arXiv subjects

Danhong Huang

Publications and source records attributed to Danhong Huang.

At least 19 recordsLinked to original sources

arXiv2026

Suppressed plasmon excitations, enhanced damping and static screening in Kek-Y strained $α-\mathcal{T}_3$ model

We performed a rigorous theoretical and numerical investigation into the polarization function, plasmon excitations, and plasmon damping in the Kek-$α$ model, a two-dimensional material combining the key features of the $α-\mathcal{T}_3$ lattice and Kekule-distorted graphene. Unlike conventional Kek-Y graphene, the Kekule modulation in the Kek-$α$ model affects only one of the two sublattices, giving rise to a fundamentally new model with unusual electronic properties. The low-energy spectrum consists of two degenerate flat bands and two inequivalent Dirac cones with different Fermi velocities, referred to as the fast and slow cones. The particle-hole continuum responsible for Landau damping exhibits two distinct branches associated with transitions involving these Dirac cones. An additional particle-hole mode originates from electron transitions associated with the fast Dirac cone, appearing above the main diagonal. As the parameter $α$ increases, the contribution from the fast Dirac cone becomes dominant. The additional transitions involving the flat bands and the fast Dirac cone substantially reduce the region where undamped plasmons can exist, similarly to the conventional $α-\mathcal{T}_3$. Consequently, stable plasmons are observed only for relatively small values of $α$ or at very small wave vectors. These unusual electronic and collective properties make the Kek-$α$ model a promising platform for future plasmonic and nanoscale electronic applications.

cond-mat.mes-hall↗

arXiv2026

Surface Response, Plasma Modes of coated Multi-Layered anisotropic Semi-Dirac Heterostructures

We derived closed-form analytical expressions for the surface response functions (SRFs) for heterostructure. We investigate structures consisting of up to three layered, coated heterostructure of two-dimensional (2D) materials with a dielectric medium or vacuum interface. The dielectric media serves to inhibit charge transfer between layers for the case when a pair of 2D layers serve as coatings for a dielectric film. Our results revise the established picture for the dispersion equation for two layers of reduced dimensionality surrounded by dielectric media. An impinging electromagnetic field incident on the surface leads to Coulomb coupled plasma excitations in the structure which are yielded by the SRF. This is achieved by employing Maxwell's equations and linear response theory. We use these results to investigate the plasmonic properties of tilted semi-Dirac materials both analytically and numerically. Closed-form analytical expressions are derived for the plasmon dispersions in the long wavelength limit for single and double layers. We numerically obtain density plots of the loss functions and observe anisotropic behavior in different momentum directions. For the cases when there are two or three layers, we observe two plasmon branches corresponding to in-phase and out-of-phase charge density oscillations, where the in-phase optical modes have higher intensity than the out-of-phase acoustic modes. We calculated the optical absorption spectra for plasma modes in layered semi-Dirac materials produced by an external electromagnetic field carrying an electric polarization and frequency. Possible applications include durable protection coatings providing UV resistance, chemical protection and improving upon traditional ceramic coatings.

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arXiv2026

Exploring stable long-lifetime plasmon excitations in the Lieb lattice

The subject of the present paper is a thorough numerical investigation of plasmon expectations, their dispersions and damping within a Lieb lattice. The Lieb lattice is known for its unique low-energy band structure which consists of a bandgap as well as a flat band intersecting the conduction band at its lowest point. In contrast to previously studied dice lattice, the location of the current flat band exhibits reduced and broken symmetries, which give rise to interesting electronic and optical properties of this new material. In this work, we have investigated the conditions for observing a well-defined and stable plasmon mode within a wide frequency range. Specifically, we have considered a free-standing layer with various doping levels, as well as different types of monolayers of the Lieb lattice interacting with a surface-plasmon mode localized on top of a semi-infinite conductor. In particular, we have observed and described fully long-living plasmon modes with unusual energy dispersions. Additionally, we have carried out a detailed investigation on the static screening associated with the Lieb lattice. Our study has further revealed that these predicted features seem to be quite different from those of pseudospin-1 materials but resemble those of graphene instead.

