Showing papers in "Chinese Physics Letters in 2008"

Superconductivity at 55 K in Iron-Based F-Doped Layered Quaternary Compound Sm[O1-xFx] FeAs

Abstract: We report the superconductivity in iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crystal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides up to now.

Canonical Entropy and Phase Transition of Rotating Black Hole

Abstract: Recently, the Hawking radiation of a black hole has been studied using the tunnel effect method. The radiation spectrum of a black hole is derived. By discussing the correction to spectrum of the rotating black hole, we obtain the canonical entropy. The derived canonical entropy is equal to the sum of Bekenstein–Hawking entropy and correction term. The correction term near the critical point is different from the one near others. This difference plays an important role in studying the phase transition of the black hole. The black hole thermal capacity diverges at the critical point. However, the canonical entropy is not a complex number at this point. Thus we think that the phase transition created by this critical point is the second order phase transition. The discussed black hole is a five-dimensional Kerr-AdS black hole. We provide a basis for discussing thermodynamic properties of a higher-dimensional rotating black hole.

Thermoelectric Performance of Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate)

Abstract: Thermoelectric (TE) performances are systematically investigated for the pellets of poly(3,4-ethylenedioxythio-phene):poly(styrenesulfonate) (PEDOT:PSS) with different organic additives and heating process as organic TE materials. The electrical conductivity, Seebeck coefficient and thermal conductivity versus temperature are determined, respectively. It is found that there is no distinct change for the Seebeck coefficient among each sample with the additions of dimethyl sulfoxide and ethylene glycol. The thermal conductivity measured in a wide range of temperature indicates that the PEDOT:PSS pellet have an extremely low value. The highest figure of merit (ZT = 1.75 × 10−3) is observed at 270K among the PEDOT:PSS pellets.

Superconductivity in hole-doped (Sr(1-x)K(x))Fe(2)As(2)

Abstract: A series of layered (Sr1-xKx)Fe2As2 compounds with nominal x = 0-0.40 are synthesized by solid state reaction method. Similar to other parent compounds of iron-based pnictide superconductors, pure SrFe2As2 shows a strong resistivity anomaly near 210 K, which was ascribed to the spin-density-wave instability. The anomaly temperature is much higher than those observed in LaOFeAs and BaFe2As2, the two prototype parent compounds with ZrCuSiAs- and ThCr2Si2-type structures. K-doping strongly suppresses this anomaly and induces superconductivity. Like in the case of K-doped BaFe2As2, sharp superconducting transitions at Tc ~ 38 K is observed. We perform the Hall coefficient measurement, and confirm that the dominant carriers are hole-type. The carrier density is enhanced by a factor of 3 in comparison to F-doped LaOFeAs superconductor.

Multiple Nodeless Superconducting Gaps in (Ba 0.6 K 0.4 )Fe 2 As 2 Superconductor from Angle-Resolved Photoemission Spectroscopy

Abstract: High resolution angle-resolved photoemission measurements have been carried out to study the superconducting gap in the (Ba0.6K0.4)Fe2As2 superconductor with Te = 35 K. Two hole-like Fermi surface sheets around the I' point exhibit different superconducting gaps. The inner Fermi surface sheet shows larger (10 ~ 12 meV) and slightly momentum-dependent gap while the outer one has smaller (7 ~ 8meV) and nearly isotropic gap. The lack of gap node in both Fermi surface sheets favours s-wave superconducting gap symmetry. Superconducting gap opening is also observed at the M(π, π) point. The two Fermi surface spots near the M point are gapped below Te but the gap persists above Te. The rich and detailed superconducting gap information will provide key insights and constraints in understanding pairing mechanism in the iron-based superconductors.

