arXiv subjects

Ping Zhang

Publications and source records attributed to Ping Zhang.

At least 541 records · Page 30Linked to original sources

arXiv2012

Thermodynamic properties and structural stability of thorium dioxide

Using density functional theory (DFT) calculations, we have systematically investigated the thermodynamic properties and structural stabilities of thorium dioxide (ThO$_2$). Based on the calculated phonon dispersion curves, we calculate the thermal expansion coefficient, bulk modulus, and heat capacities at different temperatures for ThO$_2$ under the quasi-harmonic approximation. All the results are in good agreement with corresponding experiments proving the validity of our methods. Our theoretical studies can help people more clearly understand the thermodynamic behaviors of ThO$_2$ at different temperatures. In addition, we have also studied possible defect formations and diffusion behaviors of helium in ThO$_2$, to discuss its structural stability. It is found that in intrinsic ThO$_2$ without any Fermi energy shifts, the interstitial Th$_i^{4+}$ defect other than oxygen or thorium vacancies, interstitial oxygen, and any kinds of Frenkel pairs, is most probable to form with an energy release of 1.74 eV. However, after upshifting the Fermi energy, the formation of the other defects also becomes possible. For helium diffusion, we find that only through the thorium vacancy can it happen with the small energy barrier of 0.52 eV. Otherwise, helium atoms can hardly incorporate or diffuse in ThO$_2$. Our results indicate that people should prevent upshifts of the Fermi energy of ThO$_2$ to avoid the formation of thorium vacancies and so as to prevent helium caused damages.

cond-mat.mtrl-sci↗

arXiv2012

Magnetoexcitons and optical absorption of bilayer-structured topological insulators

Optical absorption properties of magnetoexcitons in topological insulator bilayers under a strong magnetic field are theoretically studied. A general analytical formula of optical absorption selection rule is obtained in the noninteracting as well as Coulomb intra-Landau-level interacting cases, which remarkably helps to interpret the resonant peaks in absorption spectroscopy and the corresponding formation of Dirac-type magnetoexcitons. We also discuss the optical absorption spectroscopy of magnetoexcitons in the presence of inter-Landau-level Coulomb interaction, which becomes more complex. Our results could be detected in the magneto-optical experiments.

cond-mat.mes-hall↗

arXiv2012

Quasiparticle states and quantum interference induce by magnetic impurities on a two-dimensional topological superconductor

We theoretically study the effect of localized magnetic impurities on two-dimensional topological superconductor (TSC). We show that the local density of states (LDOS) can be tuned by the effective exchange field $m$, the chemical potential $μ$ of TSC, and the distance $Δr$ as well as relative spin angle $α$ between two impurities. The changes in $Δr$ between two impurities alter the interference and result in significant modifications to the bonding and antibonding states. Furthermore, the bound-state spin LDOS induced by single and double magnetic impurity scattering, the quantum corrals, and the quantum mirages are also discussed. Finally, we briefly compare the impurities in TSC with those in topological insulators.

cond-mat.supr-con↗

arXiv2012

Probing crossover from analogous weak antilocalization to localization by an Aharonov-Bohm interferometer on topological insulator surface

We propose a scanning tunneling microscopy Aharonov-Bohm (AB) interferometer on the surface of a topological insulator (TI) to probe the crossover from analogous weak antilocalization (WAL) to weak localization (WL) phenomenon via the AB oscillations in spin-resolved local density of states (LDOS). Based on our analytical and numerical results, we show that with increasing the energy gap of TI surface states, the $Φ_{0}/2$=$hc/2e$ periodic AB oscillations in spin-resolved LDOS gradually transit into the $Φ_{0}$ periodic oscillations.

cond-mat.mes-hall↗

arXiv2012

Transport properties of dense deuterium-tritium plasmas

Consistent descriptions of the equation of states, and information about transport coefficients of deuterium-tritium mixture are demonstrated through quantum molecular dynamic (QMD) simulations (up to a density of 600 g/cm$^{3}$ and a temperature of $10^{4}$ eV). Diffusion coefficients and viscosity are compared with one component plasma model in different regimes from the strong coupled to the kinetic one. Electronic and radiative transport coefficients, which are compared with models currently used in hydrodynamic simulations of inertial confinement fusion, are evaluated up to 800 eV. The Lorentz number is also discussed from the highly degenerate to the intermediate region.