cond-mat.mtrl-sci↗

arXiv2024

Polarizability and plasmons in pseudospin-1 gapped materials with a flat band

The collective electronic properties of various types of pseudospin-$1$ Dirac-cone materials with a flat band and finite bangaps in their energy spectra are the subject of our reported investigation. Specifically, we have calculated the dynamical polarization, plasmon dispersions as well as their decay rates due to Landau damping. Additionally, we present closed-form analytical expressions for the wave function overlaps for both the gapped dice lattice and the Lieb lattice. The gapped dice lattice is a special case of the more general $α$-${\cal T}_3$ model since its band structure is symmetric and the flat band remains dispersionless. On the other hand, the Lieb lattice has a flat band which appears at the lowest point of its conduction band. Our results for these two cases exhibit unique features in the plasmon spectra and their damping regions, which have never been reported in previous studies. For example, the particle-hole modes of a Lieb lattice appear as finite-size regions, while the plasmon modes exist only in a region with small wave numbers but an extended range of frequencies.

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arXiv2024

Self-consistent quantum-kinetic theory for interacting drifting electrons and force-driven phonons in a 1D system

A self-consistent quantum-kinetic model is developed for studying strong-field nonlinear electron transport interacting with force-driven phonons within a quantum-wire system. For this model, phonons can be dragged into motion through strong electron-phonon scattering by fast-moving electrons along the opposite direction of the DC electric field. Meanwhile, the DC-field induced charge current of electrons can be either enhanced or reduced by the same electron-phonon scattering, depending on the relative direction of a DC field with respect to that of an applied temperature gradient for driving phonons. By making use of this quantum-kinetic model beyond the relaxation-time approximation, neither electron nor phonon temperature is required for describing ultrafast electron-phonon scattering and their correlated transports in this 1D electronic-lattice system. onsistent quantum-kinetic model is developed for studying strong-field nonlinear electron transport interacting with force-driven phonons within a quantum-wire system. For this model, phonons can be dragged into motion through strong electron-phonon scattering by fast-moving electrons along the opposite direction of the DC electric field. Meanwhile, the DC-field induced charge current of electrons can be either enhanced or reduced by the same electron-phonon scattering, depending on the relative direction of a DC field with respect to that of an applied temperature gradient for driving phonons. By making use of this quantum-kinetic model beyond the relaxation-time approximation, neither electron nor phonon temperature is required for describing ultrafast electron-phonon scattering and their correlated transports in this 1D electronic-lattice system.

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arXiv2023

Dynamical polarization function, plasmons, their damping and collective effects in semi-Dirac bands

We have calculated the dynamical polarization, plasmons and damping rates in semi-Dirac bands (SDB's) with zero band gap and half-linear, half-parabolic low-energy spectrum. The obtained plasmon dispersions are strongly anisotropic and demonstrate some crucial features of both two-dimensional electron gas and graphene. Such gapless energy dispersions lead to a localized area of undamped and low-damped plasmons in a limited range of the frequencies and wave vectors. The calculated plasmon branches demonstrate an increase of their energies for a finite tilting of the band structure and a fixed Fermi level which could be used as a signature of a specific tilted spectrum in a semi-Dirac band.

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arXiv2023

Quantized Hall current in topological nodal-line semimetal

Photocurrent acts as one of measurable responses of material to light, which has proved itself to be crucial for sensing and energy harvesting. Topological semimetals with gapless energy dispersion and abundant topological surface and bulk states exhibit exotic photocurrent responses, such as novel quantized circular photogalvanic effect observed in Weyl semimetals. Here we find that for a topological nodal-line semimetal (NLSM) with nodal ring bulk states and drumhead surface states (DSS), a significant photocurrent can be produced by an electromagnetic (EM) wave by means of the quantum Hall effect. The Hall current is enabled by electron transfer between Landau levels (LLs) and triggered by both the electric field and magnetic field components of an EM wave. This Hall current is physically connected to an unusually large quantum-Hall conductivity of the zeroth LLs resulting from quantized DSS. These LLs are found to be highly degenerate due to the unique band-folding effect associated with magnetic-field-induced expansion of a unit cell. Furthermore, we observe that the Hall current induced solely by an in-plane linearly-polarized EM wave becomes a quantized entity which allows for possible direct measurement of the DSS density in a topological NLSM. This work paves a way toward designing high-magnetic-field-sensitivity detection devices for industrial and space applications, such as the development of self-detection of current-surge-induced overheating in electronic devices and accurate Earth's magnetic-anomaly maps for guiding a self-navigating drone or an aircraft.

