Peng Cheng

Peng Cheng
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Peng Cheng

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Physics - Superconductivity (17)
Physics - Materials Science (14)
Physics - Mesoscopic Systems and Quantum Hall Effect (13)
Physics - Strongly Correlated Electrons (6)
Computer Science - Databases (5)
General Relativity and Quantum Cosmology (3)
Computer Science - Learning (1)
Mathematics - Information Theory (1)
Mathematics - Optimization and Control (1)
Computer Science - Information Theory (1)
Physics - Computational Physics (1)
Computer Science - Networking and Internet Architecture (1)
Physics - Chemical Physics (1)
High Energy Physics - Theory (1)

Publications Authored By Peng Cheng

The remarkably strong chemical adsorption behaviors of nitric oxide on magnesia (001) film deposited on metal substrate have been investigated by employing periodic density functional calculations with Van der Waals corrections. The molybdenum supported magnesia (001) show significantly enhanced adsorption properties and the nitric oxide is chemisorbed strongly and preferably trapped in flat adsorption configuration on metal supported oxide film, due to the substantially large adsorption energies and transformation barriers. The analysis of Bader charges, projected density of states, differential charge densities, electron localization function, highest occupied orbital and particular orbital with largest Mg-NO-Mg bonding coefficients, are applied to reveal the electronic adsorption properties and characteristics of bonding between nitric oxide and surface as well as the bonding within the hybrid structure. Read More

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 $H_0$. Read More

We present the successful synthesis of single-atom-thick borophene nanoribbons (BNRs) by self-assembly of boron on Ag(110) surface. The scanning tunneling microscopy (STM) studies reveal high quality BNRs: all the ribbons are along the [-110] direction of Ag(110), and can run across the steps on the surface. The width of ribbons is distributed in a narrow range around 10. Read More

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. Read More

Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band structures can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn4, ZrSiS, TlTaSe2 and PbTaSe2. Read More

For decades, the crowdsourcing has gained much attention from both academia and industry, which outsources a number of tasks to human workers. Existing works considered improving the task accuracy through voting or learning methods, they usually did not fully take into account reducing the latency of the task completion. When a task requester posts a group of tasks (e. Read More

Privacy-preserving average consensus aims to guarantee the privacy of initial states and asymptotic consensus on the exact average of the initial value. In existing work, it is achieved by adding and subtracting variance decaying and zero-sum random noises to the consensus process. However, there is lack of theoretical analysis to quantify the degree of the privacy protection. Read More

Privacy-preserving data aggregation in ad hoc networks is a challenging problem, considering the distributed communication and control requirement, dynamic network topology, unreliable communication links, etc. The difficulty is exaggerated when there exist dishonest nodes, and how to ensure privacy, accuracy, and robustness against dishonest nodes remains an open issue. Different from the widely used cryptographic approaches, in this paper, we address this challenging problem by exploiting the distributed consensus technique. Read More

Recently, with the rapid development of mobile devices and the crowdsourcing platforms, the spatial crowdsourcing has attracted much attention from the database community. Specifically, spatial crowdsourcing refers to sending a location-based request to workers according to their positions, and workers need to physically move to specified locations to conduct tasks. Many works have studied task assignment problems in spatial crowdsourcing, however, their problem definitions are quite different from each other. Read More

Micro-burst traffic is not uncommon in data centers. It can cause packet dropping, which results in serious performance degradation (e.g. Read More

Treating the cosmological constant as a thermodynamic pressure, we investigate the critical behavior of a Kerr-Newman-AdS black hole system. The critical points for the van der Waals like phase transition are numerically solved. The highly accurate fitting formula for them is given and is found to be dependent of the charge $Q$ and angular momentum $J$. Read More

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. Read More

Spatial crowdsourcing refers to a system that periodically assigns a number of location-based workers with spatial tasks nearby (e.g., taking photos or videos at some spatial locations). Read More

Boron is the fifth element in the periodic table and possesses rich chemistry second only to carbon. A striking feature of boron is that B12 icosahedral cages occur as the building blocks in bulk boron and many boron compounds. This is in contrast to its neighboring element, carbon, which prefers 2D layered structure (graphite) in its bulk form. Read More

