arXiv subjects

Ming-Fa Lin

Publications and source records attributed to Ming-Fa Lin.

At least 73 records · Page 4Linked to original sources

arXiv2015

Feature-rich electronic excitations in external fields of 2D silicene

Electronic Coulomb excitations in monolayer silicene are investigated by using the Lindhard dielectric function and a newly developed generalized tight-binding model (G-TBM). G-TBM simultaneously contains the atomic interactions, the spin-orbit coupling, the Coulomb interactions, and the various external fields at an arbitrary chemical potential. We exhibit the calculation results of the electrically tunable magnetoplasmons and the strong magnetic field modulation of plasmon behaviors. The two intriguing phenomena are well explained by determining the dominant transition channels in the dielectric function and through understanding the electron behavior under the multiple interactions (intrinsic and external). A further tunability of the plasmon features is demonstrated with the momentum transfer and the Fermi energy. The methodological strategy could be extended to several other 2D materials like germanene and stanene, and might open a pathway to search a better system in nanoplasmonic applications.

cond-mat.mes-hall↗

arXiv2015

Rich magneto-absorption spectra in AAB-stacked trilayer graphene

The generalized tight-binding model is developed to investigate the feature-rich magneto-optical properties of AAB-stacked trilayer graphene. Three intragroup and six intergroup inter-Landau-level (inter-LL) optical excitations largely enrich the magneto-absorption peaks. In general, the former are much higher than the latter, depending on the phases and amplitudes of LL wavefunctions. The absorption spectra exhibit the single- or twin-peak structures which are determined by the quantum modes, LL energy spectra and Fermion distribution. The splitting LLs, with different localization centers (2/6 and 4/6 positions in a unit cell), can generate very distinct absorption spectra. There exist extra single peaks because of LL anticrosings. AAB, AAA, ABA, and ABC stackings quite differ from one another in terms of the inter-LL category, frequency, intensity, and structure of absorption peaks. The main characteristics of LL wavefunctions and energy spectra and the Fermi-Dirac function are responsible for the configuration-enriched magneto-optical spectra.

physics.comp-ph↗

arXiv2015

Geometric, magnetic and electronic properties of folded graphene nanoribbons

Geometric and electronic properties of folded graphene nanoribbons (FGNRs) are investigated by first-principles calculations. These properties are mainly dominated by the competition or cooperation among stacking, curvature and edge effects. For the zigzag FGNRs, the more stable structures are revealed to be AB stackings, while for the armchair types, AA" stackings are more stable. The interlayer interactions and hybridization of four orbitals lead to smaller energy gaps, anti-crossing bands, and more band-edge states. Specifically, the broken mirror symmetry in the odd-AB stacked zigzag FGNRs is responsible for the spin-up and spin-down splitting subbands. All FGNRs are direct-gap semiconductors except that the edge-edge interactions cause the even-AA stacked zigzag FGNRs to exhibit a pair of metallic linear bands. The width-dependent energy gaps in the armchair FGNRs can be classified into six groups. Furthermore, there exist rich features in density of states, including the form, number, intensity and energy of the special structures.

physics.comp-ph↗

arXiv2015

Chemical Bondings Induced Rich Electronic Properties of Oxygen Absorbed Few-layer Graphenes

Electronic properties of graphene oxides enriched by the strong chemical bondings are investigated using first-principle calculations. They are very sensitive to the changes in the number of graphene layer, stacking configuration, and distribution of oxygen. The feature-rich electronic structures exhibit the destruction or distortion of Dirac cone, opening of band gap, anisotropic energy dispersions, O- and (C,O)-dominated energy dispersions, and extra critical points. All the few-layer graphene oxides are semi-metals except for the semiconducting monolayer ones. For the former, the distorted Dirac-cone structures and the O-dominated energy bands near the Fermi level are revealed simultaneously. The orbital-projected density of states (DOS) have many special structures mainly coming from a composite energy band, the parabolic and partially flat ones. The DOS and spatial charge distributions clearly indicate the critical bondings in O-O, C-O and C-C bonds, being responsible for the diversified properties.

