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Ping Zhang

Publications and source records attributed to Ping Zhang.

At least 613 records · Page 34Linked to original sources
arXiv2009

Magnetization in two-dimensional electron gas in a perpendicular magnetic field: the roles of edge states and spin-orbit coupling

We study the de Haas--van Alphen (dHvA) oscillations in the magnetization of a two-dimensional electron gas (2DEG) under the influence of the edge states and/or the Rashba spin-orbit interaction (SOI). The boundaries of the systems lift partially the degeneracies of Landau levels (LL's) and the resulting edge states lead to the changes of both the center and the amplitude of the sawtoothlike magnetization oscillation. The SOI mixes the spin-up and spin-down states of neighboring LL's into two unequally spaced energy branches. The inclusion of SOI changes the well-defined sawtooth pattern of the dHvA oscillations in the magnetization. The weaker the magnetic field is, the larger is the change of the dHvA oscillations due to the edge effect and/or the spin-orbit coupling. Some theoretical results are compared with the experimental data.

cond-mat.mes-hall↗
arXiv2008

Topological edge states and quantum Hall effect in the Haldane model

We study the topological edge states of the Haldane's graphene model with zigzag/armchair lattice edges. The Harper equation for solving the energies of the edge states is derived. The results show that there are two edge states in the bulk energy gap, corresponding to the two zero points of the Bloch function on the complex-energy Riemann surface. The edge-state energy loops move around the hole of the Riemann surface in appropriate system parameter regimes. The quantized Hall conductance can be expressed by the winding numbers of the edge states, which reflects the topological feature of the Haldane model.

cond-mat.mes-hall↗
arXiv2008

Spin Hall effect in the kagome lattice with Rashba spin-orbit interaction

We study the spin Hall effect in the kagomé lattice with Rashba spin-orbit coupling. The conserved spin Hall conductance $σ_{xy}^{s}$ (see text) and its two components, i.e., the conventional term $σ_{xy}^{s0}$ and the spin-torque-dipole term $σ_{xy}^{sτ}$, are numerically calculated, which show a series of plateaus as a function of the electron Fermi energy $ε_{F}$. A consistent two-band analysis, as well as a Berry-phase interpretation, is also given. We show that these plateaus are a consequence of the various Fermi-surface topologies when tuning $ε_{F}$. In particular, we predict that compared to the case with the Fermi surface encircling the $\mathbfΓ$ point in the Brillouin zone, the amplitude of the spin Hall conductance with the Fermi surface encircling the $\mathbf{K}$ points is twice enhanced, which makes it highly meaningful in the future to systematically carry out studies of the $\mathbf{K}$-valley spintronics.

cond-mat.mes-hall↗
arXiv2008

Adsorption and dissociation of O$_{2}$ at Be(0001): First-principles prediction of an energy barrier on the adiabatic potential energy surface

The adsorption and dissociation of O$_{2}$ molecules at the Be(0001) surface is studied by using density-functional theory within the generalized gradient approximation and a supercell approach. The physi- and chemisorbed molecular precursor states are identified to be along the parallel and vertical channels, respectively. It is shown that the HH-Z (see the text for definition) channel is the most stable channel for the molecular chemisorption of O$_{2}$. The electronic and magnetic properties of this most stable chemisorbed molecular state are studied, which shows that the electrons transfer forth and back between the spin-resolved antibonding $π^{\ast}$ molecular orbitals and the surface Be $sp$ states. A distinct covalent weight in the molecule-metal bond is also shown. The dissociation of O$_{2}$ is determined by calculating the adiabatic potential energy surfaces, wherein the T-Y channel is found to be the most stable and favorable for the dissociative adsorption of O$_{2}$. Remarkably, we predict that unlike the other simple $sp$ metal surfaces such as Al(111) and Mg(0001), the \textit{adiabatic} dissociation process of O$_{2}$ at Be(0001) is an activated type with a sizeable energy barrier.