Bianisotropy Picture of Higher Permeability at Higher Frequencies

Abstract: With an effective bianisotropy picture, high-frequency behaviours of different magnetic materials can be reconciled, and the higher permeability and higher resonance frequencies are achieved even in the GHz range. The validity of the bianisotropy picture is quantitatively verified by the in-plane anisotropic Fe34Co55Zr11 thin films. A prolate elliptical precession of the magnetization about its equilibrium direction is the key point, which can be induced by an artificial or an intrinsic bianisotropy system.

Nodal Gap in Fe-Based Layered Superconductor LaO 0.9 F 0.1-δ FeAs Probed by Specific Heat Measurements

Abstract: We report the specific heat measurements on the newly discovered Fe-based layered LaO0.9F0.1-δFeAs superconductor with the onset transition temperature Tc ≈ 28K. A nonlinear magnetic field dependence of the electronic specific heat coefficient γ(H) has been found in the low temperature limit, which is consistent with the prediction for a nodal superconductor. The maximum gap value Δ0 ≈ 3.4 ± 0.5 meV is derived by analysing γ(H) based on the d-wave model. We also detected the electronic specific heat difference between 9 T and 0 T in a wide temperature range, a specific heat anomaly can be clearly observed near Tc. The Debye temperature of our sample is determined to be about 315.7K. Our results suggest an unconventional mechanism for this new superconductor.

Transformation of Sign of Nonlinear Refraction between Mo(W)/S/Cu Planar Metal Clusters

Abstract: Optical nonlinear refractive properties of a series of Mo(W)/S/Cu planar square clusters are investigated using the Z-scan technique with the ns laser pulses at the wavelength of532nm. The result shows that the planar metal clusters containing the halogen ligands demonstrate the self-focusing effect, and the other planar metal clusters demonstrate the self-defocusing effect. These facts indicate that the halogen ligands can act as crucial factors in determining the sign of the nonlinear refraction of the Mo(W)/S/Cu planar metal clusters. The analysis of the experimental data shows that the planar clusters with halogen ligands possess greater refraction volume of the excited state than that of the ground state, while the other planar clusters possess the smaller refraction volume of the excited state than that of the ground state.

Three-Photon Resonant Nondegenerate Six-Wave Mixing in a Dressed Atomic System

Abstract: We report a three-photon resonant nondegenerate six-wave mixing (NSWM) in a dressed cascade five-level system It has advantages that phase match condition is not stringent and NSWM signal is enhanced tremendously due to the multiple resonance with the atomic transition frequencies In the presence of a strong coupling Held, the three-photon resonant NSWM spectrum exhibits Autler-Townes splitting This technique provides a spectroscopic tool for measuring not only the resonant frequency and dephasing rate but also the transition dipole moment between two highly excited atomic states

Element substitution effect in transition metal oxypnictide Re(O(1-x)F(x))TAs (Re=rare earth, T=transition metal)

Abstract: Different element substitution effects in transition metal oxypnictide Re(O1-xFx)TAs, with Re = La, Ce, Nd, Eu, Gd, Tm, T = Fe, Ni, Ru, are studied. Similar to the La- or Ce-based systems, we find that the pure NdOFeAs shows a strong resistivity anomaly near 145 K, which is ascribed to the spin-density-wave instability. Electron doping by F increases Tc to about 50 K. While in the case of Gd, Tc is reduced below 10 K. The tetragonal ZrCuSiAs-type structure could not be formed for Eu or Tm substitution in our preparing process. For the Ni-based case, although both pure and F-doped LaONiAs are superconducting, no superconductivity is found when La is replaced by Ce in both the cases, instead a ferromagnetic ordering transition is likely to form at low temperature in the undoped sample. We also synthesize LaO1-xFxRuAs and CeO1-xFxRuAs compounds. The metallic behaviour is observed down to 4K.

A Numerical Tackling on Sakiadis Flow with Thermal Radiation

Abstract: Momentum and energy laminar boundary layers of an incompressible fluid with thermal radiation about a moving plate in a quiescent ambient fluid are investigated numerically. Also, it has been underlined that the analysis of the roles of both velocity and temperature gradient at infinity is of key relevance for our results.

