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Simulation of Anisotropic Resistivity for Mixed-Phase Manganite La2／3Ca1／3MnO3 Thin Films

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Chinese Physics Letters 2005年第7期22卷 1749-1752页

作者：周庆莉关东仪金奎娟赵昆陈正豪吕惠宾周岳亮韩鹏杨国桢 BeijingNationalLaboratoryforCondensedMatterPhysics InstituteofPhysicsChineseAcademyofSciencesPOBox603Beijing100080

We utilize the random network model based on phase separation scenario to simulate the conductive behaviour and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 (LCMO) thin films. The simulated results agree well with our experimental data, showing a metal-to-insulator transition from a high-T paramagnetic (PM) insulating phase to a low-T ferromagnetic (FM) metallic phase in both the untilted film deposited on a (001) SrTiO3 (STO) substrate and the tilted film grown on a vicinal cut STO substrate. It is found that the resistivity of the tilted sample is higher than that of the untilted one, displaying prominent anisotropic characteristics. The studies reveal that the tilting not only decreases the conduction of the FM domains, but also increases the activation energy of the PM regions, inducing the enhancement of resistivity. All those results suggest that the intrinsic inhomogeneity in the phase separation system plays a significant role in the electrical conductivity and the resistive anisotropy is related to the structure of the crystal lattice.

关键词： PM LCMO CMR

High-Power Red Light Generation by Intra-Cavity Frequency-Doubling of a Side-Pumped Nd：YAG Laser in a LiB3O5 Crystal

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Chinese Physics Letters 2004年第10期21卷 1951-1953页

作者：孙志培李瑞宁毕勇杨晓东薄勇侯玮张瑛王桂玲赵武丽张鸿博崔大复许祖彦 LaboratoryofOpticalPhysics InstituteofPhysicsChineseAcademyofSciencesBeijing100080 GraduateSchooloftheChineseAcademyofSciences Beijing100080

We report the generation of high-power red light radiation of 11.2W in a LiB3O5(LBO) crystal with intra-cavity frequency doubling of two compact and simple side-pumped Nd:YAG laser modules under a repetition rate of 3.5kHz. The pulse width of output is about 180±20ns. The beam quality of the M2 value is 15±3 in both the directions. This excellent laser performance demonstrates that the Nd:YAG laser with LBO intracavity frequency doubling is an promising method for generating red light with high brightness.

关键词： Lithium compounds

Edge Electrostatic Fluctuation Characteristics in the Sino-United Spherical Tokamak

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Chinese Physics Letters 2004年第8期21卷 1578-1581页

作者：王文浩何也熙高喆曾立张国平解丽凤冯春华肖琼李小燕 DepartmentofEngineeringPhysics TsinghuaUniversityBeijing100084 instituteofphysics ChineseAcademyofSciencesBeijing100080

Edge plasma parameters, including electron temperature Te, density ne, plasma potential p, radial electric field Er and the corresponding fluctuations in the Sino-United Spherical Tokamak, have been systematically measured with Langmuir probe arrays. Wavenumber spectrum analyses show that edge fluctuations have a radial propagation character of the drift wave turbulence, with a characteristic radial phase velocity vphr~0.7km.s−1 in the scrape-off layer and vphr~0.9–1.4km.s−1 in the plasma edge.

关键词： Tokamak devices

Superconductivity in LiTi2O4 Prepared by Hybrid Microwave Method

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Chinese Physics Letters 2005年第1期22卷 243-245页

作者：杨立红董成宋会花郭娟伏广才 NationalLaboratoryforSuperconductivity InstituteofPhysicsChineseAcademyofSciencesBeijing100080 DepartmentofChemistry HebeiNormalUniversityShijiazhuang050091 NationalLaboratoryforSuperconductivity InstituteofPhysicsChineseAcademyofSciencesBeijing100080//DepartmentofChemistryHebeiNormalUniversityShijiazhuang050091

The well-known superconducting oxide LiTi2O4 has a structural phase transition from spinel to ramsdellite around 900 degrees C. We have successfully obtained the superconducting spinel phase and the non-superconducting ramsdellite phase of LiTi2O4 using a hybrid microwave method. The samples are characterized by x-ray powder diffraction, scanning electron microscopy, and measurements of resistivity and magnetic susceptibility. The results show that the low-temperature spinel phase is a superconductor with Tc = 13K, while the high-temperature ramsdellite phase is a semiconductor. By comparison between the crystal structures of the spinel and the ramsdellite phases, it is suggested that the geometrical frustration plays an important role in the superconductivity of the spinel LiTi2O4.

关键词：超导 LiTi2O4 混合微波法结构相位跃迁低温尖晶石

Low-Temperature Specific Heat of the Underdoped La2-xSrxCuO4 Single Crystals

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Chinese Physics Letters 2004年第2期21卷 374-377页

作者：刘志勇杨海朋鲁希锋周放闻海虎 NationalLaboratoryforSuperconductivity InstituteofPhysicsChineseAcademyofSciencesPOBox603Beijing100080

We report the low-temperature specific heat of La2−xSrxCuO4 (x = 0.063) single crystals before and after annealing in the temperature region of 2–10K and magnetic fields up to 12T. The data confirm the (H)1/2 dependence of the linear term coefficient γ predicted for d-wave paring in the Volovik theory at T = 0K. However, the data do not satisfy the proposed Simon–Lee scaling law at finite temperatures, i.e.CDOS/(T2) = f(T/(H)1/2), where f is an unknown scaling function and CDOS is the extra specific heat contributed by the nodal quasiparticles due to the Doppler effect. Possible reasons for this failure are presented.

