arXiv subjects

Bo-Wen Yu

Publications and source records attributed to Bo-Wen Yu.

5 recordsLinked to original sources

arXiv2026

Spin-valley-layer coupling with dual control via stacking and electric field in antiferromagnetic bilayer Janus YIBr

The modification and enhancement of antiferromagnetic two-dimensional semiconductor is considered crucial for realizing novel electronic properties and facilitating promising applications. For this purpose, we investigate six antiferromagnetic 2D bilayer Janus YIBr structures with different stacking variations by means of first-principles calculation and an effective low-energy model. The calculation of magnetic anisotropy energy shows that the direction of easy axis varies with different stacking. First-principles-calculated energy bands reveal that there is a Dirac relativistic dispersion relation exists in the valence band in a wide energy window of 0.3 eV at least. The calculations for spin, atom properties and Berry curvature description show that there is spin, valley and layer coupling with spin splitting, valley polarization and valley Hall and layer Hall effects can be achieved in the bilayer Janus structures. Further analyses of the effect of external electric field can be used to control spin, valley and layer of the hole near the Fermi level and to realize an anomalous valley Hall effect. These can be useful in future exploration for novel properties, control methods and more functionalities in bilayer Janus structures.

cond-mat.mes-hall↗

arXiv2024

Spin-split flat bands at the band edge and two-dimensional hole gases towards quantum Hall effect in altermagnetic CoF$_2$

Altermagnetic phase is recently found as a new magnetic phase in addition to the conventional collinear spin orders, and great efforts have been made to explore novel effects and potential applications in such materials. Here, we show that there are robust altermagnetic spin-split flat bands near the valence band edge in rutile CoF$_2$ through first-principles investigation. It is uncovered that the magnetic moments can remain in the z axis because of the magnetocrystalline energy due to the spin-orbits coupling and the spin orientation can be made more stable by magnetic field applied in the xy plane. We describe the spin-dependent band structure (including the flat bands) near the Fermi level by a spin-resolved effective low-energy model, and reveal that they can host spin-dependent two-dimensional hole gases. Importantly, we find spin-dependent quantum Hall effects in the two-dimensional hole gases by applying the magnetic field in the xy plane, and then explore the dependence of Hall conductivity and Hall resistance on the Fermi level and the magnetic field (both magnitude and direction) and related longitudinal carrier transport properties.

cond-mat.mtrl-sci↗

arXiv2024

Dirac-Rashba fermions and quantum valley Hall insulators in graphene-based 2D heterostructures

It is highly desirable to modify and improve the Dirac electron system of graphene for novel electronic properties and promising applications. For this purpose, we study 2D heterostructures consisting of graphene and monolayer TMDs by means of first-principles calculation and effective low-energy hamiltonian model. We determine the model parameters by fitting with the first-prinples bands. MoSe$_2$ and WSe$_2$ are chosen in order to align the Dirac cones of graphene with the intrinsic Fermi levels of the TMDs. It is found that the Dirac energy bands of graphene are modified, but the linear band dispersion near the cones is kept. It is shown that the effective low-energy model hosts Dirac-Rashba feimions in the WSe$_2$/graphene and MoSe$_2$/graphene/WSe$_2$, and there is quantum valley Hall effect in these graphene-based 2D heterostructures. Our further analyses indicate that there are strong interactions between the orbitals and spins especially near the K and K' points. These can be useful in further exploration for novel properties and more functionalities in 2D heterostructures.

cond-mat.mes-hall↗

arXiv2023

Unconventional Rashba spin splitting and persistent spin helices based on SU(2) symmetry in PtSe$_2$ nanoribbons

2D materials can host interesting physics and have important applications in various fields. Recent experiment shows that monolayer PtSe$_2$ nanoflakes with neutral zigzag edges are stable. Here, we study semiconducting stoichiometric PtSe$_2$ nanoribbons with the stable neutral zigzag edges (with $N$ describing different nanoribbon width) through combining detailed first-principles investigation with low-energy model analysis. Our careful analysis of first-principles conduction and valence bands (with the spin-orbits coupling taken into account) indicates that the low-energy bands assume relativistic energy dispersion in an energy window of [-0.2 eV, 0.2eV] (at least) and have large unconventional Rashba spin splitting (for even $N$). Furthermore, it is demonstrated that the low-energy bands can be well described by an effective one-dimensional electron model and the semiconductor gap will remain finite even for large $N$. Most importantly, it is shown that there exists SU(2) spin symmetry in both of the conduction and valence bands for each edge, which implies persistent spin helices (in the spin xy plane) and spin-conserving carrier transport. When the inter-edge interaction becomes weak ($N$ is large enough), a nearly-perfect Dirac fermion system can be achieved through combining the valence and conduction bands. Thus we realize unconventional Rashba splitting, double SU(2) spin symmetry, persistent spin helices/textures, and pure Dirac fermion systems in stable monolayer PtSe$_2$ nanoribbons.

cond-mat.mes-hall↗

arXiv2022

Possible structural and bond reconstruction in 2D ferromagnetic semiconductor VSe2 under uniaxial stress

2D semiconducting transition metal dichalcogenides have been used to make high-performance electronic, spintronic, and optoelectronic devices. Recently, room-temperature ferromagnetism and semiconducting property were found in 2D VSe$_2$ nanoflakes (mechanically exfoliated onto silicon substrates capped with a oxide layer) and are attributed to the stable 2H-phase of VSe$_2$ in the 2D limit. Here, our first-principles investigation show that a metastable semiconducting H' phase can be formed from the H VSe2 monolayer and some other similar when these 2D H-phase materials are under uniaxial stress or uniaxial strain. For the uniaxial stress (uniaxial strain) scheme, the H' phase will become lower in total energy than the H phase at the transition point. The calculated phonon spectra indicate the dynamical stability of the H' structures of VSe$_2$, VS$_2$, and CrS$_2$, and the path of phase switching between the H and H' VSe$_2$ phases is calculated. For VSe$_2$, the H' phase has stronger ferromagnetism and its Currier temperature can be substantially enhanced by applying uniaxial stress or strain. Spin-resolved electronic structures, energy band edges, and effective carrier masses for both of the H and H' phases can be substantially changed by the applied uniaxial stress or strain, leading to huge effective masses near the band edge of the strained H' phase. Analysis indicated that the largest bond length difference between the H' and H phases can reach -19\% for the Se3-Se3' bond, and there is noticeable covalence for the Se3-Se3' bond, which switches the valence of the nearby V atoms, leading to the enhanced ferromagnetism. Therefore, structural and bond reconstruction can be realized by applying uniaxial stress in 2D ferromagnetic H VSe$_2$ and some other similar. These can be useful to seeking more insights and phenomena in such 2D materials for potential applications.

cond-mat.mtrl-sci↗