cond-mat.mtrl-sci↗
arXiv2008

Quasienergy spectra of a charged particle in planar honeycomb lattices

The low energy spectrum of a particle in planar honeycomb lattices is conical, which leads to the unusual electronic properties of graphene. In this letter we calculate the quasienergy spectra of a charged particle in honeycomb lattices driven by a strong AC field, which is of fundamental importance for its time-dependent dynamics. We find that depending on the amplitude, direction and frequency of external field, many interesting phenomena may occur, including band collapse, renormalization of velocity of ``light'', gap opening etc.. Under suitable conditions, with increasing the magnitude of the AC field, a series of phase transitions from gapless phases to gapped phases appear alternatively. At the same time, the Dirac points may disappear or change to a line. We suggest possible realization of the system in Honeycomb optical lattices.

cond-mat.other↗
arXiv2008

Edge states and the integer quantum Hall effect of spin-chiral ferromagnetic kagome lattice with a general spin coupling

The chiral edge states and the quantized Hall conductance (QHC) in the two-dimensional kagomé lattice with spin anisotropies included in a general Hund's coupling region are studied. This kagomé lattice system is periodic in the $x$ direction but has two edges in the $y$ direction. Numerical results show that the strength of the Hund's coupling, as well as the spin chirality, affects the edge states and the corresponding QHC. Within the topological edge theory, we give the expression of the QHC with the winding number of the chiral edge states on the Riemman surface. This expression is also compaired with that within the topological bulk theory and they are found to keep consistent with each other.

cond-mat.mes-hall↗
arXiv2008

Orbital magnetization and its effects in spin-chiral ferromagnetic kagome lattice in the general spin-coupling region

The orbital magnetization and its effects on the two-dimensional kagomé lattice with spin anisotropies included in the general Hund's coupling region have been theoretically studied. The results show that the strength of the Hund's coupling, as well as the spin chirality, contributes to the orbital magnetization $\mathcal{M}$. Upon varying both these parameters, it is found that the two parts of $\mathcal{M}$, i.e., the conventional part $\mathbf{M}_{c}$ and the Berry-phase correction part $\mathbf{M}_Ω$, oppose each other. The anomalous Nernst conductivity is also calculated and a peak-valley structure as a function of the electron Fermi energy is obtained.

cond-mat.mes-hall↗
arXiv2007

First-principles LDA+U and GGA+U study of plutonium oxides

The electronic structure and properties of PuO$_{2}$ and Pu$_{2}$O$_{3}$ have been studied from first principles by the all-electron projector-augmented-wave (PAW) method. The local density approximation (LDA)+$U$ and the generalized gradient approximation (GGA)+$U$ formalism have been used to account for the strong on-site Coulomb repulsion among the localized Pu $5f$ electrons. We discuss how the properties of PuO$_{2}$ and Pu$_{2}$O$_{3}$ are affected by the choice of $U$ as well as the choice of exchange-correlation potential. Also, oxidation reaction of Pu$_{2}$O$_{3}$, leading to formation of PuO$_{2}$, and its dependence on $U$ and exchange-correlation potential have been studied. Our results show that by choosing an appropriate $U$ it is promising to correctly and consistently describe structural, electronic, and thermodynamic properties of PuO$_{2}$ and Pu$_{2}$O$_{3}$, which enables it possible the modeling of redox process involving Pu-based materials.

cond-mat.mtrl-sci↗
arXiv2007

Edge states and the integer quantum Hall conductance in spin-chiral ferromagnetic kagome lattice

We investigate the chiral edge states in the two-dimensional ferromagntic kagomé lattice with spin anisotropies included. The system is periodic in the $x$ direction but has two edges in the $y$ direction. The Harper equation for solving the energies of edge states is derived. We find that there are two edge states in each bulk energy gap, corresponding to two zero points of the Bloch function on the complex-energy Riemann surface (RS). The edge-state energy loops parametrized by the momentum $k_{x}$ cross the holes of the RS. When the Fermi energy lies in the bulk energy gap, the quantized Hall conductance is given by the winding number of the edge states across the holes, which reads as $σ_{xy}^{\text{edge}}$=$-\frac{e^{2}}{h}% $sgn$(\sinϕ) $, where $ϕ$ is the spin chiral parameter (see text). This result keeps consistent with that based on the topological bulk theory.

