arXiv subjects

Ming-Fa Lin

Publications and source records attributed to Ming-Fa Lin.

At least 55 records · Page 3Linked to original sources

arXiv2017

Novel Magnetic Quantization of Bismuthene

The generalized tight-binding model, being based on the spin-dependent sublattices, is developed to explore the magnetic quantization of monolayer bismuthene. The sp$^{3}$ orbital hybridizations, site energies, nearest and next-nearest hopping integrals, spin-orbital interactions and magnetic field (${B_{z}}$ ${\hat{z}}$) are taken into account simultaneously. There exist three groups of low-lying Landau levels (LLs), in which they are mainly from the (6p$_{x}$,6p$_{y}$,6p$_{z}$) orbitals, and only the first group belongs to the unoccupied conduction states. Furthermore, each group is further split into the spin-up- and spin-down-dominated subgroups. The six subgroups present the rich and unique $B_{z}$-dependent LL energy spectra, covering the specific or arc-shaped $% B_{z}$-dependences, the normal/irregular spin-split energies, and the non-crossing/crossing/anti-crossing behaviors. Specially, the second group of valence LLs near the Fermi level can create the frequent inter-subgroup LL anti-crossings since the main and side modes are comparable. The main features of energy spectra can create the special structures in density of states.

cond-mat.mtrl-sci↗

arXiv2017

Chiral symmetry classes and Dirac nodal lines in three-dimensional layered systems

We study the existence and stability of Dirac nodal lines in three-dimensional layered systems, whose layers individually have Dirac nodal points protected by chiral (sublattice) symmetry. The model system we consider is the rhombohedral stack of graphene layers with each layer subjected to a uniform external potential that respects either AIII or BDI classes. From the Hamiltonians in either classes, a pair of nontrivial spiraling Dirac nodal lines can be derived. The results are reasonable in accord to the topological classification of gapless phases for codimension $2$. The nodal lines approach each other as the magnitude of the potential increases, revealing their annihilation due to the fact that regarding the full system their topological invariants are cancelled out.

cond-mat.mes-hall↗

arXiv2017

Diversified essential properties in halogenated graphenes

The significant halogenation effects on the essential properties of graphene are investigated by the first-principles method. The geometric structures, electronic properties, and magnetic configurations are greatly diversified under the various halogen adsorptions. Fluorination, with the strong multi-orbital chemical bondings, can create the buckled graphene structure, while the other halogenations do not change the planar σ bonding in the presence of single-orbital hybridization. Electronic structures consist of the carbon-, adatom- and (carbon, adatom)-dominated energy bands. All halogenated graphenes belong to hole-doped metals except that fluorinated systems are middle-gap semiconductors at sufficiently high concentration. Moreover, the metallic ferromagnetism is revealed in certain adatom distributions. The unusual hybridization-induced features are clearly evidenced in many van Hove singularities of the density of states. The structure- and adatom-enriched essential properties are compared with the measured results, and potential applications are also discussed.

cond-mat.mes-hall↗

arXiv2017

Evolution and dimensional crossover from the bulk subbands in ABC-stacked graphene to a three-dimensional Dirac cone structure in rhombohedral graphite

The band structure of ABC-stacked N-layer graphene comprises topologically corresponding flat surface and gapped bulk subbands, as a consequence of the unique stacking configuration. In this paper, the bulk subbands are for the first times ever obtained for arbitrary N. A non-perturbative effective Hamiltonian closed in the bulk subspace is derived and used. The gapped bulk subbands are shown to evolve towards the zero energy with increasing N and in the infinite limit, they touch linearly along a circle. This outcome is a manifestation of the dimensional crossover to a three-dimensional Dirac cone structure known to exist in the bulk of rhombohedral graphite. The Dirac points, forming continuous nodal lines in a spiraling fashion, are projected onto the circle, within which the surface subbands are confined and flatten.