cond-mat.mtrl-sci↗

arXiv2012

Adsorption and dissociation of H$_{2}$O monomer on ceria(111): Density functional theory calculations

The adsorption properties of isolated H$_{2}$O molecule on stoichiometric and reduced (with on-surface oxygen vacancy) ceria(1111) surfaces at low coverage are theoretically investigated by using density-functional-theory+\emph{U} calculations and \textit{ab initio} molecular dynamics simulations. We identify the most stable adsorption configurations on these two kinds of surfaces, which form two hydrogen bonds between the water molecule and the oxide surface. The electronic structures indicate that the hybridization of the molecular orbitals of water and surface-layer O-2\emph{p} states dominates the interactions between adsorbate and substrate. The barrier of 0.51 eV for water diffusion on the stoichiometric surface implies the inertia of water unless up to a high temperature of 600 K, which is confirmed by the molecular dynamics simulations. For the reduced surface, we find that the oxygen vacancy obviously enhances the interaction. Moreover, it is facilitated for water to dissociate into H and OH species with a hydroxyl surface formed, instead of oxidizing the reduced surface with the production of hydrogen gas. In addition, the molecular dynamics simulations at low temperature 100 K confirm the dissociation process.

cond-mat.mtrl-sci↗

arXiv2012

Phonon spectrum and bonding properties of Bi$_{2}$Se$_{3}$: Role of strong spin-orbit interaction

Phonon dispersions of one typical three-dimensional topological insulator Bi$_{2}$Se$_{3}$ have been studied within density functional theory. The soft modes of two acoustic branches along the $Z$$-$$F$ and $Γ$$-$$F$ directions within the pure local density approximation will transit to show imaginary frequency oscillating after including the spin-orbit interaction (SOI). Similar phenomenon has also been observed for Bi$_{2}$Te$_{3}$. Besides, we have found that the weak van der Waals forces between two Se1 layers in Bi$_{2}$Se$_{3}$ are strengthened by turning on the SOI.

cond-mat.mtrl-sci↗

arXiv2012

First-principles study of native point defects in topological insulator Bi$_2$Se$_3$

The \emph{p}-type Bi$_{2}$Se$_{3}$ is much desirable as a promising thermoelectric material and topological insulator, while the naturally grown Bi$_{2}$Se$_{3}$ is always \emph{n}-type doped by native point defects. Here we use first-principles calculations to identify the origin of the \emph{n}-type tendency in bulk Bi$_{2}$Se$_{3}$: The Se vacancies (V$_\text{Se1}$ and V$_\text{Se2}$) and Se$_{\text{Bi}}$ antisite dominate the donorlike doping with low formation energy, while the predisposed Bi$_{\text{Se1}}$ defect results in the pair of V$_\text{Se1}$ and Bi interstitial, which is also a donor rather than an acceptor. Moreover, for Bi$_{2}$Se$_{3}$(111) surface, we find that the band structures modulated by the defects explicitly account for the existing experimental observations of \emph{n}-type preference.

cond-mat.mtrl-sci↗

arXiv2012

Topological properties of Sb(111) surface: A density functional theory study

By using first-principles plane wave calculations, we systematically study the electronic properties of the thin film of antimony in (111) orientation. Considering the spin-orbit interaction, for stoichiometric surface, the topological states keep robust for six bilayers, and can be recovered in the three bilayer film, which are guarantied by time-reversal symmetry and inverse symmetry. For reduced surface doped by Bi or Mn atom, localized 3-fold symmetric features can be identified. Moreover, the non-trivial topological states stand for non-magnetic substituted Bi atom, while can be eliminated by adsorbed or substituted magnetic Mn atom.