With the rapid development of mobile devices and crowdsourcing platforms, the spatial crowdsourcing has attracted much attention from the database community. Specifically, the spatial crowdsourcing refers to sending location-based requests to workers, based on their current positions. In this paper, we consider a spatial crowdsourcing scenario, in which each worker has a set of qualified skills, whereas each spatial task (e. Read More

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. Read More

In the extended phase space, the $d$-dimensional singly spinning Kerr-AdS black holes exhibit the van der Waals's phase transition and reentrant phase transition. Since the black hole system is a single characteristic parameter thermodynamic system, we show that the form of the critical point can be uniquely determined by the dimensional analysis. When $d=4$, we get the analytical critical point. Read More

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. Read More

We performed a scanning tunneling microscopy and spectroscopy (STM/STS) study on the electronic structures of of root(3)Xroot(3)-silicene on Ag(111). We find that the coupling strength of root(3)Xroot(3)-silicene with Ag(111) substrate is variable at different regions, giving rise to notable effects in experiments. These evidences of decoupling or variable interaction of silicene with the substrate are helpful to in-depth understanding of the structure and electronic properties of silicene. Read More

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. Read More

In this paper, the shadow casted by the rotating black hole inspired by noncommutative geometry is investigated. In addition to the dimensionless spin parameter $a/M_{0}$ with $M_{0}$ black hole mass and inclination angle $i$, the dimensionless noncommutative parameter $\sqrt{\vartheta}/M_{0}$ is also found to affect the shape of the black hole shadow. The result shows that the size of the shadow slightly decreases with the parameter $\sqrt{\vartheta}/M_{0}$, while the distortion increases with it. Read More

Silicene monolayers grown on Ag(111) surfaces demonstrate a band gap that is tunable by oxygen adatoms from semimetallic to semiconducting type. By using low-temperature scanning tunneling microscopy, it is found that the adsorption configurations and amounts of oxygen adatoms on the silicene surface are critical for band-gap engineering, which is dominated by different buckled structures in R13xR13, 4x4, and 2R3x2R3 silicene layers. The Si-O-Si bonds are the most energy-favored species formed on R13xR13, 4x4, and 2R3x2R3 structures under oxidation, which is verified by in-situ Raman spectroscopy as well as first-principles calculations. Read More

With the rapid development of mobile devices and the crowdsourcig platforms, the spatial crowdsourcing has attracted much attention from the database community, specifically, spatial crowdsourcing refers to sending a location-based request to workers according to their positions. In this paper, we consider an important spatial crowdsourcing problem, namely reliable diversity-based spatial crowdsourcing (RDB-SC), in which spatial tasks (such as taking videos/photos of a landmark or firework shows, and checking whether or not parking spaces are available) are time-constrained, and workers are moving towards some directions. Our RDB-SC problem is to assign workers to spatial tasks such that the completion reliability and the spatial/temporal diversities of spatial tasks are maximized. Read More

The "multilayer silicene" films were grown on Ag(111), with increasing thickness above 30 monolayers (ML). We found that the "multilayer silicene" is indeed a bulk Si(111) film. Such Si film on Ag(111) always exhibits a root(3)xroot(3) honeycomb superstructure on surface. Read More

In layered superconductors, Josephson junctions may be formed within the unit cell due to sufficiently low interlayer coupling. These intrinsic Josephson junction (iJJ) systems have attracted considerable interest for their application potential in quantum computing as well as efficient sources of THz radiation, closing the famous "THz gap". So far, iJJ have been demonstrated in single-band, copper-based high-Tc superconductors, mainly in Ba-Sr-Ca-Cu-O. Read More

Copper and Nickel impurities have been doped into the iron pnictide superconductor Ba0.6K0.4Fe2As2. Read More

We performed low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) studies on the electronic properties of (R3xR3)R30{\deg} phase of silicene on Ag(111) surface. We found the existence of Dirac Fermion chirality through the observation of -1.5 and -1. Read More

Organic superconductors are unique materials with a crystal structure made primarily of a complex carbon based network, an element associated directly with life, which were postulated to have a high critical temperature, $T_{C}$, even above room temperature, from a theoretical viewpoint. Pressure plays an essential role in the study of superconductivity in such organic materials, including creation of the first organic superconductor as well as the achievement of the highest $T_{C}$ of 14.2 K for charge transfer salts and 38 K for metal-doped fullerides. Read More