cond-mat.mes-hall↗

arXiv2017

Landau quantization in buckled monolayer GaAs

Magneto-electronic properties of buckled monolayer GaAs is studied by the developed generalized tight-binding model, considering the buckled structure, multi-orbital chemical bondings, spin-orbit coupling, electric field, and magnetic field simultaneously. Three group of spin-polarized Landau levels (LLs) near the Fermi level are induced by the magnetic quantization, whose initial energies, LL degeneracy, energy spacings, magnetic-field-dependence, and spin polarization are investigated. The Landau state probabilities describing the oscillation patterns, localization centers, and node regularities of the dominated/minor orbitals are analyzed, and their energy-dependent variations are discussed. The given density of states directly reflects the main features of the LL energy spectra in the structure, height, number, and frequency of the spin-polarized LL peaks. The electric field causes the monotonous/nonmonotonous LL energy dispersions, LL crossing, gap modulation, phase transition and spin splitting enhancement. The complex gap modulations and phase transitions based on the competition between magnetic and electric fields are explored in detail by the phase diagram. The field-controlled gap modulations and phase transitions are helpful in designing the top-gated and phase-change electronic devices. These predicted magneto-electronic properties could be verified by scanning tunneling spectroscopy measurements.

physics.comp-ph↗

arXiv2017

Electronic and optical properties of graphite-related systems

A systematic review is made for the AA-, AB- and ABC-stacked graphites. The generalized tight-binding model, accompanied with the effective-mass approximation and the Kubo formula, is developed to investigate electronic and optical properties in the presence/absence of a uniform magnetic field. The unusual electronic properties cover the stacking-dependent Dirac-cone structures, the significant energy widths along the stacking direction, the Landau subbands (LSs) crossing the Fermi level, the $B_0$-dependent LS energy spectra with crossings and anti-crossings, and the monolayer- or bilayer-like Landau wavefunctions. There exist the configuration-created special structures in density of states and optical spectra. Three kinds of graphites quite differ from one another in the available inter-LS excitation channels, including the number, frequency, intensity and structures of absorption peaks. The dimensional crossover presents the main similarities and differences between graphites and graphenes; furthermore, the quantum confinement enriches the magnetic quantization phenomena in carbon nanotubes and graphene nanoribbons. The cooperative/competitive relations among the interlayer atomic interactions, dimensions and magnetic quantization are responsible for the diversified essential properties. Part of theoretical predictions are consistent with the experimental measurements.

cond-mat.mes-hall↗

arXiv2017

Stacking-enriched magneto-transport properties of few-layer graphenes

The quantum Hall effects in the sliding bilayer graphene and AAB-stacked trilayer system are investigated by the Kubo formula and the generalized tight-binding model. The various stacking configurations can greatly diversify the magnetic quantization and thus create the rich and unique transport properties. The quantum conductivities are very sensitive to the Fermi energy and magnetic-field strength. The diverse features cover the specific non-integer conductivities, the integer conductivities with the distinct steps, the splitting-created reduction and complexity of quantum conductivity, a vanishing or non-zero conductivity at the neutral point, and the well-like, staircase, composite, and abnormal plateau structures in the field-dependencies. Such stacking-dependent characteristics mainly originate from the crossing, anticrossing and splitting Landau-level energy spectra and three kinds of quantized modes.

cond-mat.mtrl-sci↗

arXiv2017

Adatom Doping-Enriched Geometric and Electronic Properties of Pristine Graphene: a Method to Modify the Band Gap

We have investigated the way in which the concentration and distribution of adatoms affect the geometric and electronic properties of graphene. Our calculations were based on the use of first principle under the density functional theory which reveal various types of $π$-bonding. The energy band structure of this doped graphene material may be explored experimentally by employing angle-resolved photo-emission spectroscopy (ARPES) for electronic band structure measurements and scanning tunneling spectroscopy (STS) for the density-of-states (DOS) both of which have been calculated and reported in this paper. Our calculations show that such adatom doping is responsible for the destruction or appearance of the Dirac cone structure.

cond-mat.mes-hall↗

arXiv2017

Geometric and electronic properties of graphene-related systems: Chemical bondings

This work presents a systematic review of the feature-rich essential properties in graphene-related systems using the first-principles method. The geometric and electronic properties are greatly diversified by the number of layers, the stacking configurations, the sliding-created configuration transformation, the rippled structures, and the distinct adatom adsorptions. The top-site adsorptions can induce the significantly buckled structures, especially for hydrogen and fluorine adatoms. The electronic structures consist of the carbon-, adatom- and (carbon, adatom)-dominated energy bands. There exist the linear, parabolic, partially flat, sombrero-shaped and oscillatory band, accompanied with various kinds of critical points. The semi-metallic or semiconducting behaviors of graphene systems are dramatically changed by the multi- or single-orbital chemical bondings between carbons and adatoms. Graphene oxides and hydrogenated graphenes possess the tunable energy gaps. Fluorinated graphenes might be semiconductors or hole-doped metals, while other halogenated systems belong to the latter. Alkali- and Al-doped graphenes exhibit the high-density free electrons in the preserved Dirac cones. The ferromagnetic spin configuration is revealed in hydrogenated and halogenated graphenes under certain distributions. Specifically, Bi nano-structures are formed by the interactions between monolayer graphene and buffer layer. Structure and adatom-enriched essential properties are compared with the measured results, and potential applications are also discussed.

