Searcharxiv⌕ Search

arXiv subjects

Weiliang Wang

Publications and source records attributed to Weiliang Wang.

At least 19 recordsLinked to original sources
arXiv2025

Generalized Huang's Equation for Phonon Polariton in Polyatomic Polar Crystal

The original theory of phonon polariton is Huang's equation which is suitable for diatomic polar crystals only. We proposed a generalized Huang's equation without fitting parameters for phonon polariton in polyatomic polar crystals. We obtained the dispersions of phonon polariton in GaP (bulk), hBN (bulk and 2D), α-MoO3 (bulk and 2D) and ZnTeMoO6 (2D), which agree with the experimental results in the literature and of ourselves. We also obtained the eigenstates of the phonon polariton. We found that the circular polarization of the ion vibration component of these eigenstates is nonzero in hBN flakes. The result is different from that of the phonon in hBN.

cond-mat.mtrl-sci↗
arXiv2024

Hyperbolic phonon polaritons and wave vector direction dependent dielectric tensors in anisotropic crystals

Hyperbolic phonon polariton is important in precisely controlling photons at the nanoscale. It was common practice to calculate the dielectric function of the phonon polariton system with the Drude-Lorenz model. We considered the impact of LO-TO splitting while applying the Drude-Lorenz model. Then the dielectric functions become wave vector direction dependent besides electric polarization direction dependent. Our results show that considering LO-TO splitting can more accurately predict dielectric functions. Additionally, we discovered that, besides hexagonal BN, hexagonal AlN exhibits a wide hyperbolic frequency band range, while the other four materials display it scarcely. Furthermore, we found that the phonon frequency, lifetime, and the difference of infrared active transverse optical phonon frequencies with different wave vector directions are critical factors in determining the width of the hyperbolic frequency band range. We also found some dumbbell-shaped and butterfly-shaped isofrequency curves in h-AlN, h-GaP, and especially h-GaN. Our study provides a fresh perspective on understanding the dielectric properties of these materials and lays a theoretical foundation for further exploration and development of new hyperbolic phonon polariton materials.

cond-mat.mtrl-sci↗
arXiv2024

Phonon pseudoangular momentum in $α$-MoO$_3$

In recent studies, it has been discovered that phonons can carry angular momentum, leading to a series of investigations into systems with 3-fold rotation symmetry. However, for systems with 2-fold screw rotational symmetry, such as $α$-MoO$_3$, there has been no relevant discussion. In this paper, we investigated the pseudoangular momentum of phonons in crystals with 2-fold screw rotational symmetry. Taking $α$-MoO$_3$ as an example, we explain the selection rules in circularly polarized Raman experiments resulting from pseudoangular momentum conservation, providing important guidance for experiments. This study of pseudoangular momentum in $α$-MoO$_3$ opens up a new degree of freedom for its potential applications, expanding into new application domains.

cond-mat.mtrl-sci↗
arXiv2023

Coexistence of zigzag antiferromagnetic order and superconductivity in compressed NiPSe3

NiPSe3 is regarded as a bandwidth-controlled Mott insulator, distinct from the widely studied Mott insulating magnetic graphene MPSe3 (M = Mn and Fe) family. By employing high-pressure synchrotron X-ray diffraction, we observe two structural transitions as a function of pressure. With the help of first-principles calculations, we discover the antiferromagnetic (AFM) moment directions of NiPSe3 switch from out-of-plane to in-plane and the honeycomb layers slide relative to each other at the first structural transition. The in-plane AFM order persists until the second structural transition, whereupon the two-dimensional (2D) structure assumes a more three-dimensional (3D) character. A bandwidth-controlled Mott insulator-metal transition (IMT) occurs between the two structural transitions at 8.0 GPa, concomitant with the emergence of superconductivity with 4.8 K. The superconductivity in NiPSe3 emerging in the 2D monoclinic phase coexists with the in-plane AFM order and continues into the 3D trigonal phase. Our electronic structure calculations reveal that the Mott IMT and superconductivity in NiPSe3 are both closely related to the enhanced Se2- 4p and Ni2+ 3d electronic hybridizations under pressure. From these results, we construct the temperature-pressure electronic phase diagram of NiPSe3, revealing rich physics and many similarities with copper oxide and iron-based superconductors.