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arXiv2022

Dynamical optical conductivity for gapped $α-\mathcal{T}_3$ materials with a curved "flat" band

We have calculated the dynamical optical conductivity for $α-\mathcal{T}_3$ materials in the presence of a finite bandgap in their energy bandstructure. This is a special type of energy dispersions because for all $α-\mathcal{T}_3$ materials with a bandgap, except graphene and a dice lattice limits, the flat band receives a non-zero dispersion and assumes a curved shape. The infinite ${\bf k}$-degeneracy of the flat energy band is also lifted. Such a low-energy bandstructure could be obtained if an $α-\mathcal{T}_3$ material is irradiated off-resonant with circularly polarized light. We have calculated the optical conductivity for the zero and finite temperatures, as well as for the cases of a finite and nearly-zero doping. We have demonstrated that analytical expressions could be in principle obtained for all types of gapped $α-\mathcal{T}_3$ materials and provided the closed-form analytical expressions for a gapped dice lattice. Our numerical results reveal some well-known signatures of the optical conductivity in $α-\mathcal{T}_3$ and silicene with two non-equivalent bandgaps, as well as demonstrate some very specific features which have not been previously found in any existing Dirac materials.

cond-mat.mtrl-sci↗

arXiv2022

Floquet engineering of titled and gapped Dirac materials

We have established a rigorous theoretical formalism for Floquet engineering, or investigating and eventually tailoring most crucial electronic properties of tetragonal molybdenum disulfide (1T$^\prime$-MoS$_2$), by applying an external high-frequency dressing field in the off-resonant regime. It was recently demonstrated that monolayer semiconducting1T$^\prime$-MoS$_2$ may assume a distorted tetragonal structure which exhibits tunable and gapped spin- and valley-polarized tilted Dirac bandstructure. From the viewpoint of electronics, 1T$^\prime$-MoS$_2$ is one of the most technologically promising nanomaterials and a novel representative of an already famous family of transition metal dichalcogenides. The obtained dressed states strongly depend on the polarization of the applied irradiation and reflect the full complexity of the initial low-energy Hamiltonian of non-irradiated material. We have calculated and analyzed the obtained electron dressed states for linear and circular types of the polarization of the applied field focusing on their symmetrical properties, anisotropy, tilting and bandgaps, as well as topological signatures. Since a circularly polarized dressing field is also known to induce a transition into a new state with broken time-reversal symmetry and a non-zero Chern number, the combination of these topologically non-trivial phases and transitions between them could reveal some truly unique and earlier unknown phenomena.

cond-mat.mtrl-sci↗

arXiv2022

Developing a semiclassical Wentzel-Kramers-Brillouin theory for $α-\mathcal{T}_3$ model

We have developed a complete semiclassical Wentzel-Kramers-Brillouin (WKB) theory for $α-\mathcal{T}_3$ model which describes a wide class of existing pseudospin-1 Dirac cone materials. By expanding the sought wave functions in a series over the powers of Planck constant $\hbar$, we have obtained the leading order expansion term which is the key quantity required for calculating the electronic and transport properties of a semiclassical electron in $α-\mathcal{T}_3$. We have derived the transport equations connecting each two consecutive orders of the wave function expansion and solved them to obtained the first order WKB wavefunction. We have also discussed the applicability of the obtained approximation and how these results could be used to investigate various tunneling and transport properties of $α-\mathcal{T}_3$ materials with non-trivial potential profiles. Our results could be also helpful for constructing electronics devices and transistors based on innovative flat-band Dirac materials.

cond-mat.mes-hall↗

arXiv2022

Rashba spin-orbit coupling and quantum-interference effect for a pair of spin-correlated electrons in their tunneling and reflection under a step potential

