Lv Ming-Hao, Li Chang-Ming, Sun Wei-Feng
Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, School of Electrical and Electronic Engineering, Harbin University of Science and Technology, Harbin 150080, China.
School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore.
Nanomaterials (Basel). 2022 Jan 24;12(3):382. doi: 10.3390/nano12030382.
Phonon and spintronic structures of monolayered Janus vanadium-dichalcogenide compounds are calculated by the first-principles schemes of pseudopotential plane-wave based on spin-density functional theory, to study dynamic structural stability and electronic spin-splitting due to spin-orbit coupling (SOC) and spin polarization. Geometry optimizations and phonon-dispersion spectra demonstrate that vanadium-dichalcogenide monolayers possess a high enough cohesive energy, while VSTe and VTe monolayers specially possess a relatively higher in-plane elastic coefficient and represent a dynamically stable structure without any virtual frequency of atomic vibration modes. Atomic population charges and electron density differences demonstrate that V-Te covalent bonds cause a high electrostatic potential gradient perpendicular to layer-plane internal VSTe and VSeTe monolayers. The spin polarization of vanadium 3-orbital component causes a pronounced energetic spin-splitting of electronic-states near the Fermi level, leading to a semimetal band-structure and increasing optoelectronic band-gap. Rashba spin-splitting around G point in Brillouin zone can be specifically introduced into Janus VSeTe monolayer by strong chalcogen SOC together with a high intrinsic electric field (potential gradient) perpendicular to layer-plane. The vertical splitting of band-edge at K point can be enhanced by a stronger SOC of the chalcogen elements with larger atom numbers for constituting Janus V-dichalcogenide monolayers. The collinear spin-polarization causes the band-edge spin-splitting across Fermi level and leads to a ferrimagnetic order in layer-plane between V and chalcogen cations with higher and spin densities, respectively, which accounts for a large net spin as manifested more apparently in VSeTe monolayer. In a conclusion for Janus vanadium-dichalcogenide monolayers, the significant Rashba splitting with an enhanced K-point vertical splitting can be effectively introduced by a strong SOC in VSeTe monolayer, which simultaneously represents the largest net spin of 1.64 (/2) per unit cell. The present study provides a normative scheme for first-principles electronic structure calculations of spintronic low-dimensional materials, and suggests a prospective extension of two-dimensional compound materials applied to spintronics.
基于自旋密度泛函理论的赝势平面波第一性原理方法，计算了单层Janus钒二硫属化合物的声子和自旋电子结构，以研究动态结构稳定性以及自旋轨道耦合（SOC）和自旋极化引起的电子自旋分裂。几何优化和声子色散谱表明，钒二硫属化合物单层具有足够高的内聚能，而VSTe和VTe单层特别具有相对较高的面内弹性系数，并且代表了没有任何原子振动模式虚频的动态稳定结构。原子布居电荷和电子密度差表明，V-Te共价键在垂直于VSTe和VSeTe单层平面内部产生高静电势梯度。钒3轨道分量的自旋极化导致费米能级附近电子态明显的能量自旋分裂，导致半金属能带结构并增加光电子带隙。通过强硫属元素SOC以及垂直于层平面的高本征电场（势梯度），可以将布里渊区G点附近的Rashba自旋分裂专门引入Janus VSeTe单层。对于构成Janus V-二硫属化合物单层的原子序数较大的硫属元素，更强的SOC可以增强K点处能带边缘的垂直分裂。共线自旋极化导致能带边缘自旋分裂穿过费米能级，并在V和硫属阳离子之间的层平面中分别导致具有较高 和 自旋密度的亚铁磁序，这解释了在VSeTe单层中更明显表现出的大净自旋。对于Janus钒二硫属化合物单层的结论是，通过VSeTe单层中的强SOC可以有效地引入具有增强的K点垂直分裂的显著Rashba分裂，其同时代表每个晶胞最大净自旋为1.64（/2）。本研究为自旋电子低维材料的第一性原理电子结构计算提供了规范方案，并为二维复合材料应用于自旋电子学提出了前瞻性扩展。
