arXiv subjects

Cheng-Peng Chang

Publications and source records attributed to Cheng-Peng Chang.

7 recordsLinked to original sources

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

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

An analytical study of electronic properties of ABC-stacking multilayer graphene

We present an analytical model to study the electronic properties, including full band structure, low energy dispersions around the Dirac point and density of states of the ABC-stacking $N$-layer graphene (ABCNLG). An ABCNLG can be simulated by a linear atomic chain with $2N$ atoms. With only nearest-neighbor inter- and intra-layer hopping integrals taken into account, the Hamiltonian representation is a complex $2N \times 2N$ tridiagonal matrix $H_0$. Through a unitary transformation, we can reduce the $2N \times 2N$ Hamiltonian matrix into two real $N \times N$ tridiagonal matrices $\mathbb{H}_{s}$ and $\mathbb{H}_{a}$, i. e., $H_0=\mathbb{H}_{s} \oplus \mathbb{H}_{a} $. What's more, the two matrices satisfy the relation $\mathbb{H}_{a}=-\mathbb{H}_{s}$. As a result, energy spectrum associated with $\mathbb{H}_{s}$ and $\mathbb{H}_{s}$ have the relation $λ_{a}=-λ_{s}$. Such a characteristic is reflected on the energy dispersions and density of states. Our model can be applied to explore the basic properties of linear chain model and the eigenvalue problem of the tridiagonal matrices.

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↗

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

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

Dynamical conductivity of gated AA-stacking multilayer graphene with spin-orbital coupling

An efficient method with no numerical diagonalization of a huge Hamiltonian matrix and calculation of a tedious Green's function is proposed to acquire the exact energy spectrum and dynamical conductivity in a gated AA-stacking $N$-layer Graphene (AANLG) with the intrinsic spin-orbital coupling (SOC). $2N \times 2N$ tight-binding Hamiltonian matrix, velocity operator and Green's function representation of an AANLG are simultaneously reduced to $N$ $2\times 2$ diagonal block matrices through a proper transformation matrix. A gated AANLG with intrinsic SOC is reduced to $N$ graphene-like layers. The energy spectrum of a graphene-like layer is $E= \varepsilon _{\bot}\pm \varepsilon_{||}$. $ \varepsilon _{\bot}$ depends on the interlayer interaction, gated voltage and layer number. $ \varepsilon_{||}=\sqrt{E_{MG}^2+ Δ^2}$, where $E_{MG}$ is the energy spectrum of a monolayer graphene and $ Δ$ is the magnitude of intrinsic SOC. More importantly, by inserting the diagonal block velocity operator and Green's function representation in the Kubo formula, the exact dynamical conductivity of an AANLG is shown to be $σ= Σ_{j=1} ^N σ_j$, the sum of the dynamical conductivity of $N$ graphene-like layers. The analytical form of $σ_j$ is presented and the dependence of $σ_j$ on $\varepsilon_{\bot}$, $Δ$, and chemical potential is clearly demonstrated. Moreover, the effect of Rashba SOC on the electronic properties of an AANLG is explored with the exact energy spectrum presented.

cond-mat.mes-hall↗