We present both theory and numerical-computation results for the transmission and reflection probability currents of a charged particle across a potential step in the presence of a Rashba spin-orbit interaction. By varying kinetic energy and angle of incident electrons or barrier height, different features associated with tunneling and reflection of electrons are revealed by inter-spin-channel electron tunnelings and reflections. These unique properties are further accompanied by spin-state quantum interference of either a reflected or transmitted pairs of spin-correlated electrons with the same kinetic energy but in different spin-orbital states. Such distinctive features are expected to give rise to a lot of applications in both spintronics and quantum-computation devices.

cond-mat.mes-hall↗

arXiv2022

Finite-temperature plasmons, damping and collective behavior for $α-\mathcal{T}_3$ model

We have conducted a thorough theoretical and numerical investigation of the electronic susceptibility, polarizability, plasmons, their damping rates, as well as the static screening in pseudospin-1 Dirac cone materials with a flat band, or for a general $α- \mathcal{T}_3$ model, at finite temperatures. This includes calculating the polarization function, plasmon dispersions and their damping rates at arbitrary temperatures and obtaining analytical approximations the long wavelength limit, low and high temperatures. We demonstrate that the integral transformation of the polarization function cannot be used directly for a dice lattice revealing some fundamental properties and important applicability limits of the flat band dispersions model. At $k_B T \ll E_F$, the largest temperature-induced change of the polarization function and plasmons comes from the mismatch between the chemical potential and the Fermi energy. We have also obtained a series of closed-form semi-analytical expressions for the static limit of the polarization function of an arbitrary $α- \mathcal{T}_3$ material at any temperature with exact analytical formulas for the high, low and zero temperature limits which is of tremendous importance for all types of transport and screening calculations for the flat band Dirac materials.

cond-mat.mtrl-sci↗

arXiv2022

Generalized Peierls substitution for the tight-binding model of twisted multilayer graphene in a magnetic field

We propose a generalized Peierls substitution method in conjunction with the tight-binding model to explore the magnetic quantization and quantum Hall effect in twisted multilayer graphene under a magnetic field. The Bloch-basis tight-binding Hamiltonian is constructed for large twist angle while a simplified tight-binding model is employed for the magic angle. We investigate extensively the band structures, Landau levels (LLs), and quantum Hall conductivity (QHC) of twisted bilayer graphene and twisted double bilayer graphene, as well as their dependence on the twist angle. Comparison between these crucial properties of monolayer graphene, Bernal bilayer graphene, and the twisted systems is carefully made to highlight the roles played by twisting. The unique selection rules of inter-LL transition, which is crucial for achieving a deep understanding of the step structures of QHC, are identified through the properties of LL wave functions. Our theoretical model opens up an opportunity for comprehension of the interplay between an applied magnetic field and the twisting effect associated with multilayer graphene.

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arXiv2021

Tunneling conductivity fast modulated by optically-dressed electrons in graphene and a dice lattice

Based on the transmission coefficient of tunneling electrons, we have presented tunneling current and conductivity across a square-potential barrier for both graphene and $α$-$\mathcal{T}_3$ lattices under a linearly-polarized off-resonant dressing field. The presence of such a dressing field introduces an anisotropy factor in the energy dispersion of tunneling electrons so that the cross section of a Dirac-cone appears as elliptical. Consequently, the field-polarization controlled major axis of the ellipse will be misaligned with the normal direction of a barrier layer in the tunneling system, which exhibits an asymmetric Klein-paradox for an off-normal-direction tunneling. The resulting tunneling current in this system is calculated by using a transmission coefficient and a longitudinal group velocity (different from a longitudinal momentum) of electrons. By presenting numerically calculated tunneling conductivity modified by a laser dressing field, we demonstrate a significant enhancement of electrical conductivity by external laser-field intensity, which is expected to be crucial in application of ultrafast optical modulation of opto-electronic devices for photo-detection and fiber-optic communication.

cond-mat.mes-hall↗

arXiv2021

Engineering plasmon modes and their loss in armchair graphene nanoribbons by selected edge-extended defects