cond-mat.mes-hall↗
arXiv2007

Equation of state for shock-compressed porous molybdenum from first-principles mean-field potential calculations

The Hugoniot curves for shock-compressed molybdenum with initial porosities of 1.0, 1.26, 1.83, and 2.31 are theoretically investigated. The method of calculations combines the first-principles treatment for zero- and finite-temperature electronic contribution and the mean-field-potential approach for the ion-thermal contribution to the total free energy. Our calculated results reproduce the Hugoniot properties of porous molybdenum quite well. At low porosity, in particular, the calculations show a complete agreement with the experimental measurements over the full range of data. For the two large porosity values of 1.83 and 2.31, our results are well in accord with the experimental data points up to the particle velocity of 3.5 km/s, and tend to overestimate the shock-wave velocity and Hugoniot pressure when further increasing the particle velocity. In addition, the temperature along the principal Hugoniot is also extensively investigated for porous molybdenum.

cond-mat.mtrl-sci↗
arXiv2007

Atomic oxygen adsorption and incipient oxidation of the Pb(111) surface: A density-functional theory study

We study the atomic oxygen adsorption on Pb(111) surface by using density-functional theory within the generalized gradient approximation and a supercell approach. The atomic and energetic properties of purely on-surface and subsurface oxygen structures at the Pb(111) surface are systematically investigated for a wide range of coverages and adsorption sites. The fcc and tetra-II sites (see the text for definition) are found to be energetically preferred for the on-surface and subsurface adsorption, respectively, in the whole range of coverage considered. The on-surface and subsurface oxygen binding energies monotonically increase with the coverage, and the latter is always higher than the former, thus indicating the tendency to the formation of oxygen islands (clusters) and the higher stability of subsurface adsorption. The on-surface and subsurface diffusion-path energetics of atomic oxygen, and the activation barriers for the O penetration from the on-surface to the subsurface sites are presented at low and high coverages. In particular, it is shown that the penetration barrier from the on-surface hcp to the subsurface tetra-I site is as small as 65 meV at low coverage ($Θ$=0.25). The other properties of the O/Pb(111) system, including the charge distribution, the lattice relaxation, the work function, and the electronic density of states, are also studied and discussed in detail, which consistently show the gradually stabilizing ionic O-Pb bond with increase of the oxygen coverage.

cond-mat.mtrl-sci↗
arXiv2007

Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition

We study the disentanglement of two spin qubits which interact with a general XY spin-chain environment. The dynamical process of the disentanglement is numerically and analytically investigated in the vicinity of quantum phase transition (QPT) of the spin chain in both weak and strong coupling cases. We find that the disentanglement of the two qubits is in general enhanced greatly when the environmental spin chain is exposed to QPT. We give a detailed analysis to facilitate the understanding of the QPT-enhanced decaying behavior of the disentanglement factor. Furthermore, the scaling behavior in the disentanglement dynamics is also revealed and analyzed.

quant-ph↗
arXiv2007

Orbital magnetization and its effect in antiferromagnets on the distorted fcc lattice

We study the intrinsic orbital magnetization (OM) in antiferromagnets on the distorted face-centered-cubic lattice. The combined lattice distortion and spin frustration induce nontrivial $k$-space Chern invariant, which turns to result in profound effects on the OM properties. We derive a specific relation between the OM and the Hall conductivity, according to which it is found that the intrinsic OM vanishes when the electron chemical potential lies in the Mott gap. The distinct behavior of the intrinsic OM in the metallic and insulating regions is shown. The Berry phase effects on the thermoelectric transport is also discussed.