Temperature dependence of thermal conductivity of nanofluids

Abstract: Mechanism of thermal conductivity of nanofluids is analysed and calculated, including Brownian motion effects, particle agglomeration and viscosity, together influenced by temperature. The results show that only Brownian motion as reported is not enough to describe the temperature dependence of the thermal conductivity of nanofluids. The change of particle agglomeration and viscosity with temperature are also important factors. As temperature increases, the reduction of the particle surface energy would decrease the agglomeration of nanopar-ticles, and the reduction of viscosity would improve the Brownian motion. The results agree well with the experimental data reported.

A Special Eavesdropping on One-Sender Versus N-Receiver QSDC Protocol

Abstract: We analyse the security of a quantum secure direct communication (QSDC) protocol and find that an eavesdropper can utilize a special property of GHZ states to elicit all or part of the transmitted secrets without being detected. The particular attack strategy is presented in detail. We give an improved version of this protocol so that it can resist this attack.

Exact Periodic Solitary-Wave Solution for KdV Equation

Abstract: A new technique, the extended homoclinic test technique, is proposed to seek periodic solitary wave solutions of integrable systems. Exact periodic solitary-wave solutions for classical KdV equation are obtained using this technique. This result shows that it is entirely possible for the (1+1)-dimensional integrable equation that there exists a periodic solitary-wave.

Influence of Grain Size on Electrical and Optical Properties of InP Films

Abstract: InP film samples were prepared by spray pyrolysis technique using aqueous solutions of InCl3 and Na2HPO4, which were atomized with compressed air as carrier gas onto glass substrates at 500° C with different thicknesses of the films. It is found that the resistivity of the polycrystalline films strongly depends on the grain size. It is observed that the grain size of the films increase with the decrease of the energy band gap and strain of the film. The changes observed in the energy band gap and strain related to the film grain size of the films are discussed in detail.

Structural and Electrical Properties of PZT/PVDF Piezoelectric Nanocomposites Prepared by Cold-Press and Hot-Press Routes

Abstract: The 0-3 PZT/PVDF piezoelectric composites are prepared separately by hot-press and cold-press processes. The effects of the PZT content and the shaping-process on the composites are studied. The experimental results indicate that composites with 70% PZT nanopowders prepared by the hot-press method exhibit excellent piezoelectric and dielectric properties. The maxima of dss and e of the composites prepared by hot-press method are about 30% and 65% higher than those prepared by the cold-press method, respectively. This is mainly attributed to the favourable coupling of the two materials in the process of the hot press and the formation of the β-type PVDF, which possesses better electric properties.

Microchip Laser Feedback Interferometer with an Optical Path Multiplier

Abstract: We present a microchip laser feedback interferometer with an optical path multiplier to enhance the resolution of traditional laser feedback interferometers (LFI). The optical path multiplier has a unique device, i.e. diffusive reflector. As class B microchip lasers have extremely high sensitivity to laser feedback, the diffusive reflector can easily reflect or diffuse back the laser beam without much manual adjustment to the optical system, which ensures the system's easy-adjustment and practical feature. The optical path multiplier is a two-mirror system which enables the laser beam to reflect between the two mirrors by N times. When the target shifts a distance of Δd, the variation of the optical path will be about (AN × Δd). Thus the system's resolution is about 4N times as high as the traditional LFI. Under typical room conditions, the optical path multiplier can effectively enhance the system's resolution by more than 26 times as high as a traditional LFI system and even to the level of 0.1 nm.