The effect of edge modification of armchair graphene nanoribbons (AGNRs) on the collective excitations are theoretically investigated. The tight-binding method is employed in conjunction with the dielectric function. Unconventional plasmon modes and their association with the flat bands of the specially designed AGNRs are thoroughly studied. We demonstrate the robust relationship between the novel collective excitations and both the type and period of the edge modification. Additionally, we reveal that the main features displayed in the (momentum, frequency)-phase diagrams for both single-particle and collective excitations of AGNRs can be efficiently tuned by edge-extended defects. Our obtained plasmon modes are found to be analogous to magnetoplasmons associated with collective excitations of Landau-quantized electrons. This work provides a unique way to engineer discrete magnetoplasmon-like modes of AGNRs in the absence of magnetic field.

cond-mat.mes-hall↗

arXiv2021

Adjustable propagating plasmons in $α-\mathcal{T}_3$ lattice-based armchair nanoribbons

We have obtained and analyzed the electronic states, polarization function and the plasmon excitations for $α- \mathcal{T}_3$-based nanoribbons with armchair termination. The calculated plasmon dispersions strongly depend on the number of the atomic rows across the ribbon, and the presence of the energy gap between the valence and conduction bands which is also determined by the nanoribbon geometry. The bandgap was proven to have the strongest effect on both the plasmon dispersions and their Landau damping. We have also demonstrated that for a small electron doping the plasmon dispersions do not depend on the relative hopping parameter $α$ of the considered $α- \mathcal{T}_3$ material in the long-wave limit and investigated the conditions when $α$ becomes an important factor which strongly affects the plasmons. We believe that our new uncovered electronic and collective properties of nano-size $α- \mathcal{T}_3$ribbons will find their applications in the field of modern electronics and nanodevices.

cond-mat.mes-hall↗

arXiv2021

Coherent-scatterer enhancement and Klein-tunneling suppression by potential barriers in gapped graphene with chirality-time-reversal symmetry

We have utilized the finite-difference approach to explore electron-tunneling properties in gapped graphene through various electrostatic-potential barriers changing from Gaussian to a triangular envelope function in comparison with a square potential barrier. Transmission coefficient is calculated numerically for each case and applied to corresponding tunneling conductance. It is well known that Klein tunneling in graphene will be greatly reduced in a gapped graphene. Our results further demonstrate that such a decrease of transmission can be significantly enhanced for spatially-modulated potential barriers. Moreover, we investigate the effect from a bias field applied to those barrier profiles, from which we show that it enables the control of electron flow under normal incidence. Meanwhile, the suppression of Klein tunneling is found more severe for a non-square barrier and exhibits a strong dependence on bias-field polarity for all kinds of barriers. Finally, roles of a point impurity on electron transmission and conductance are analyzed with a sharp peak appearing in electron conductance as the impurity atom is placed at the middle of a square barrier. For narrow triangular and Gaussian barriers, however, the conductance peaks become significantly broadened, associated with an enhancement in tunneling conductance.

cond-mat.mes-hall↗

arXiv2021

Defect capturing and charging dynamics and their effects on magneto-transport of electrons in quantum wells

The defect corrections to polarization and dielectric functions of Bloch electrons in quantum wells are first calculated. Following this, we derive the first two moment equations from Boltzmann transport theory and apply them to explore defect effects on magneto-transport of Bloch electrons. Meanwhile, we obtain analytically the momentum-relaxation time and mobility tensor for Bloch electrons making use of the screened defect-corrected polarization function. Based on quantum-statistical theory, we further investigate the defect capture and charging dynamics by employing a parameterized physics model for defects to obtain defect wave functions. After this, both capture and relaxation rates, as well as density for captured Bloch electrons, are calculated self-consistently as functions of temperature, doping density and different defect types. By applying the energy-balance equation, the number of occupied energy levels and chemical potential of defects are determined, with which the transition rate for defect capturing is obtained. By using these results, defect energy-relaxation, capture and escape rates, and Bloch-electron chemical potential are obtained self-consistently. At the same time, the Bloch-electron energy- and momentum-relaxation rates, as well as the current suppression factor, are also investigated quantitatively. Finally, by combining all these studies together, the temperature dependence of the Hall and longitudinal mobilities is demonstrated for Bloch electrons in either single- or multi-quantum wells, which can be utilized for quantifying burst noise in transistors and blinking noise in photo-detectors.

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