arXiv subjects

Jiang-Long Wang

Publications and source records attributed to Jiang-Long Wang.

8 recordsLinked to original sources

arXiv2026

On the origin of diverse interlayer charge redistribution in transition-metal dichalcogenides

The interlayer quasi-chemical-bonding (QCB) interactions of two-dimensional (2D) layered materials promote the research field of interlayer-engineering and cause interlayer charge density redistributions (ICDRs). The ICDRs have been reported experimentally and theoretically, which show different redistributions, e.g., accumulation, depletion, or a more complicated behavior. The underlying mechanism for the different ICDRs remain to be elucidated. In the current work, via a systematic theoretical study of the ICDRs of transition metal dichalcogenides with different number of d-electrons filling (d^0 TiS2, d^1 NbS2, and d^2 MoS2) in T and H phases, we reveal three mechanisms based on the coexistence of different types of interlayer QCB interactions. Mechanism (1) is from a competition between two types of interlayer interactions: namely, the interlayer interaction between fully occupied energy levels (in short: o-o interaction) depletes electrons in the overlap region while that between occupied and empty levels (o-e interaction) promotes electron accumulation; and the competition between them leads to that the d^0 TiS2 tends to electron accumulation in T phase than in H phase. Mechanism (2), the interlayer interaction between half-filled levels (h-h interaction) promotes the electron accumulation of d^1 NbS2. Mechanism (3), the interlayer interaction of multiple filled-levels of d^2 MoS2 (namely, the multi-level o-o interaction) leads to a more complicated ICDR. The current study provides a unified understanding to the different ICDRs of van der Waals materials and paves the way for further exploration of their electronic properties and applications.

cond-mat.mtrl-sci↗

arXiv2025

Anisotropic Schottky-barrier-height in high-symmetry 2D WSe$_2$: Momentum-space anisotropy

It is usually supposed that only low-symmetry two-dimensional (2D) materials exhibit anisotropy, here we show that high-symmetry 2D semiconductors can show significant anisotropy in momentum space due to the band structure anisotropy in k-space. The basic reason is that different k-points in the Brillouin zone have different symmetry. Using 2D semiconductor WSe$_2$ as the example, we construct lateral heterostructures with zigzag and armchair connections to 2D metal NbSe$_2$, and the electronic structure and contact characteristics of these two connections are analyzed. It is found that both connections exhibit p-type Schottky barrier height (SBH) but the sizes of SBH are very different (of 0.03 eV and 0.50 eV), mainly because the band-edge energies of WSe$_2$ are different along the two mutually perpendicular directions in momentum space. There are two factors contributing to the SBH anisotropy: one is the different interface structure and the other is the band edge anisotropy of the 2D semiconductor WSe$_2$. Since the two interface structures give only a difference in interface potential change by less than 0.1 eV, the SBH variation of ~0.47 eV is mainly from the band structure anisotropy in momentum-space. So, high-symmetry 2D materials may exhibit highly anisotropic electronic states in momentum space and this affects the transport properties. Our current work extends the research field of 2D material anisotropy to 2D materials with high real-space symmetry, thus greatly expands the candidate materials for anisotropic studies and provides new guidance for optimizing the performance of 2D material devices via controlling transport directions.

cond-mat.mtrl-sci↗

arXiv2024

Unified understanding to the rich electronic-structure evolutions of 2D black phosphorus under pressure

The electronic structure evolutions of few-layer black phosphorus (BP) under pressure shows a wealth of phenomena, such as the nonmonotonic change of direct gap at the Γ point, the layer-number dependence, and the distinct responses to normal and hydrostatic pressures. A full and unified understanding to these rich phenomena remains lacking. Here, we provide a unified understanding from the competition between interlayer quasi-bonding (QB) interactions and intralayer chemical bonding interactions. The former decreases while the latter increases the band gap under pressure and the origin can be correlated to different combinations of inter- and intra-layer antibonding or bonding interactions at the band edges. More interestingly, the interlayer QB interactions are a coexistence of two categories of interactions, namely, the coexistence of interactions between bands of the same occupancy (occupied-occupied and empty-empty interactions) and of different occupancies (occupied-empty interaction); and, the overall effect is a four-level interaction, which explains the anomalous interlayer-antibonding feature of the conduction band edge of bilayer BP. Our current study lay the foundation for the electronic structure tuning of two-dimensional (2D) BP, and, our analysis method for multi-energy-level interactions can be applied to other 2D semiconductor homo- and hetero-structures that have occupied-empty interlayer interactions.

cond-mat.mtrl-sci↗

arXiv2023

Momentum matching and band-alignment type in van der Waals heterostructures: Interfacial effects and materials screening