cond-mat.supr-con↗
arXiv2022

Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe2

We report high pressure studies on the C-type antiferromagnetic semiconductor EuTe2 up to 36.0 GPa. A structural transition from the I4/mcm to C2/m space group is identified at ~16 GPa. Superconductivity is discovered above ~5 GPa in both the I4/mcm and C2/m space groups. In the low-pressure phase (< 16 GPa), the antiferromagnetic transition temperature is enhanced with increasing pressure due to the enhanced magnetic exchange interactions. Magnetoresistance measurements indicate an interplay between the local moments of Eu2+ and the conduction electrons of Te 5p orbits. The upper critical field of the superconductivity is well above the Pauli limit. Across the structural transition to the high-pressure phase (> 16 GPa), EuTe2 becomes nonmagnetic and the superconducting transition temperature evolves smoothly with the upper critical field below the Pauli limit. Therefore, the high upper critical field of EuTe2 in the low-pressure phase is due to the exchange field compensation effect of the Eu magnetic order and the superconductivity in both structures may arise in the framework of the BCS theory.

cond-mat.supr-con↗
arXiv2022

Higher dimensional shrinking target problem in beta dynamical systems

We consider the two dimensional shrinking target problem in the beta dynamical system for general $β>1$ and with the general error of approximations. Let $f, g$ be two positive continuous functions. For any $x_0,y_0\in[0,1]$, define the shrinking target set $$ E(T_β, f,g):=\left\{(x,y)\in [0,1]^2: \begin{array}{ll} |T_β^{n}x-x_{0}|<e^{-S_nf(x)}\\ [1ex] |T_β^{n}y-y_{0}|< e^{-S_ng(y)} \end{array} \ {\text{for infinitely many}} \ n\in \N \right\}, $$ where $S_nf(x)=\sum_{j=0}^{n-1}f(T_β^jx)$ is the Birkhoff sum. We calculate the Hausdorff dimension of this set and prove that it is the solution to some pressure function. This represents the first result of this kind for the higher dimensional beta dynamical systems.

math.NT↗
arXiv2017

Electronic Structure and Band Gap Engineering of Two-Dimensional Octagon-Nitrogene

We have predicted a new phase of nitrogen with octagon structure in our previous study, which we referred to as octa-nitrogene (ON). In this work, we make further investigation on its electronic structure. The phonon band structure has no imaginary phonon modes, which indicates that ON is dynamically stable. Using ab initio molecular dynamic simulations, the structure is found to stable up to 100K, and ripples that are similar to that of graphene is formed on the ON sheet. Based on DFT calculation on its band structure, single layer ON is a 2D large-gap semiconductor with a band gap of 4.7eV. Because of inter-layer interaction, stackings can decrease the band gap. Biaxial tensile strain and perpendicular electric field can greatly influence the band structure of ON, in which the gap decreases and eventually closes as the biaxial tensile strain or the perpendicular electric field increases. In other words, both biaxial tensile strain and perpendicular electric field can drive the insulator-to-metal transition, and thus can be used to engineer the band gap of ON. From our results, ON has potential applications in the electronics, semiconductors, optics and spintronics, and so on.

cond-mat.mtrl-sci↗
arXiv2017

Room-temperature vacuum Rabi splitting with active control in two-dimensional atomic crystals

Strong light-matter coupling manifested by vacuum Rabi splitting has attracted tremendous attention due to its fundamental importance in cavity quantum-electrodynamics research and great potentials in quantum information applications. A prerequisite for practical applications of the strong coupling in future quantum information processing and coherent manipulation is an all-solid-state system exhibiting room-temperature vacuum Rabi splitting with active control. Here we realized such a system in heterostructure consisting of monolayer WS2 and an individual plasmonic gold nanorod. By taking advantage of both of the small mode volume of the nanorod and large binding energy of the WS2 exciton, giant vacuum Rabi splitting energies of 91 meV ~ 133 meV can be obtained at ambient conditions, which only involve 5 ~ 18 excitons. The vacuum Rabi splitting can be dynamically tuned either by electrostatic gating or temperature scanning. These findings could pave the way towards active quantum optic devices operating at room temperature.

physics.optics↗
arXiv2014

Field Evaporation of Grounded Arsenic Doped Silicon Clusters

We have investigated field evaporation of grounded arsenic (As) doped silicon (Si) clusters consist of 52 atoms with density functional theory to mimic Si nano structures of hundreds of nanometers long standing on a substrate. Six cluster structures with different As doping concentrations and dopant locations are studied. The critical evaporation electric fields are found to be lower for clusters with higher doping concentrations and doping sites closer to the surface. We attribute the difference to the difference in binding energies corresponding to the different As-doping concentrations and to the doping locations. Our theoretical study could shed light on the stability of nano apexs under high electric field.