Control Chaos in Hindmarsh—Rose Neuron by Using Intermittent Feedback with One Variable

Abstract: The mechanism of the famous phase compression is discussed, and it is used to control the chaos in the Hindmarsh-Rose (H-R) model. It is numerically confirmed that the phase compression scheme can be understood as one kind of intermittent feedback scheme, which requires appropriate thresholds and feedback coefficient, and the intermittent feedback can be realized with the Heaviside function. In the case of control chaos, the output variable (usually the voltage or the membrane potential of the neuron) is sampled and compared with the external standard signal of the electric electrode. The error between the sampled variable and the external standard signal of the electrode is input into the system only when the sampled variable surpasses the selected thresholds. The numerical simulation results confirm that the chaotic H-R system can be controlled to reach arbitrary n-periodical (n = 1, 2, 3, 4, 5, 6,...) orbit or stable state even when just one variable is feed backed into the system intermittently. The chaotic Chua circuit is also investigated to check its model independence and effectiveness of the schemes and the equivalence of the two schemes are confirmed again.

Thickness Dependence of Resistivity and Optical Reflectance of ITO Films

Abstract: Indium-tin-oxide (ITO) films deposited on crystalline silicon wafer and Corning glass are prepared by direct-current magnetron sputtering method at room temperature with various thicknesses. The thickness dependences of structure, resistance and optical reflectance of ITO films are characterized. The results show that when the film thickness is less than 40 nm, the resistivity and optical reflectance of the ITO film changes remarkably with thickness. The optoelectrical properties trend to stabilize when the thickness is over 55 nm. The GXRD result implies that the ITO film begins to crystallize if only the thickness is large enough.

Experimental Decoy State Quantum Key Distribution Over 120 km Fibre

Abstract: Decoy state quantum key distribution (QKD), being capable of beating PNS attack and being unconditionally secure, has become attractive recently. However, in many QKD systems, disturbances of transmission channel make the quantum bit error rate (QBER) increase, which limits both security distance and key bit rate of real-world decoy state QKD systems. We demonstrate the two-intensity decoy QKD with a one-way Faraday-Michelson phase modulation system, which is free of channel disturbance and keeps an interference fringe visibility (99%) long period, over a 120km single mode optical fibre in telecom (1550 nm) wavelength. This is the longest distance fibre decoy state QKD system based on the two-intensity protocol.

Demonstration of a 4H SiC Betavoltaic Nuclear Battery Based on Schottky Barrier Diode

Abstract: A 4H SiC betavoltaic nuclear battery is demonstrated. A Schottky barrier diode is utilized for carrier separation. Under illumination of Ni-63 source with an apparent activity of 4 mCi/cm2 an open circuit voltage of 0.49 V and a short circuit current density of 29.44 nA/cm2 are measured. A power conversion efficiency of 1.2% is obtained. The performance of the device is limited by low shunt resistance, backscattering and attenuation of electron energy in air and Schottky electrode. It is expected to be significantly improved by optimizing the design and processing technology of the device.

Viscous Cosmology and Thermodynamics of Apparent Horizon

Abstract: It is shown that the differential form of Friedmann equations of Friedman?Robertson?Walker (FRW) universe can be recast as a similar form of the first law ThdSh = dE+WdV of thermodynamics at the apparent horizon of FRW universe filled with the viscous fluid. It is also shown that by employing the general expression of temperature associated with the apparent horizon of FRW universe and assumed that the temperature Tm of the energy inside the apparent horizon is proportional to the horizon temperature Tm = bTh, we are able to show that the generalized second law of thermodynamics holds in the Einstein gravity provided .

Pseudogap and Superconducting Gap in Sm FeAs(O 1-x F x ) Superconductor from Photoemission Spectroscopy

Abstract: High resolution photoemission measurements are carried out on non-superconducting SmOFeAs parent compound and superconducting SmFeAs(O1-xFx) (x = 0.12, and 0.15) compounds. The momentum-integrated spectra exhibit a clear Fermi cutoff that shows little leading-edge shift in the superconducting state. A robust feature at 13meV is identified in all these samples. Spectral weight suppression near Ef with decreasing temperature is observed in both undoped and doped samples that points to a possible existence of a pseudogap in these Fe-based compounds.