physics.chem-ph↗

arXiv2016

Alkali-induced rich properties in graphene nanoribbons: Chemical bonding

The alkali-adsorbed graphene nanoribbons exhibit the feature-rich electronic and magnetic properties. From the first-principles calculations, there are only few adatom-dominated conduction bands, and the other conduction and valence bands are caused by carbon atoms. A lot of free electrons are revealed in the occupied alkali- and carbon-dependent conduction bands. Energy bands are sensitive to the concentration, distribution and kind of adatom and the edge structure, while the total linear free carrier density only relies on the first one. These mainly arise from a single $s-2p_z$ orbital hybridization in the adatom-carbon bond. Specifically, zigzag systems can present the anti-ferromagnetic ordering across two edges, ferromagnetic ordering along one edge and non-magnetism, being reflected in the edge-localized energy bands with or without spin splitting. The diverse energy dispersions contribute many special peaks in density of states. The critical chemical bonding and the distinct spin configuration could be verified from the experimental measurements.

cond-mat.mes-hall↗

arXiv2016

Magnetoelectronic and optical properties of nonuniform graphene nanoribbons

The electronic and optical properties of nonuniform bilayer graphene nanoribbons are worth investigating as they exhibit rich magnetic quantization. Based on our numerical results, their electronic and optical properties strongly depend on the competition between magnetic quantization, lateral confinement, and stacking configuration. The results of our calculations lead to four categories of magneto-electronic energy spectra, namely monolayer-like, bilayer-like, coexistent, and irregular quasi-Landau-level like. Various types of spectra described in this paper are mainly characterized by unusual spatial distributions of wave functions in the system under study. In our paper, we demonstrate that these unusual quantized modes lead to the appearance of such diverse magneto-optical spectra. Moreover, the investigation of the density of states in our model leads to the appearance of many prominent symmetric and weakly asymmetric peaks. The almost well-behaved quasi-Landau levels exhibit high-intensity peaks with specific selection rules, and the distorted energy subbands present numerous low-intensity peaks without any selection rules.

physics.comp-ph↗

arXiv2016

Optical Properties of Graphene in Magnetic and Electric fields

Optical properties of graphene are explored by using the generalized tight-binding model. The main features of spectral structures, the form, frequency, number and intensity, are greatly enriched by the complex relationship among the interlayer atomic interactions, the magnetic quantization and the Coulomb potential energy. Absorption spectra have the shoulders, asymmetric peaks and logarithmic peaks, coming from the band-edge states of parabolic dispersions, the constant-energy loops and the saddle points, respectively. The initial forbidden excitation region is only revealed in even-layer AA stacking systems. Optical gaps and special structures can be generated by an electric field. The delta-function-like structures in magneto-optical spectra, which present the single, twin and double peaks, are associated with the symmetric, asymmetric and splitting Landau-level energy spectra, respectively. The single peaks due to the non-tilted Dirac cones exhibit the nearly uniform intensity. The AAB stacking possesses more absorption structures, compared to the other stackings. The diverse magneto-optical selection rules are mainly determined by the well-behaved, perturbed and undefined Landau modes. The frequent anti-crossings in the magnetic- and electric-field-dependent energy spectra lead to the increase of absorption peaks and the reduced intensities. Part of theoretical calculations are consistent with the experimental measurements, and the others need further detailed examinations.

physics.comp-ph↗

arXiv2016

Feature-rich electronic properties of aluminum-doped graphenes

The electronic properties of aluminum-doped graphenes enriched by multi-orbital hybridizations are investigated using first-principles calculations. The feature-rich electronic structures exhibit the quasi-rigid red shifts of the carbon-created energy bands, the Al-dominated valence and conduction bands, and many free electrons in the conduction Dirac cone. These are directly reflected in the special structures of density of states (DOS). The Al- and alkali-induced high free carrier densities are almost the same. There exist certain important differences among the Al-, alkali- and halogen-doped grapehenes, such as, the buckled or planar graphene, the preserved or seriously distorted Dirac cone, the existence of the adatom-dominated valence bands, the free electrons or holes, the degenerate or splitting spin-related states, and the simple or complicated peaks in DOS. The similarities and differences mainly come from the diverse orbital hybridizations in adatom-C bonds, as indicated from the atom-dominated bands, the spatial charge distributions and the orbital-projected DOS.

