In the last 30 days

• Open/close An X-Ray Diffraction and Thermogravimetric Study of Layered Perovskite Y_1−xBi_xBaCo₄O₇

  Zhang Ya-Mei (张亚梅) et al 2011 Chinese Phys. Lett. 28 128202 Tag this article

  Article References Full text PDF (845 KB)

  Layer-structured oxides Y _1−xBi _xBaCo ₄O ₇ (0.00 ≤ x ≤ 0.05) were successfully synthesized and their structural and oxygen absorption properties were investigated by x-ray diffraction and thermogravimetry. Though Bi solubility was limited to about 5%, corresponding to Y _0.95Bi _0.05BaCo ₄O ₇, it is found that the structure and oxygen absorption properties of Y _1−xBi _xBaCo ₄O ₇ are affected significantly as the Bi content x increases. Rietveld refinement results show that Y _1−xBi _xBaCo ₄O ₇ ( x ≤ 0.05) is single phase with a hexagonal crystal structure (space group P6 ₃zmc). Unit cell parameters and volume are changed and CoO ₄ tetrahedra are distorted along the c-axis in Bi doped YBaCo ₄O ₇. The TG results show that Y _1−xBi _xBaCo ₄O ₇ undergoes two oxygen absorption processes in oxygen from room temperature to 1000°C and the maximum mass increase of the doped samples is less than that of YBaCo ₄O ₇. Bi doping effects on the structure and oxygen absorption properties are discussed on the basis of average radius and disorder of the Y site, the valence of Bi and the oxygen activation energy.

• Open/close Control of Fractal Erosion of Safe Basins in a Holmes—Duffing System via Delayed Position Feedback

  Shang Hui-Lin (尚慧琳) 2011 Chinese Phys. Lett. 28 010502 Tag this article

  Article References Full text PDF (513 KB)

  A linear delayed position feedback control is applied to control the erosion of safe basins in a Holmes-Duffing system. The conditions of fractal erosion of the safe basin of the controlled system on the basis that the range of time delay leading to good control is obtained by the Melnikov method. It is found that the increasing time delay can reduce the basin erosion under a weak and positive feedback gain. Then the evolutions of safe basins with time delay are presented in detail by the fourth Runge-Kutta and Monte-Carlo methods, which shows that the safe basin of the controlled Holmes-Duffing system can be expanded, and its fractal can be reduced by the increasing time delay. These results suggest that delayed position feedbacks can be used as a good approach to control the erosion of safe basins.

• Open/close Three-Dimensional Thermal Analysis of 18-Core Photonic Crystal Fiber Lasers

  Zheng Yi-Bo (郑一博) et al 2012 Chinese Phys. Lett. 29 024203 Tag this article

  Article References Full text PDF (847 KB)

  The three-dimensional thermal properties of 18-core photonic crystal fiber lasers operated under natural convection are investigated. The temperature sensing technique based on a fiber Bragg grating sensor array is proposed to measure the longitudinal temperature distribution of a 1.6-m-long ytterbium-doped 18-core photonic crystal fiber. The results show that the temperature decreases from the pump end to the launch end exponentially. Moreover, the radial temperature distribution of the fiber end is investigated by using the full-vector finite-element method. The numerical results match well with the experimental data and the coating temperature reaches 422.7K, approaching the critical value of polymer cladding, when the pumping power is 40 W. Therefore the fiber end cooling is necessary to achieve power scaling. Compared with natural convection methods, the copper cooling scheme is found to be an effective method to reduce the fiber temperature.

• Open/close Atomic Force Microscopy of Surface Reconstructed SrTiO₃ Vicinal Substrates for Epitaxial Growth of YBa₂Cu₃O_7-δ Thin Films

  Hu Wen-fei et al 1999 Chinese Phys. Lett. 16 853 Tag this article

  Article References Full text PDF (492 KB)

  SrTiO ₃(001) vicinal substrates of miscut 1°, 3°, and 6° toward the (001) plane were annealed at 800-1000° C in pure flowing O ₂ for 6 h and examined by atomic force microscopy. The high temperature annealed vicinal SiTiO ₃(001) displayed arrays of straight steps and smooth terraces. The step heights vary from about 2 to 6 unit cell depending on the annealing temperatures. At 1000° C, step bunching becomes obvious. The height steps of 1 unit cell are difficult to be observed by our atomic force microscopy. The YBa ₂Cu ₃O _7-δ thin film grows epitaxially on the step-terrace surface with c-axis orientation by magnetron sputtering in the two-dimensional island mode. Prospect of step-flow growth is being discussed.