cond-mat.mtrl-sci↗

arXiv2012

Quantum Corrals and Quantum Mirages on the Surface of a Topological Insulator

We study quantum corrals on the surface of a topological insulator (TI). Different resonance states induced by nonmagnetic (NM), antiferromagnetic (AFM), and ferromagnetic (FM) corrals are found. Intriguingly, the spin is clearly energy-resolved in a FM corral, which can be effectively used to operate surface carrier spins of TI. We also show that an observable quantum mirage of a magnetic impurity can be projected from the occupied into the empty focus of a FM elliptic corral, while in NM and AFM corrals the mirage signal becomes negligibly weak. In addition, the modulation of the interaction between two magnetic impurities in the quantum corrals is demonstrated. These prominent effects may be measured by spin-polarized STM experiments.

cond-mat.mes-hall↗

arXiv2012

Topological phases and fractional excitations of the exciton condensate in a special class of bilayer systems

We study the exciton condensate in zero temperature limit in a special class of electron-hole bilayer systems adjacent to insulating ferromagnetic films. With the self-consistent mean-field approximation, we find that the Rashba spin-orbit interaction in the electron and hole layers can induce the p \pm ip or p pairing states depending on the different magnetization of the overlapped ferromagnetic films. Correspondingly, the topologically nontrivial or trivial phases emerge. Furthermore, in the topologically nontrivial phase, the quasiparticle excitations of the U(1) vortex are attached to fractional quantum numbers and obey Abelian statistics.

cond-mat.mes-hall↗

arXiv2011

Aharonov-Bohm oscillations in the local density of topological surface states

We study Aharonov-Bohm (AB) oscillations in the local density of states (LDOS) for topological insulator (TI) and conventional metal Au(111) surfaces with spin-orbit interaction, which can be probed by spin-polarized scanning tunneling microscopy. We show that the spacial AB oscillatory period in the total LDOS is a flux quantum $Φ_{0}\mathtt{=}hc/e$ (weak localization) in both systems. Remarkably, an analogous weak antilocalization with $Φ_{0}/2$ periodic spacial AB oscillations in spin components of LDOS for TI surface is observed, while it is absent in Au(111).

cond-mat.mes-hall↗

arXiv2011

Multiple scattering theory of quasiparticles on a topological insulator surface

A general partial-wave multiple scattering theory for scattering from cylindrically symmetric potentials on a topological insulator (TI) surface is developed. As an application, the cross sections for a single scatterer and two scatterers are discussed. We find that the symmetry of differential cross section is reduced and the backscattering is allowed for massive Dirac fermions on gapped TI surface. Remarkably, a sharp resonance peak at the band edge of the gapped TI is found in the total cross section $Λ_{tot}$, which may offer a useful way to determine the gap (as well as the effective mass of quasiparticles) on TI surface. We show that the interference effect is obvious in cross sections during the quasiparticle scattering between the scatterer pair, and additional resonance peaks are introduced in $Λ_{tot}$ when the higher partial waves are taken into account.

cond-mat.mes-hall↗

arXiv2011

First-principles calculations of phase transition, elasticity, and thermodynamic properties for TiZr alloy

tructural transformation, pressure dependent elasticity behaviors, phonon, and thermodynamic properties of the equiatomic TiZr alloy are investigated by using first-principles density-functional theory. Our calculated lattice parameters and equation of state for $α$ and $ω$ phases as well as the phase transition sequence of $α$$\mathtt{\rightarrow}$$ω$$\mathtt{\rightarrow}$$β$ are consistent well with experiments. Elastic constants of $α$ and $ω$ phases indicate that they are mechanically stable. For cubic $β$ phase, however, it is mechanically unstable at zero pressure and the critical pressure for its mechanical stability is predicted to equal to 2.19 GPa. We find that the moduli, elastic sound velocities, and Debye temperature all increase with pressure for three phases of TiZr alloy. The relatively large $B/G$ values illustrate that the TiZr alloy is rather ductile and its ductility is more predominant than that of element Zr, especially in $β$ phase. Elastic wave velocities and Debye temperature have abrupt increase behaviors upon the $α$$\mathtt{\rightarrow}$$ω$ transition at around 10 GPa and exhibit abrupt decrease feature upon the $ω$$\mathtt{\rightarrow}$$β$ transition at higher pressure. Through Mulliken population analysis, we illustrate that the increase of the \emph{d}-band occupancy will stabilize the cubic $β$ phase. Phonon dispersions for three phases of TiZr alloy are firstly presented and the $β$ phase phonons clearly indicate its dynamically unstable nature under ambient condition. Thermodynamics of Gibbs free energy, entropy, and heat capacity are obtained by quasiharmonic approximation and Debye model.