cond-mat.mtrl-sci↗

arXiv2016

Coulomb excitations of monolayer germanene

The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbital coupling and the buckled structure. The collective and single- particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e-h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e-h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes.

physics.comp-ph↗

arXiv2016

Electronic and optical properties of graphene nanoribbons in external fields

A review work is done for electronic and optical properties of graphene nanoribbons in magnetic, electric, composite, and modulated fields. Effects due to the lateral confinement, curvature, stacking, non-uniform subsystems and hybrid structures are taken into account. The special electronic properties, induced by complex competitions between external fields and geometric structures, include many one-dimensional parabolic subbands, standing waves, peculiar edge-localized states, width- and field-dependent energy gaps, magnetic-quantized quasi-Landau levels, curvature-induced oscillating Landau subbands, crossings and anti-crossings of quasi-Landau levels, coexistence and combination of energy spectra in layered structures, and various peak structures in the density of states. There exist diverse absorption spectra and different selection rules, covering edge-dependent selection rules, magneto-optical selection rule, splitting of the Landau absorption peaks, intragroup and intergroup Landau transitions, as well as coexistence of monolayer-like and bilayer-like Landau absorption spectra. Detailed comparisons are made between the theoretical calculations and experimental measurements. The predicted results, the parabolic subbands, edge-localized states, gap opening and modulation, and spatial distribution of Landau subbands, have been verified by various experimental measurements.

cond-mat.mes-hall↗

arXiv2015

$π$-bonding-dominated energy gaps in graphene oxides

Chemical bondings of graphene oxides with oxygen concentration from 1\% to 50\% are investigated using first-principle calculations. Energy gaps are mainly determined by the competition of orbital hybridizations in C-C, O-O, and C-O bonds. They are very sensitive to the changes in oxygen concentration and distributions. There exists five types of $π$ bondings during the variation from the full to vanishing adsorptions, namely the complete termination, the partial suppression, the 1D bonding, the deformed planar bonding, and the well-behaved one. They can account for the finite and gapless characteristics, corresponding to the O-concentrations of $>$25\% and $<$3\%, respectively. The feature-rich chemical bondings dominate band structures and density of states, leading to diverse electronic properties.

cond-mat.mtrl-sci↗

arXiv2015

Novel Magnetic Quantization of sp$^{3}$ Bonding in Monolayer Tinene

A generalized tight-binding model, which is based on the subenvelope functions of the different sublattices, is developed to explore the novel magnetic quantization in monolayer gray tin. The effects due to the $sp^{3}$ bonding, the spin-orbital coupling, the magnetic field and the electric field are simultaneously taken into consideration. The unique magneto-electronic properties lie in two groups of low-lying Landau levels, with different orbital components, localization centers, state degeneracy, spin configurations, and magnetic- and electric-field dependences. The first and second groups mainly come from the $5p_{z}$ and ($5p_{x}$,$5p_{y}$) orbitals, respectively. Their Landau-level splittings are, respectively, induced by the electric field and spin-orbital interactions. The intragroup anti-crossings are only revealed in the former. The unique tinene Landau levels are absent in graphene, silicene and germanene.

cond-mat.mes-hall↗

arXiv2015

Configuration- and concentration-dependent electronic properties of hydrogenated graphene

The electronic properties of hydrogenated graphenes are investigated with the first-principles calculations. Geometric structures, energy bands, charge distributions, and density of states (DOS) strongly depend on the different configurations and concentrations of hydrogen adatoms. Among three types of optimized periodical configurations, only in the zigzag systems the band gaps can be remarkably modulated by H-concentrations. There exist middle-gap semiconductors, narrow-gap semiconductors, and gapless systems. The band structures exhibit the rich features, including the destruction or recovery of the Dirac-cone structure, newly formed critical points, weakly dispersive bands, and (C,H)-related partially flat bands. The orbital-projected DOS are evidenced by the low-energy prominent peaks, delta-function-like peaks, discontinuous shoulders, and logarithmically divergent peaks. The DOS and spatial charge distributions clearly indicate that the critical bondings in C-C and C-H is responsible for the diversified properties.

cond-mat.mtrl-sci↗