physics.comp-ph↗
arXiv2014

Disintegration of graphene nanoribbons in large electrostatic fields

The deformation and disintegration of a graphene nanoribbon under external electrostatic fields are investigated by first principle quantum mechanical calculations to establish its stability range. The zigzag edges terminated by various functional groups are considered. By analyzing the phonon spectrum, the critical fracture field for each edge structure is obtained. It is found that different terminal groups on the zigzag graphene nanoribbons lead to different fracture patterns at different fracture fields. The failure mechanism is demonstrated to rely on both the carbon bond alternation feature across the ribbon and terminal group electronegativity.

cond-mat.mes-hall↗
arXiv2012

Comment on slope of nonlinear FN plot and field enhancement factor

It is common practice to extract field enhancement factor from the slope of FN plot. Many experimentalists working on field electron emission had reported multi-(linear segment) FN plots, which can be divided into several (usually two) linear segments. Then multi-(field enhancement factor) were extracted from the FN plot. They claimed that the field enhancement factor increases with applied field if the FN plot bends downward (vice versus if the FN plot bends upward). We show that this is contrary to fact.

cond-mat.mtrl-sci↗
arXiv2012

Graphene with the secondary amine-terminated zigzag edge as a line electron emitter

An extraordinary low vacuum barrier height of 2.30 eV has been found on the zigzag-edge of graphene terminated with the secondary amine via the ab initio calculation. This edge structure has a flat band of edge states attached to the gamma point where the transversal kinetic energy is vanishing. We show that the field electron emission is dominated by the flat band. The edge states pin the Fermi level to a constant, leading to an extremely narrow emission energy width. The graphene with such edge is a promising line field electron emitter that can produce highly coherent emission current.

cond-mat.mtrl-sci↗
arXiv2011

The exchange-correlation potential correction to the vacuum potential barrier of graphene edge

We investigated the vacuum potential barriers of various graphene edges terminated with hydrogen, oxygen, hydroxyl group and ether group respectively. It is found that the exchange-correlation potential correction is significant to the edge structures with electronegativity higher than carbon. The correction leads to the local work function decreased by more than 1. eV for the O terminated edge, while the local work function of H and OH terminated edges remain unchanged.

cond-mat.mtrl-sci↗
arXiv2011

Analytic study on cold field electron emission from metallic nanowall array

The cold field electron emission from metallic nanowall array is investigated theoretically. Via conformal mapping method, analytic formulas of tunneling barrier, edge field enhancement factor, transmission coefficient, and area emission current density are derived in the semi-classical approximation. The influence of field enhancement effects and screening effects on cold field emission are discussed and the optimal spacing distance between nanowalls for the largest emission current density is found to be a linear function of the height of nanowalls and depends on the applied field.

cond-mat.mes-hall↗
arXiv2011

Potential barrier of Graphene edges

We calculated row resolved density of states, charge distribution and work function of graphene's zigzag and armchair edge (either clean or terminated alternatively with H, O or OH group). The zigzag edge saturated via OH group has the lowest work function of 3.76 eV, while the zigzag edge terminated via O has the highest work function of 7.74 eV. The angle-dependent potential barrier on the edge is fitted to a multi-pole model and is explained by the charge distribution.

cond-mat.mtrl-sci↗
arXiv2011

Field electron emission characteristic of graphene

The field electron emission current from graphene is calculated analytically on a semiclassical model. The unique electronic energy band structure of graphene and the field penetration in the edge from which the electrons emit have been taken into account. The relation between the effective vacuum barrier height and the applied field is obtained. The calculated slope of the Fowler-Nordheim plot of the current-field characteristic is in consistent with existing experiments.

cond-mat.mtrl-sci↗
arXiv2010

Analytical treatment of cold field electron emission from a nanowall emitter

This paper presents an elementary, approximate analytical treatment of cold field electron emission (CFE) from a classical nanowall. A simple model is used to bring out some of the basic physics of a class of field emitter where quantum confinement effects exist transverse to the emitting direction. A high-level methodology is presented for developing CFE equations more general than the usual Fowler-Nordheim-type (FN-type) equations, and is applied to the classical nanowall. If the nanowall is sufficiently thin, then significant transverse-energy quantization effects occur, and affect the overall form of theoretical CFE equations; also, the tunnelling barrier shape exhibits "fall-off" in the local field value with distance from the surface. A conformal transformation technique is used to derive an analytical expression for the on-axis tunnelling probability.

cond-mat.mes-hall↗