The (r3xr3)R30{\deg} honeycomb of silicene monolayer on Ag(111) was found to undergo a phase transition to two types of mirror-symmetric boundary-separated rhombic phases at temperatures below 40 K by scanning tunneling microscopy. The first-principles calculations reveal that weak interactions between silicene and Ag(111) drive the spontaneous ultra buckling in the monolayer silicene, forming two energy-degenerate and mirror-symmetric (r3xr3)R30{\deg} rhombic phases, in which the linear band dispersion near Dirac point (DP) and a significant gap opening (150 meV) at DP were induced. The low transition barrier between these two phases enables them interchangeable through dynamic flip-flop motion, resulting in the (r3xr3)R30{\deg} honeycomb structure observed at high temperature. Read More

The intercalated layered nitride $\beta$-HfNCl has attracted much attention due to the high superconducting transition temperature up to 25.5 K. Electrons can be introduced into $\beta$-$M$NCl ($M$=Zr and Hf) through alkali-metals intercalation to realize the superconductivity. Read More

Silicene, a sheet of silicon atoms in a honeycomb lattice, was proposed to be a new Dirac-type electron system similar as graphene. We performed scanning tunneling microscopy and spectroscopy studies on the atomic and electronic properties of silicene on Ag(111). An unexpected $\sqrt{3}\times \sqrt{3}$ reconstruction was found, which is explained by an extra-buckling model. Read More

In the search for evidence of silicene, a two-dimensional honeycomb lattice of silicon, it is important to obtain a complete picture for the evolution of Si structures on Ag(111), which is believed to be the most suitable substrate for growth of silicene so far. In this work we report the finding and evolution of several monolayer superstructures of silicon on Ag(111) depending on the coverage and temperature. Combined with first-principles calculations, the detailed structures of these phases have been illuminated. Read More

We propose a first-order method for stochastic strongly convex optimization that attains $O(1/n)$ rate of convergence, analysis show that the proposed method is simple, easily to implement, and in worst case, asymptotically four times faster than its peers. We derive this method from several intuitive observations that are generalized from existing first order optimization methods. Read More

We propose a general theory on the standing waves (quasiparticle interference pattern) caused by the scattering of surface states off step edges in topological insulators, in which the extremal points on the constant energy contour of surface band play the dominant role. Experimentally we image the interference patterns on both Bi$_2$Te$_3$ and Bi$_2$Se$_3$ films by measuring the local density of states using a scanning tunneling microscope. The observed decay indices of the standing waves agree excellently with the theoretical prediction: In Bi$_2$Se$_3$, only a single decay index of -3/2 exists; while in Bi$_2$Te$_3$ with strongly warped surface band, it varies from -3/2 to -1/2 and finally to -1 as the energy increases. Read More

Signal-to-leakage-and-noise ratio (SLNR) is a promising criterion for linear precoder design in multi-user (MU) multiple-input multiple-output (MIMO) systems. It decouples the precoder design problem and makes closed-form solution available. In this letter, we present a new linear precoding scheme by slightly relaxing the SLNR maximization for MU-MIMO systems with multiple data streams per user. Read More

Low temperature specific heat has been measured in optimally doped and highly overdoped non-superconducting BaFe$_{2-x}$TM$_x$As$_{2}$ ($TM$ = Co and Ni) single crystals. By using the data of the overdoped samples, we successfully removed the phonon contribution of the optimally doped ones, and derived the electronic specific heat coefficient $\gamma_e$. Remarkably, we found a continuing temperature dependent $\gamma_e(T)$ which follows the quadratic relation $\gamma_e=\gamma_0+\alpha T^2$ in the low temperature limit. Read More

The recent theoretical prediction and experimental realization of topological insulators (TI) has generated intense interest in this new state of quantum matter. The surface states of a three-dimensional (3D) TI such as Bi_2Te_3, Bi_2Se_3 and Sb_2Te_3 consist of a single massless Dirac cones. Crossing of the two surface state branches with opposite spins in the materials is fully protected by the time reversal (TR) symmetry at the Dirac points, which cannot be destroyed by any TR invariant perturbation. Read More