cond-mat.mtrl-sci↗

arXiv2011

Structural and electronic properties of ScnOm (n=1~3, m=1~2n) clusters: Theoretical study using screened hybrid density functional theory

The structural and electronic properties of small scandium oxide clusters ScnOm (n = 1 - 3, m = 1 - 2n) are systematically studied within the screened hybrid density functional theory. It is found that the ground states of these scandium oxide clusters can be obtained by the sequential oxidation of small "core" scandium clusters. The fragmentation analysis demonstrates that the ScO, Sc2O2, Sc2O3, Sc3O3, and Sc3O4 clusters are especially stable. Strong hybridizations between O-2p and Sc-3d orbitals are found to be the most significant character around the Fermi level. In comparison with standard density functional theory calculations, we find that the screened hybrid density functional theory can correct the wrong symmetries and yield more precise description for the localized 3d electronic states of scandium.

physics.atm-clus↗

arXiv2011

Structures and magnetic properties of ZnO nanoislands

Using first-principles calculations, we systematically study the atomic structures and electronic properties for two dimensional triangular ZnO nanoislands that are graphite-like with monolayer and bilayer thickness. We find that the monolayer ZnO nanoisland with O terminated zigzag edges is magnetic at its ground state, with the magnetism coming from the O edge states. The other monolayer and bilayer ZnO nanoislands with different edge structures are all nonmagnetic at their ground states. It is further revealed that for different ZnO nanoislands, their magnetic properties are quite dependent on their sizes, with larger nanoislands having larger magnetic moments.

cond-mat.mtrl-sci↗

arXiv2011

Influences of Al doping on the electronic structure of Mg(0001) and dissociation property of H2

By using the density functional theory method, we systematically study the influences of the doping of an Al atom on the electronic structures of the Mg(0001) surface and dissociation behaviors of H2 molecules. We find that for the Al-doped surfaces, the surface relaxation around the doping layer changes from expansion of a clean Mg(0001) surface to contraction, due to the redistribution of electrons. After doping, the work function is enlarged, and the electronic states around the Fermi energy have a major distribution around the doping layer. For the dissociation of H2 molecules, we find that the energy barrier is enlarged for the doped surfaces. Especially, when the Al atom is doped at the first layer, the energy barrier is enlarged by 0.30 eV. For different doping lengths, however, the dissociation energy barrier decreases slowly to the value on a clean Mg(0001) surface when the doping layer is far away from the top surface. Our results well describe the electronic changes after Al-doping for the Mg(0001) surface, and reveal some possible mechanisms for improving the resistance to corrosion of the Mg(0001) surface by doping of Al atoms.

physics.chem-ph↗

arXiv2011

Dissociation of hydrogen molecules on the clean and hydrogen-preadsorbed Be(0001) surface

Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes for hydrogen molecules on the clean and hydrogen-preadsorbed Be(0001) surfaces. It is found that the most energetically favored dissociation channel for H2 molecules on the clean Be surface is at the surface top site, with the minimum energy barrier of 0.75 eV. It is further found that after dissociation, hydrogen atoms do not like to cluster with each other, as well as to penetrate into subsurface sites. For the hydrogen-preadsorbed Be(0001) surface, the smallest dissociation energy barrier for H2 molecules is found to be 0.50 eV, which is smaller than the dissociation energy barrier on a clean Be(0001) surface. The critical dependence of the dissociation energy barriers for H2 molecules on their horizontal distances from the preadsorbed hydrogen atom is revealed. Our studies well describe the adsorption behaviors of hydrogen on the Be(0001) surface.

cond-mat.mtrl-sci↗