cond-mat.mtrl-sci↗

arXiv2015

Magnetic quantization in multilayer graphenes

Essential properties of multilayer graphenes are diversified by the number of layers and the stacking configurations. For an $N$-layer system, Landau levels are divided into $N$ groups, with each identified by a dominant sublattice associated with the stacking configuration. We focus on the main characteristics of Landau levels, including the degeneracy, wave functions, quantum numbers, onset energies, field-dependent energy spectra, semiconductor-metal transitions, and crossing patterns, which are reflected in the magneto-optical spectroscopy, scanning tunneling spectroscopy, and quantum transport experiments. The Landau levels in AA-stacked graphene are responsible for multiple Dirac cones, while in AB-stacked graphene the Dirac properties depend on the number of graphene layers, and in ABC-stacked graphene the low-lying levels are related to surface states. The Landau-level mixing leads to anticrossings patterns in energy spectra, which are seen for intergroup Landau levels in AB-stacked graphene, while in particular, a formation of both intergroup and intragroup anticrossings is observed in ABC-stacked graphene. The aforementioned magneto-electronic properties lead to diverse optical spectra, plasma spectra, and transport properties when the stacking order and the number of layers are varied. The calculations are in agreement with optical and transport experiments, and novel features that have not yet been verified experimentally are presented.

physics.comp-ph↗

arXiv2015

The effect of perpendicular electric field on Temperature-induced plasmon excitations for intrinsic silicene

We use the tight-binding model and the random-phase approximation to investigate the intrinsic plasmon in silicene. At finite temperatures, an undamped plasmon is generated from the interplay between the intraband and the interband-gap transitions. The extent of the plasmon existence range in terms of momentum and temperature, which is dependent on the size of single-particle-excitation gap, is further tuned by applying a perpendicular electric field. The plasmon becomes damped in the interband-excitation region. A low damped zone is created by the field-induced spin split. The field-dependent plasmon spectrum shows a strong tunability in plasmon intensity and spectral bandwidth. This could make silicene a very suitable candidate for plasmonic applications.

cond-mat.mtrl-sci↗

arXiv2015

H-Si bonding-induced unusual electronic properties of silicene: a method to identify hydrogen concentration

Hydrogenated silicenes possess peculiar properties owing to the strong H-Si bonds, as revealed by an investigation using first principles calculations. The various charge distributions, bond lengths, energy bands, and densities of states strongly depend on different hydrogen configurations and concentrations. The competition of strong H-Si bondings and weak sp3 hybridization dominate the electronic properties. Chair configurations belong to semiconductors, while the top configurations show a nearly dispersionless energy band at the Fermi level. Both two systems display H-related partially flat bands at middle energy, and recovery of low-lying πbands during the reduction of concentration. Their densities of states exhibit prominent peaks at middle energy, and the top systems have a delta-funtion-like peak at E=0. The intensity of these peaks are gradually weakened as the concentration decreases, providing an effective method to identify the H-concentration in scanning tunneling spectroscopy experiments.

cond-mat.mtrl-sci↗

arXiv2015

Configuration-enriched magnetoelectronic spectra of AAB-stacked trilayer graphene

We developed the generalized tight-binding model to study the magneto-electronic properties of AAB-stacked trilayer graphene. Three groups of Landau levels (LLs) are characterized by the dominating subenvelope function on distinct sublattices. Each LL group could be further divided into two sub-groups in which the wavefunctions are, respectively, localized at 2/6 (5/6) and 4/6 (1/6) of the total length of the enlarged unit cell. The unoccupied conduction and the occupied valence LLs in each sub-group behave similarly. For the first group, there exist certain important differences between the two sub-groups, including the LL energy spacings, quantum numbers, spatial distributions of the LL wavefunctions, and the field-dependent energy spectra. The LL crossings and anticrossings occur frequently in each sub-group during the variation of field strengths, which thus leads to the very complex energy spectra and the seriously distorted wavefunctions. Also, the density of states (DOS) exhibits rich symmetric peak structures. The predicted results could be directly examined by experimental measurements. The magnetic quantization is quite different among the AAB-, AAA-, ABA-, and ABC-stacked configurations.

cond-mat.mtrl-sci↗

arXiv2014

Feature-Rich Electronic Properties in Graphene Ripples

Graphene ripples possess peculiar essential properties owing to the strong chemical bonds, as an investigation using first principle calculations clearly revealed. Various charge distributions, bond lengths, energy bands, and densities of states strongly depend on the corrugation structures, ripple curvatures and periods. Armchair ripples belonging to a zero-gap semiconductor display split middle-energy states, while the zigzag ripples exhibit highly anisotropic energy bands, semi-metallic behavior implicated by the destruction of the Dirac cone, and the newly created critical points. Their density of states exhibit many low-lying prominent peaks and can explain the experimental measurements. There exist certain important similarities and differences between graphene ripples and carbon nanotubes.