cond-mat.mes-hall↗
arXiv2007

Conserved spin Hall conductance in two dimensional electron gas in a perpendicular magnetic field

Using the microscopic theory of the conserved spin current [Phys. Rev. Lett. \textbf{96}, 076604 (2006)], we investigate the spin Hall effect in the two dimensional electron gas system with a perpendicular magnetic field. The spin Hall conductance $σ_{μν}^{s}$ as a response to the electric field consists of two parts, i.e., the conventional part $σ_{μν}^{s0}$ and the spin torque dipole correction $σ_{μν}^{sτ}$. It is shown that the spin-orbit coupling competes with Zeeman splitting by introducing additional degeneracies between different Landau levels at certain values of magnetic field. These degeneracies, if occurring at the Fermi level, turn to give rise to resonances in both $σ_{μν}^{s0}$ and $σ_{μν}^{sτ}$ in spin Hall conductance. Remarkably, both of these two components have the same sign in the wide range of variation in the magnetic field, which result in an overall enhancement of the total spin Hall current. In particular, the magnitude of $σ_{μν}^{sτ}$ is much larger than that of $σ_{μν}^{s0}$ around the resonance.

cond-mat.mes-hall↗
arXiv2007

Orbital magnetization and its effects in spin-chiral ferromagnetic Kagome lattice

Recently, Berry phase in the semiclassical dynamical of Bloch electrons has been found to make a correction to the phase-space density of states and a general multi-band formula for finite-temperature orbital magnetization has been given [Phys. Rev. Lett. \textbf{97}, 026603 (2006)], where the orbital magnetization $\mathcal{M}$ consists of two parts, i.e., the conventional part $M_{c}$ and the Berry-phase correction part $M_Ω$. Using this general formula, we theoretically investigate the orbital magnetization and its effects on thermoelectric transport and magnetic susceptibility properties of the two-dimensional \textit{kagomé} lattice with spin anisotropies included. The study in this paper is highly interesting by the occurrence of nonzero Chern number in the lattice. The spin chirality parameter $ϕ$ (see text) results in profound effects on the orbital magnetization properties. It is found that the two parts in orbital magnetization opposite each other. In particular, we show that $M_{c}$ and $M_Ω$ yield the paramagnetic and diamagnetic responses, respectively. It is further shown that the orbital magnetization displays fully different behavior in the metallic and insulating regions, which is due to the different roles $M_{c}$ and $M_Ω$ play in these two regions. The anomalous Nernst conductivity is also calculated, which displays a peak-valley structure as a function of the electron Fermi energy.

cond-mat.mes-hall↗
arXiv2007

On the blowing up of solutions to quantum hydrodynamic models on bounded domains

The blow-up in finite time for the solutions to the initial-boundary value problem associated to the multi-dimensional quantum hydrodynamic model in a bounded domain is proved. The model consists on conservation of mass equation and a momentum balance equation equivalent to a compressible Euler equations corrected by a dispersion term of the third order in the momentum balance. The proof is based on a-priori estimates for the energy functional for a new observable constructed with an auxiliary function, and it is shown that, under suitable boundary conditions and assumptions on the initial data, the solution blows up after a finite time.

math-ph↗
arXiv2007

First-Principles Calculation of Be(0001) Thin Films: Quantum Size Effect and Adsorption of Atomic Hydrogen

We have carried out first-principles calculations of Be(0001) thin films to study the oscillatory quantum size effects exhibited in the surface energy, work function, and binding energy of the atomic hydrogen monolayer adsorption. The prominent enhancement of the surface density of states at the Fermi level makes Be(0001) thin films more metallic compared to the crystalline Be. As a result, the calculated energetics of Be films and the properties of atomic H adsorption onto Be(0001) surface are featured by a quantum oscillatory behavior. Furthermore, The prominent change in the Be(0001) surface electronic structure by the atomic hydrogen adsorption has also been shown.

cond-mat.mtrl-sci↗