Momentum-matched type II van der Waals heterostructures (vdWHs) have been designed by assembling layered two-dimensional semiconductors (2DSs) with special band-structure combinations - that is, the valence band edge at the Gamma point (the Brillouin-zone center) for one 2DS and the conduction band edge at the Gamma point for the other [Ubrig et al., Nat. Mater. 19, 299 (2020)]. However, the band offset sizes, band-alignment types, and whether momentum matched or not, all are affected by the interfacial effects between the component 2DSs, such as the quasichemical-bonding (QB) interaction between layers and the electrical dipole moment formed around the vdW interface. Here, based on density-functional theory calculations, first we probe the interfacial effects (including different QBs for valence and conduction bands, interface dipole, and, the synergistic effects of these two aspects) on band-edge evolution in energy and valley (location in the Brillouin zone) and the resulting changes in band alignment and momentum matching for a typical vdWH of monolayer InSe and bilayer WS2, in which the band edges of subsystems satisfy the special band-structure combination for a momentum-matched type II vdWH. Then, based on the conclusions of the studied interfacial effects, we propose a practical screening method for robust momentum-matched type II vdWHs. This practical screening method can also be applied to other band alignment types. Our current study opens a way for practical screening and designing of vdWHs with robust momentum-matching and band alignment type.

cond-mat.mtrl-sci↗

arXiv2021

Interlayer Quasi-Bonding Interactions in 2D Layered Materials: A Classification According to the Occupancy of Involved Energy Bands

Recent studies have revealed that the interlayer interaction in two-dimensional (2D) layered materials is not simply of van der Waals character but could coexist with quasi-bonding character. Here we classify the interlayer quasi-bonding interactions into two main categories (I: homo-occupancy interaction, II: hetero-occupancy interaction) according to the occupancy of the involved energy bands near the Fermi level. Then we investigate the quasi-bonding-interaction-induced band structure evolution of several representative 2D materials based on density functional theory calculations. Further calculations confirm that this classification is applicable to generic 2D layered materials and provides a unified understanding of the total strength of interlayer interaction, which is a synergetic effect of the van der Waals attraction and the quasi-bonding interaction. The latter is stabilizing in main category II and destabilizing in main category I. Thus, the total interlayer interaction strength is relatively stronger in category II and weaker in category I.

cond-mat.mtrl-sci↗

arXiv2021

Hole- and electron-injection driven phase transitions in transition metal dichalcogenides and beyond: A unified understanding

The phase transitions among polymorphic two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted increasing attention for their potential in enabling distinct functionalities in the same material for making integrated devices. Electron-injection to TMDs has been proved to be a feasible way to drive structural phase transition from the semiconducting H-phase to the semimetal dT-phase. In this contribution, based on density-functional theory (DFT) calculations, firstly we demonstrate that hole-injection drives the transition of the H-phase more efficiently to the metallic T-phase than to the semimetallic dT-phase for group VI-B TMDs (MoS2, WS2, and MoSe2, etc.). The origin can be attributed to the smaller work function of the T-phase than that of the dT-phase. Our work function analysis can distinguish the T and dT phases quantitatively while it is challenging for the commonly used crystal field splitting analysis. In addition, our analysis provides a unified understanding for both hole- and electron-injection induced phase transitions for 2D materials beyond TMDs, such as the newly synthesized MoSi2N4 family. Moreover, the hole-driven T-phase transition mechanism can explain the recent experiment of WS2 phase transition by hole-doping with yttrium (Y) atoms. Using 1/3 Y-doped WS2 and MoSe2 as examples, we show that the Mo and W valency increases to 5+. These above findings open up an avenue to obtain the metallic T-phase, which expands the possible stable phases of 2D materials.

cond-mat.mtrl-sci↗

arXiv2015

Localization and Orbital Selectivity in Iron-Based Superconductors with Cu Substitution

We study an inhomogeneous three-orbital Hubbard model for the Cu-substituted iron pnictides using an extended real-space Green's function method combined with density functional calculations. We find that the onsite interactions of the Cu ions are the principal determinant of whether an electron dopant or a hole dopant is caused by the Cu substitution. It is found that the Cu substitution could lead to a hole doping when its onsite interactions are smaller than a critical value, as opposed to an electron doping when the interactions of Cu ions are larger than the critical value, which may explain why the effects of Cu substitution on the carrier density are entirely different in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$. We also find that the effect of a doping-induced disorder is considerable in the Cu-substituted iron pnictides, and its cooperative effect with electron correlations contributes to the orbital-selective insulating phases in NaFe$_{1-x}$Cu$_x$As and Ba(Fe$_{1-x}$Cu$_x$)$_2$As$_2$.

cond-mat.supr-con↗

arXiv2013

Interlayer magnetic frustration driven quantum spin disorder in honeycomb compound In$_{3}$Cu$_{2}$VO$_{9}$

We present electronic and magnetic properties of a honeycomb compound In$_{3}$Cu$_{2}$VO$_{9}$ in this paper. We find that the parent phase is a charge transfer insulator with an energy gap of about 1.5 eV. Singly occupied d$_{3z^{2}-r^{2}}$ electrons of copper ions contribute an $S$ = 1/2 spin, while vanadium ions show nonmagnetism. Oxygen 2$p$ orbitals hybridizing with a small fraction of Cu 3$d$ orbitals dominate the density of states near $E_{F}$. The planar nearest-neighbor, next-nearest-neighbor and interplane superexchange couplings of Cu spins are $J_{1}$ $\approx$ 16.2 meV, $J_{2}$ $\approx$ 0.3 meV and $J_{z}$ $\approx$ 1.2 meV, suggesting a low-dimensional antiferromagnet \cite{Sondhi10}. We propose that the magnetic frustration along the c-axis leads to a quantum spin disorder in In$_{3}$Cu$_{2}$VO$_{9}$, in accordance with the recent experiments. {abstract}

cond-mat.supr-con↗