Quantum Secret Sharing Protocol between Multiparty and Multiparty with Single Photons and Unitary Transformations

Abstract: We propose a scheme of quantum secret sharing between Alice's group and Bob's group with single photons and unitary transformations In the protocol, one member in Alice's group prepares a sequence of single photons in one of four different states, while other members directly encode their information on the sequence of single photons via unitary operations; after that, the last member sends the sequence of single photons to Bob's group Then Bob's, except for the last one, do work similarly Finally the last member in Bob's group measures the qubits If the security of the quantum channel is guaranteed by some tests, then the qubit states sent by the last member of Alice's group can be used as key bits for secret sharing It is shown that this scheme is safe

Conformal Invariance and Conserved Quantities of General Holonomic Systems

Abstract: Conformal invariance and conserved quantities of general holonomic systems are studied. A one-parameter infinitesimal transformation group and its infinitesimal transformation vector of generators are described. The definition of conformal invariance and determining equation for the system are provided. The conformal factor expression is deduced from conformal invariance and Lie symmetry. The necessary and sufficient condition, that conformal invariance of the system would be Lie symmetry, is obtained under the infinitesimal one-parameter transformation group. The corresponding conserved quantity is derived with the aid of a structure equation. Lastly, an example is given to demonstrate the application of the result.

Efficient Quantum Secure Direct Communication with Authentication

Abstract: Two protocols of quantum direct communication with authentication [Phys. Rev. A 73 (2006) 042305] were recently indicated to be insecure against the authenticator Trent attacks [Phys. Rev. A 75 (2007) 026301]. We present two efficient protocols by using four Pauli operations, which are secure against inner Trent attacks as well as outer Eve attacks. Finally we generalize them to multiparty quantum direction communication.

Network Entropy Based on Topology Configuration and Its Computation to Random Networks

Abstract: A definition of network entropy is presented, and as an example, the relationship between the value of network entropy of ER network model and the connect probability p as well as the total nodes N is discussed. The theoretical result and the simulation result based on the network entropy of the ER network are in agreement well with each other. The result indicated that different from the other network entropy reported before, the network entropy defined here has an obvious difference from different type of random networks or networks having different total nodes. Thus, this network entropy may portray the characters of complex networks better. It is also pointed out that, with the aid of network entropy defined, the concept of equilibrium networks and the concept of non-equilibrium networks may be introduced, and a quantitative measurement to describe the deviation to equilibrium state of a complex network is carried out.

Theoretical Prediction for Structural Stabilities and Optical Properties of SrS, SrSe and SrTe under High Pressure

Abstract: An investigation on the structural stabilities and electronic properties of SrX (X = S, Se and Te) under high pressure is conducted using the first-principles calculation based on density functional theory (DFT) with the plane wave basis set as implemented in the CASTEP code. Our results demonstrate that the sequence of the pressure-induced phase transition of the three compounds is the NaCl-type (B1) structure (Fm3m) to the CsCl-type (B2) structure (Pm3m). The phase transition and the metallization pressures are determined theoretically. The pressure effect on the optical properties is discussed. The results are compared with the previous calculations and experimental data.

Exact Solutions of Klein--Gordon Equation with Scalar and Vector Rosen--Morse-Type Potentials

Abstract: We obtain an exact analytical solution of the Klein–Gordon equation for the equal vector and scalar Rosen– Morse and Eckart potentials as well as the parity-time (PT) symmetric version of the these potentials by using the asymptotic iteration method. Although these PT symmetric potentials are non-Hermitian, the corresponding eigenvalues are real as a result of the PT symmetry.

Carbon Nanoparticles in Nematic Liquid Crystals

Abstract: Fullerene C60, C70, single-walled and multi-walled carbon nanotubes and graphene sheets are doped to nematic liquid crystal (LC) host in the same percentage. Planar samples of these mixtures are prepared and our measurements constitute an optimization basis for possible applications. Fullerene balls are found to be the best compatible material for optical aims and reorientation of LC molecules, while the carbon nanotubes experience some reorientation possibility in LC media and graphene layers are good barriers to preserve reorientation.