• Open/close New Mechanical Feature of Two-Solitary Wave to the KdV Equation

  Dai Zheng-De (戴正德) et al 2012 Chinese Phys. Lett. 29 040201 Tag this article

  Article References Full text PDF (815 KB)

  New breather solitary solution and two-solitary solutions depending on constant equilibrium solution to the Korteweg de Vries equation are obtained by using an extended homoclinic test approach. A new mechanical feature of a two-solitary wave, namely, dependence of propagation direction and shape on position of equilibrium point, is investigated.

• Open/close Interface-Induced High-Temperature Superconductivity in Single Unit-Cell FeSe Films on SrTiO₃

  Wang Qing-Yan (王庆艳) et al 2012 Chinese Phys. Lett. 29 037402 Tag this article

  Article References Full text PDF (868 KB)

  We report high transition temperature superconductivity in one unit-cell (UC) thick FeSe films grown on a Se-etched SrTiO ₃ (001) substrate by molecular beam epitaxy (MBE). A superconducting gap as large as 20 meV and the magnetic field induced vortex state revealed by in situ scanning tunneling microscopy (STM) suggest that the superconductivity of the 1 UC FeSe films could occur around 77 K. The control transport measurement shows that the onset superconductivity temperature is well above 50 K. Our work not only demonstrates a powerful way for finding new superconductors and for raising T _C, but also provides a well-defined platform for systematic studies of the mechanism of unconventional superconductivity by using different superconducting materials and substrates.

• Open/close A Novel Large Moment Antiferromagnetic Order in K_0.8Fe_1.6Se₂ Superconductor

  Bao Wei (鲍威) et al 2011 Chinese Phys. Lett. 28 086104 Tag this article

  Article References Full text PDF (1.03 MB)

  The discovery of cuprate high T _C superconductors has inspired the search for unconventional superconductors in magnetic materials. A successful recipe has been to suppress long-range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point. We report an exception to this rule in the recently discovered potassium iron selenide. The superconducting composition is identified as the iron vacancy ordered K _0.83(2)Fe _1.64(1)Se ₂ with T _C above 30 K. A novel large moment 3.31 μ _B/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature T _N ≈ 559 K for a bulk superconductor. Staggeringly polarized electronic density of states is thus suspected, which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.

• Open/close Properties of All-Solid Square-Lattice Photonic Bandgap Fibres

  Shi Qing et al 2007 Chinese Phys. Lett. 24 2259 Tag this article

  Article References Full text PDF (297 KB)

  Properties of all-solid square-lattice photonic bandgap fibres are studied for the first time to the best of our knowledge. Using the plane-wave expansion method and finite element method, we investigate the mode, effective area, confinement loss and dispersion of such fibres. The simulation results demonstrate that the proposed effective mode area of all-solid square-lattice photonic bandgap fibres is 1.25 times larger than triangular-lattice ones and the confinement loss of the fibres is no more than 0.1 dB/m within the bandgap.

• Open/close Entanglement Dynamics of Arbitrary Two-Qubit Pure States under Amplitude and Phase Damping Channels

  Jiang Feng-Jian (蒋峰建) et al 2011 Chinese Phys. Lett. 28 020308 Tag this article

  Article References Full text PDF (1.36 MB)

  Analytic results are presented for the entanglement evolution for arbitrary two-qubit pure state under amplitude damping and particularly phase damping channel. The disentanglement time and the relationship between it and the form of initial state are given explicitly. The lower bounds of disentanglement time are obtained and shown to be the monotone functions of initial concurrence.

• Open/close Superconductivity at 55 K in Iron-Based F-Doped Layered Quaternary Compound Sm[O_1-xF_x] FeAs

  Ren Zhi-An et al 2008 Chinese Phys. Lett. 25 2215 Tag this article

  Article References Full text PDF (128 KB)

  We report the superconductivity in iron-based oxyarsenide Sm[O _{1- x}F _x ]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.