Regulation Of Quantum Properties Of Asymmetrically Modified Ⅴ Two-dimensional Materials

Nano-materials and devices based on Group V elements are one of the key future directions in spintronics.This study focuses on the design of two-dimensional materials using first-principles calculations based on density functional theory.The main research direction is the investigation and design of spintronics materials with quantum properties and controllability,with particular emphasis on exploring materials with non-dissipative and effective massless characteristics,as well as materials exhibiting valleytronics properties.The following are the main research topics:1.Quantum anomalous Hall insulators hold tremendous potential for low-power electronic devices,and it is imperative to search for materials that exhibit both robust intrinsic ferromagnetism and nontrivial band gaps.Therefore,a two-dimensional thin film with the quantum anomalous Hall effect,namely nitrogen-oxygen asymmetrically modified Sb As film,including N-Sb As-O and N-As Sb-O configurations,was designed.The electronic properties,magnetic properties,topological properties,and optical properties of N-Sb As-O and N-As Sb-O were systematically investigated.The study demonstrates that N-Sb As-O and N-As Sb-O exhibit intrinsic ferromagnetism.The spin-orbit coupling induces a topologically nontrivial band gap of 116/147 me V in N-Sb As-O/N-As Sb-O.The presence of topologically protected edge states and quantized anomalous Hall conductivity further confirms that N-Sb As-O/N-As Sb-O are quantum anomalous Hall insulators.Moreover,the quantum properties can be modulated by applied strain and external electric fields within a certain range.N-Sb As-O and N-As Sb-O exhibit favorable optical absorption characteristics in the infrared,visible,and ultraviolet regions.These findings provide an excellent platform for the development of novel low-power spintronic devices.2.Coexistence of quantum spin Hall effect and valley Hall effect is expected in a system.Based on this,a two-dimensional thin film,namely monolayer As CH₂OH,was designed to achieve the coexistence of contrasting physical properties including valley contrast,ferroelectricity,and topological properties.The intrinsic quantum spin Hall effect in the monolayer As CH₂OH film was predicted through Z₂ topological invariant and helical edge states.The topological properties of the system exhibit robustness against strain engineering,rotation angles of ligands,and ligand modifications.The valley spin splitting,polarization,and bandgap can be effectively controlled.Monolayer As CH₂OH exhibits significant optical absorption characteristics in the visible and ultraviolet regions,making it applicable in areas such as optoelectronic detection.In summary,the study of monolayer As CH₂OH holds tremendous potential for applications in low-energy electronic devices and quantum computing.3.Utilizing valley degree of freedom as an information carrier has been a hot topic in both fundamental and applied research.Therefore,a hydrogen-nitrogen asymmetrically modified H-As Bi-N thin film was designed.The study demonstrates that it is a novel two-dimensional material with valley properties.H-As Bi-N exhibits a significant valley spin splitting in the conduction band,with a splitting value of 230 me V.The investigation of Berry curvature further confirms that H-As Bi-N is a valleytronics material with the valley Hall effect.By flipping the magnetic axis of H-As Bi-N,the structure achieves the quantum anomalous valley Hall effect.The valley contrast properties and topological properties of the system exhibit robustness against external electric fields,and the valley splitting value,valley polarization strength,and bandgap can be effectively controlled.H-As Bi-N exhibits high sensitivity in the visible and ultraviolet regions.These studies provide a promising two-dimensional valley material and present an effective approach to achieve valley polarization.4.Finally,a more novel two-dimensional material,monolayer Bi₂NH,was designed.The electronic properties,magnetic properties,valley contrast properties,topological properties,and optical properties of Bi₂NH were systematically investigated.The spin-orbit coupling induces a transition from a direct band gap to an indirect band gap,and the study of Berry curvature demonstrates that Bi₂NH can achieve spin-valley coupled valley Hall effect.By flipping the magnetic axis of Bi₂NH,the structure achieves the quantum anomalous Hall effect.The investigation of edge states and anomalous Hall conductivity further confirms that Bi2NH is a quantum anomalous Hall insulator with Chern number+1（-1）.The topological properties of the system exhibit robustness against external electric fields,and the topological bandgap can be effectively controlled.In summary,the study of Bi₂NH provides a new approach for developing electronic devices with multiple coexisting coupled characteristics.