cond-mat.mtrl-sci↗

arXiv2014

Beating oscillations of magneto-optical spectra in simple hexagonal graphite

The magneto-optical properties of simple hexagonal graphite exhibit rich beating oscillations, which are dominated by the field strength and photon energy. The former has a strong effect on the intensity, the energy range of the beating and the number of groups, and the latter modulates the total group numbers of the oscillation structures. The single-particle and collective excitations are simultaneously presented in the magnetoreflectance spectra and can be precisely distinguished. For the loss function and reflectance, the beating pattern of the first group displays stronger intensities and broader energy range than other groups. Simple hexagonal graphite possesses unique magneto-optical characteristics that can serve to identify other bulk graphites.

cond-mat.mtrl-sci↗

arXiv2014

Feature-Rich Magnetic Quantization in Sliding Bilayer Graphenes

The generalized tight-binding model, based on the subenvelope functions of distinct sublattices, is developed to investigate the magnetic quantization in sliding bilayer graphenes. The relative shift of two graphene layers induces a dramatic transformation between the Dirac-cone structure and the parabolic band structure, and thus leads to drastic changes of Landau levels (LLs) in the spatial symmetry, initial formation energy, intergroup anti-crossing, state degeneracy and semiconductor-metal transition. There exist three kinds of LLs, i.e., well-behaved, perturbed and undefined LLs, which are characterized by a specific mode, a main mode plus side modes, and a disordered mode, respectively. Such LLs are clearly revealed in diverse magneto-optical selection rules. Specially, the undefined LLs frequently exhibit intergroup anti-crossings in the field-dependent energy spectra, and show a large number of absorption peaks without optical selection rules.

cond-mat.mtrl-sci↗

arXiv2014

Magneto-optical selection rules of curved graphene nanoribbons and carbon nanotubes

We derive the generalized magneto-absorption spectra for curved graphene nanorib- bons and carbon nanotubes by using the Peierls tight-binding model. The main spectral characteristics and the optical selection rules result from the cooperative or competitive relationships between the geometric structure and a magnetic field. In curved ribbons, the dominant selection rule remains unchanged during the variation of the curvature. When the arc angle increases, the prominent peaks are split, with some even vanishing as the angle exceeds a critical value. In carbon nanotubes, the angular-momentum coupling induces extra selection rules, of which more are revealed due to the increase of either (both) of the factors: tube diameter and field strength. Particularly once the two factors exceed certain critical values, the optical spectra could reflect the quasi-Landau-level structures. The identifying features of the spec- tra provide insight into optical excitations for curved systems with either open or closed boundary condition.

cond-mat.mtrl-sci↗

arXiv2014

Electrically tunable plasma excitations in AA-stacking multilayer graphene

We use a tight-binding model and the random-phase approximation to study the Coulomb excitations in simple-hexagonal-stacking multilayer graphene and discuss the field effects. The calculation results include the energy bands, the response functions, and the plasmon dispersions. A perpendicular electric field is predicted to induce significant charge transfer and thus capable of manipulating the energy, intensity, and the number of plasmon modes. This could be further validated by inelastic light scattering or electron-energy-loss spectroscopy.

cond-mat.mtrl-sci↗

arXiv2014

Combined Effect of Stacking and Magnetic Field on Plasmon Excitations in Bilayer Graphene

The electronic excitations of bilayer graphene (BLG) under a magnetic field are investigated with the use of the Peierls tight-binding model in conjunction with random-phase approximation (RPA). The interlayer atomic interactions, interlayer Coulomb interactions, and magnetic field effects are simultaneously included in the dielectric-function matrix. That enables us to derive the magneto-Coulomb-excitation spectrum of different stacking structures. The two typical arrangements of BLGs, AB and AA, are considered in this article. AB-BLG exhibits many discrete energy-loss peaks, which correspond to the quantization of electron energies. On the other hand, the AA-BLG spectra possess a unique and pronounced peak at low frequency. This peak represents the collective excitation of the entire low-frequency Landau states. The dependence of the energy-loss peaks on the momentum transfer and the magnetic field strength is presented. Accordingly, two kinds of plasmon modes produced by the layer stacking are clearly distinguished.

cond-mat.mes-hall↗

arXiv2013

Effects of transverse electric fields on Landau subbands in bilayer zigzag graphene nanoribbons