Resistivity, Hall effect, magnetoresistance and DC magnetization were measured in Mn and Zn doped Ba$_{0.5}$K$_{0.5}$Fe$_{2}$As$_{2}$ samples. Read More

We report a comprehensive investigation of the suppression of the critical temperature Tc of NdFeAs(OF) single crystal by alpha-particle irradiation. Our data indicate that irradiation defects produce both nonmagnetic and magnetic scattering, resulting in the Kondo-like excess resistance $\Delta\rho(T)\propto ln T$ over 2 decades in temperatures above $T_c$. Despite high densities of irradiation defects, the dose at which $T_c$ is suppressed to zero is comparable to that for MgB2 but is well above the corresponding values for cuprates. Read More

Magnetization and its relaxation have been measured in $Ba(Fe_{1-x}Co_x)_2As_2$ single crystals at various doping levels ranging fromvery underdoped to very overdoped regimes. Sizable magnetization relaxation rate has been observed in all samples, indicating a moderate vortex motion and relatively small characteristic pinning energy. Detailed analysis leads to the following conclusions: (1) A prominent second-peak (SP) effect was observed in the samples around the optimal doping level (x $\approx$ 0. Read More

Sr2VO{3-delta}FeAs superconductors with different oxygen deficiencies have been successfully fabricated. It is found that the superconducting transition temperature drops down monotonically with the increase of oxygen deficiency. The diminishing of superconductivity is accompanied by the enhancement of residual resistivity, indicating an unraveled scattering effect induced by the oxygen deficiency. Read More

Superconductivity at about 15.6 K was achieved in Tb_{1-x}Ca_xFeAsO by partially substituting Tb^{3+} with Ca^{2+} in the nominal doping region x = 0.40 \sim 0. Read More

We report direct imaging of standing waves of the nontrivial surface states of topological insulator Bi$_2$Te$_3$ by using a low temperature scanning tunneling microscope. The interference fringes are caused by the scattering of the topological states off Ag impurities and step edges on the Bi$_2$Te$_3$(111) surface. By studying the voltage-dependent standing wave patterns, we determine the energy dispersion $E(k)$, which confirms the Dirac cone structure of the topological states. Read More

We have measured the magnetic field and temperature dependence of specific heat on $Bi_2Sr_{2-x}La_xCuO_{6+\delta}$ single crystals in wide doping and temperature regions. The superconductivity related specific heat coefficient $\gamma_{sc}$ and entropy $S_{sc}$ are determined. It is found that $\gamma_{sc}$ has a hump-like anomaly at $T_c$ and behaves as a long tail which persists far into the normal state for the underdoped samples, but for the heavily overdoped samples the anomaly ends sharply just near $T_c$. Read More

Low-temperature specific heat (SH) and resistivity were measured on Ba(Fe_{1-x}Co_x)_2As_2 single crystals in wide doping region. A sizeable residual specific heat coefficient \gamma_0 was observed in the low temperature limit of all samples. The specific heat jump near T_c, i. Read More

By substituting the Fe with the 4d and 5d-transition metals Rh, Ir and Pd in SrFe_2As_2, we have successfully synthesized a series of superconductors SrFe_{2-x}M_xAs_2 (M = Rh, Ir and Pd) and explored the phase diagrams of them. The systematic evolution of the lattice constants indicated that part of the Fe ions were successfully replaced by the transition metals Rh, Ir and Pd. By increasing the doping content of Rh, Ir and Pd, the antiferromagnetic state of the parent phase is suppressed progressively and superconductivity is induced. Read More

The superconductor Sr4V2O6Fe2As2 with transition temperature at 37.2 K has been fabricated. It has a layered structure with the space group of p4/nmm, and with the lattice constants a = 3. Read More

Superconductivity was achieved in Ti-doped iron-arsenide compound Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). Read More

We report a systematic investigation, together with a theoretical analysis, of the resistivity and Hall effect in single crystals of Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$, over a wide doping range. We find a surprisingly great disparity between the relaxation rates of the holes and the electrons, in excess of an order of magnitude in the low-doping, low-temperature regime. The ratio of the electron to hole mobilities diminishes with temperature and doping (away from the magnetically ordered state) and becomes more conventional. Read More