关键词： Single crystals

A Novel Bi-wavelength Method for Accurately Measuring Gain and Noise Characteristics of an Erbium-Doped Fibre Amplifier for Multi-Channel Wavelength Division Multiplexing Transmission

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Chinese Physics Letters 2003年第10期20卷 1777-1780页

作者：刘艳格蒙红云袁树忠田建国开桂云董孝义 instituteofphysics NankaiUniversityTianjin300071 InstituteofModernOptics NankaiUniversityTianjin300071

Gain and noise figure (NF) are the most important two parameters of an erbium-doped fibre amplifier (EDFA) for a multi-channel wavelength division multiplexing (WDM) transmission system. A simple bi-wavelength method for accurate gain and NF spectrum measurement of EDFA for WDM applications is proposed. A saturating input signal, whose power equals to the sum of all the WDM signal power and whose wavelength is determined by the channel numbers, and the wavelength of the WDM input signals saturates the EDFA in a degree as the same as the WDM signals input. Meanwhile, a small power probe signal scans and measures the gain and the NF value at every wavelength of the WDM input signals. Investigative results by numerical simulation show that the gain and the NF spectra measured by this method have good agreement with the real spectra of the WDM signal input in a large total input power range. The maximum errors of the gain and the NF are less than 0.2dB and 0.16dB, respectively, for a 50-channel input case. The method is competent for the accurate gain and the NF spectrum measurement of the fibre preamplifier and the line-amplifier for WDM applications and has the advantages of simplicity, convenience and easy implement.

关键词：光传输系统光通信双波长方法增益噪音精确测量铒掺杂光纤放大器多通道波分密集传输系统

Isostructural Phase Transition of TiN under High Pressure

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Chinese Physics Letters 2005年第5期22卷 1199-1201页

作者：赵景庚杨留响余勇游淑洁禹日成李凤英陈良辰靳常青李晓东李延春刘景 instituteofphysics ChineseAcademyofSciencesBeijing100080 InstituteofHighEnergyPhysics ChineseAcademyofSciencesBeijing100039

In situ high-pressure energy dispersive x-ray diffraction experiments on polycrystalline powder TiN with NaCl-type structure have been conducted with the pressure up to 30.1GPa by using a diamond anvil cell instrument with synchrotron radiation at room temperature. The experimental results suggest that an isostructural phase transition might exist at about 7GPa as revealed by the discontinuity of V/V0 with pressure.

关键词： Sodium chloride

In-Situ Observation of Surface Phenomena During Sr（NO3）2 Crystal Growth

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Chinese Physics Letters 2003年第10期20卷 1875-1878页

作者：陈万春李宝霞李超荣 NationalMicrogravityLaboratory ChineseAcademyofSciences Beijing100080 instituteofphysics ChineseAcademyofSciencesBeijiag100080

The reflected differential interference phase contrast microscope is used to study a growing crystal surface. The surface phenomena on the {111} and {100} faces of Sr(NO3)2, such as the propagation of steps, the bunches of surface steps, the impurity stopper and the growth hillocks, have been observed during the crystal growth. It was found that: (1) The macrosteps velocity is from 0.86µm/s to 9.8×10-2µm/s on the {111} face at σ = 5.33×10-3 to 2.13×10-3. (2) If the propagating directions of the steps are in opposition, the velocity of the macrosteps will be increased after they bunched. These phenomena first provide the evidence for the existence of the mutual acceleration effect of macroscopic steps. (3) The growth hillocks include a concentric step which evidently results from successive acts of a two-dimension nucleation on surface.

关键词： Sr（NO3）2晶体晶体生长氮酸锶晶体微观结构表面现象相变固态喇曼位移

Fractal Study of Multi—branched Domains in garnet Bubble Films

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Chinese Physics Letters 2002年第5期19卷 736-738页

作者：李丹郑德娟等 StateKeyLaboratoryofMagnetism InstituteofPhysicsChineseAcademyofSciencesBeijing100080 TechnicalinstituteofphysicsandChemistry ChineseAcademyofSciencesBeijing100080

The line-measuring dimension Dline has been developed and selected to describe the curved and branched patterns of multi-branched domains (MBDs) formed by using the ``low-bias-field method'' in magnetic garnet bubble films. The definition of Dline is given. The domain pattern processing and the ``double boundary description'' of MBDs are introduced. It has been verified that the MBD patterns truly possess the characteristic of fractal structure over a certain range. The meaningful Dline seems to be a better parameter to quantitatively describe the curved and branched structure of MBDs, and can be related to the nucleation of vertical Bloch lines in their walls.

关键词： Garnets