron transfer,and Rashba spin of monolayer Janus 2H-VSe X（X=Cl,Br,I）.Calculation shows that monolayer Janus 2H-VSe X（X=Cl,Br,I）show a large Rashba spin splitting in the valence band near theΓpoint(α_{VSe Cl}=0.093e V·（?）,α_{VSe Br}=0.163 e V·（?）,α_{VSe I}=0.180 e V·（?）)。Deeply investigate the effect of strain on Rashba spin splitting using a biaxial strain of-6%-6%.The results showed that compressive strain significantly improved the Rashba parameters,with-6%compressive strain resulting in a maximum increase of 4.35,3.59,and 3.70 times in the Rashba parameters of monolayer 2H-VSe Cl,2H-VSe Br,and 2H-VSe I,respectively.Rashba parametersα_R of monolayer 2H-VSe I achieved its maximum value at-6%strain,α_k-Γ/αΓ_-K’is 0.6613/0.6621 e V·（?）.Under compressive strain,the monolayer Janus 2H-VSe X（X=Cl,Br,I）exhibits coupling between Rashba SOC and hat shaped dispersion,which enhances the Rashba effect.In addition,monolayer 2H-VSe Cl and monolayer2H-VSe I underwent a nonmagnetic Rashba semiconductor to magnetic metal transition and a Rashba semiconductor to Rashba metal transition at 6%tensile strain,respectively.Monolayer 2H-VSe Br and 2H-VSe I exhibit helical band gaps under tensile strain.2.Taking the most representative monolayer 2H-VSe Br with Rashba effect as an example,study the bilayer structure of polar Janus 2H-VSe X（X=Cl,Br,I）and the Rashba effect of heterostructure s.It was found in the bilayer stacking that Rashba SOC could only exist in bilayer 2H-VSe Br with different interface atomic properties and spatially symmetric collapse.Moreover,Rashba SOC weakens in magnetic systems,confirming the competitive relationship between Rashba SOC and magnetic exchange interactions of 2H-VSe Br.Two types of Zn O/2H-VSe Br heterostructures with atomic interfaces were constructed,with I-C12 Zn O/2H-VSe Br heterostructure having the maximumα_R（0.696 e V·（?））.The Zn O/2H-VSe Br heterostructures exhibits band alignment changes in types I,II,and III.and a hat like dispersion coupled with Rashba SOC at the valence band top was observed.This special band structure is of great significance for the spin charge conversion.The strain significantly enhanced the Rashba SOC of Zn O/2H-VSe Br heterostructure,with the maximum effect of 2%Rashba spin splitting,and the Rashba parametersα_R reach a maximum of 0.842 eV·（?）.