The magnetoelectronic properties of quasi-one-dimensional zigzag graphene nanoribbons are investigated by using the Peierls tight-binding model. Quasi-Landau levels (QLLs), dispersionless Landau subbands within a certain region of k-space, are resulted from the competition between magnetic and quantum confinement effects. In bilayer system, the interlayer interactions lead to two groups of QLLs, one occurring at the Fermi level and the other one occurring at higher energies. Transverse electric fields are able to distort energy spectrum, tilt two groups of QLLs and cause semiconductor-metal transition. From the perspective of wave functions, the distribution of electrons is explored, and the evolution of Landau states under the influence of electric fields is clearly discussed. More interestingly, the band mixing phenomena exhibited in the energy spectrum are related to the state mixing, which can be apparently seen in the wave functions. The density of states, which could be verified through surface inspections and optical experiments, such as scanning tunneling spectroscopy and absorption spectroscopy, is provided at last.

cond-mat.mes-hall↗

arXiv2012

Anisotropy of π-plasmon Dispersion Relation of AA-stacked Graphite

The dispersion relation of the high energy optical π-plasmons of simple hexagonal intrinsic graphite was calculated within the self-consistent-field approximation. The plasmon frequency ω_p is determined as functions of the transferred momentum $q_{\parallel}$ along the hexagonal plane in the Brillouin zone and its perpendicular component $q_z$. These plasmons are isotropic within the plane in the long wavelength limit. As the in-plane transferred momentum is increased, the plasmon frequency strongly depends on its magnitude and direction (ϕ). With increasing angle, the dispersion relation within the hexagonal plane is gradually changed from quadratic to nearly linear form. There are many significant differences for the π-plasmon dispersion relations between 2D graphene and 3D AA-stacked graphite. They include $q_\parallel$- and ϕ-dependence and π-plasmon bandwidth. This result reveals that interlayer interaction could enhance anisotropy of in-plane π-plasmons. For chosen $\textbf{q}_\parallel$, we also obtain the plasmon frequency as a function of $q_z$ and show that there is an upper bound on $q_z$ for plasmons to exist in graphite. Additionally, the group velocity for plasmon propagation along the perpendicular direction may be positive or negative depending on the choice of $\textbf{q}_\parallel$. Consequently, the forward and backward propagation of π-plasmons in AA-stacked graphite in which the energy flow is respectively parallel or antiparallel to the transferred momentum, can be realized. The backward flowing resonance is an intrinsic property of AA-stacked graphite, arising from the energy band structure and the interlayer coupling.

cond-mat.mtrl-sci↗

arXiv2010

Plasma Excitations in Graphene: Their Spectral Intensity and Temperature Dependence in Magnetic Field

In this paper, we calculated the dielectric function, the loss function, the magnetoplasmon dispersion relation and the temperature-induced transitions for graphene in a uniform perpendicular magnetic field B. The calculations were performed using the Peierls tight-binding model to obtain the energy band structure and the random-phase approximation to determine the collective plasma excitation spectrum. The single-particle and collective excitations have been precisely identified based on the resonant peaks in the loss function. The critical wave vector at which plasmon damping takes place is clearly established. This critical wave vector depends on the magnetic field strength as well as the levels between which the transition takes place. The temperature effects were also investigated. At finite temperature, there are plasma resonances induced by the Fermi distribution function. Whether such plasmons exist is mainly determined by the field strength, temperature, and momentum. The inelastic light scattering spectroscopies could be used to verify the magnetic field and temperature induced plasmons.

cond-mat.mes-hall↗

arXiv2010

Optical transitions between Landau levels: AA-stacked bilayer graphene

The low-frequency optical excitations of AA-stacked bilayer graphene are investigated by the tight-binding model. Two groups of asymmetric LLs lead to two kinds of absorption peaks resulting from only intragroup excitations. Each absorption peak obeys a single selection rule similar to that of monolayer graphene. The excitation channel of each peak is changed as the field strength approaches a critical strength. This alteration of the excitation channel is strongly related to the setting of the Fermi level. The peculiar optical properties can be attributed to the characteristics of the LL wave functions of the two LL groups. A detailed comparison of optical properties between AA-stacked and AB-stacked bilayer graphenes is also offered. The compared results demonstrate that the optical properties are strongly dominated by the stacking symmetry. Furthermore, the presented results may be used to discriminate AABG from MG, which can be hardly done by STM.

cond-mat.mes-hall↗