CHINESE JOURNAL OF LOW TEMPERATURE PHYSICS

Vol.26   No.2   May,  2004

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CONTENTS

Nonlinear Response of Mixed State of Superconductors¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­NING  ZHEN£­HUA,¡¡CHEN KAI-XUAN,  WANG FU-REN,  YIN DAO-LE  (89)

Preparation and Thermoelectric Properties of Ce(Ni_1-xCu_x)₂Al_{3¡­¡­¡­}LU QING-FENG,

 ¡­¡­¡­WANG YAN-WEN,  HUO DE-XUAN,  SUN PEI-JIE,  ISIKAWA YOSIKAZU, SAKURAI JUNJI  (94)

Defect Properties of the La_0.7Sr_0.3MnO₃  Epitaxial Films are Studied by a Variable

 Energy Positron Beam¡­¡­¡­¡­¡­¡­¡­¡­  JIN SHAO-WEI,  GU WEI-WEI,  ZHOU XIAN-YI,

¡­¡­¡­WU WEN-BIN,  WENG HUI-MIN,  ZHU CHANG-FEI,  YE BANG-JIAO,  HAN RONG-DIAN  (100)

Magnetoresistance analysis of Sr₂RuO₄ near Superconducting Transition

Temperature¡­¡­¡­¡­¡­¡­LIU YA-JIANG,  LUO JIAN-LIN,  CHEN ZHAO-JIA,  WANG WAN-LU  (106)

A Compact High temperature Superconducting Narrowª²band Bandpass Filter

¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ CHEN JING,  SUN LIANG,  LI SHUN-ZHOU,  HUANG JIAN-DONG,

     YIN ZHENG-CHAO,  HE AI-SHENG,  LI CHUN-GUANG,  ZHANG XUE-QIANG,  LI HONG,

  LUO SHENG,  GU CHANG-ZHI,  JIN AI-ZI,  YANG HAI-FANG,  FENG JI,  HE YU-SHENG     (111)

Experimental Investigation on dc Flow Suppression and Refrigeration

Characteristics of a High Performance Single stage GM type PTC¡­¡­¡­¡­¡­¡­

¡¡¡¡¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­ JIANG YAN-LONG,  CHEN GUO-BANG,  GAN ZHI-HUA,  G.THUMMES¡¡(119)

Influence of Low Er Doping (0.0¡Üx¡Ü0.20) on Transport Behavior in

La_0.67Sr_0.33MnO_{3¡­¡­¡­¡­¡­¡­¡­¡­}PENG ZHEN-SHENG,  LIU NING,  XU SHU-JUN,  TONG WEI  (125)

Lattice Effects on Low Fields Magnetoresistance in  Polycrystalline

La_0.7-xCe_xCa_0.3MnO_{3¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­}

¡­¡­¡­¡­ LI YAN-FEI,  ZHANG GUANG-YU,  GUI TAI-LONG,  WANG YI-JIE,  SONG WEI   (130)

The lifetime of metastate in Bose-Einstein Condensates¡­¡­¡­¡­¡­¡­¡­¡­¡­

    ¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­  ZHAO HUA,  LIANG JIU-QING  (134)

Devices and Measurement Techniques in Cryo-shock Compression Experiments

¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­SUN YUE,

  YUAN CHANG-YING,  ZHANG XIU-LU,  LIU FU-SHENG,  WU GUO-DONG,  YANG XIANG-DONG (144)

Ballistic Transport and High T_c Superconductivity¡­¡­LIU LONG-JIAN,  GAO JIE (154)

Spin Transport Property in La_0.825Sr_0.175MnO₃ Film¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­JIN KE-XIN,  CHEN CHANG-LE,  WANG YUE-LONG,

  ZHAO SHENG-GUI,  WANG YONG-CANG,  WANG SHI-LIN,  YUAN XIAO,  SONG YU-MO  (159)

Study the Effection on Double Body in Superconductors¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­

¡¡¡¡¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­¡­CHEN YU,  HUANG XIN-MIN  (163)

Differential Conductance In Differential Conductance in the Normal¡¡

Metal/d_x2-y2+id_xy Mixed Wave Superconductor Tunnel Junctions¡­ WEI JIAN-WEN  (169)

Optimization and Size Effects of NbTi Solenoids for Smes¡­¡­¡­¡­NAN HE-LI  (176)

 NONLINEAR RESPONSE OF MIXED STATE OF SUPERCONDUCTORS

NING ZHEN£­HUA ¡¡CHEN KAI-XUAN   WANG FU-REN  YIN DAO-LE

Department of Physics, Peking University, Beijing 100871

The nonlinear response functions near critical points often take the form of power law. Their relation to the homogeneous phases in both sides of transition still remains to be resolved. We show a resistive transition equation between normal and superconducting mixed states which well fits the experimental data of MgB₂ and YBCO. It also reasonably explains the puzzling amplitude-dependent peak of ac susceptibility ¦Ö¡å. The applicability of similar ¡°extended power law¡± nonlinear response for other kinds of phase transition is also discussed.

Keywords: mixed state, the amplitude of ac susceptibility, scaling, nonlinear response function

PACC:     6460, 7430F, 7460E, 3520M

PREPARATION AND THERMOELECTRIC

 PROPERTIES OF Ce(Ni_1-xCu_x)₂Al₃

LU QING-FENG¹  WANG YAN-WEN¹  HUO DE-XUAN²  SUN PEI-JIE³  ISIKAWA YOSIKAZU³  SAKURAI JUNJI³

¹College of Physics & Information Engineering, Henan Normal University,  Xinxiang 453002

²College of Material Science And Engineering, DongHua University, Shanghai  200051

³Department of Physics, Toyama University, Toyama, 930ª²8555, Japan

By partially substituting Ni with Cu, we prepared intermetallic compounds

Ce(Ni_1-xCu_x)₂Al₃(x=0.0, 0.1, 0.2, 0.3, 0.4). We determined the structure of the samples using powder X-ray diffraction, and measured the electrical resistivity ¦Ñ(T) and thermoelectric power S(T). The results reveal that the increase of unit-cell volume and the number of 3d electrons results in the weakened hybridization between 4f and conduction electrons by introducing Cu atoms into the Ni sites. With increasing the Cu concentration x, the Kondo temperature T_K decreases, and the system tends to form heavy electronic compound.

Keywords: Intermetallic compounds, thermoelectric power, Electrical resistivity, Powder X-ray diffraction, Ce(Ni_1-xCu_x)₂Al₃, heavy electronic compound

PACC: 7127£¬ 7128£¬ 7215J

DEFECT PROPERTIES OF THE La_0.7Sr_0.3MnO₃

EPITAXIAL FILMS ARE STUDIED BY

A VARIABLE ENERGY POSITRON BEAM

JIN SHAO-WEI  GU WEI-WEI  ZHOU XIAN-YI WU WEN-BIN

WENG HUI-MIN  ZHU CHANG-FEI  YE BANG-JIAO  HAN RONG-DIAN

¹Department of Modern Physics, University of Science and Technology of China, Hefei 230027

²Structure Research Laboratory, University of Science and Technology of China, Hefei 230026

³Department of Materials Science and Engineering, University of Science

and Technology of China, Hefei 230026

(Received  15 October, 2003)

By using a variable energy positron beam system, the linear S parameter as a function of implantation positron energy was measured on the epitaxial La_0.7Sr_0.3MnO₃ thinfilms from different deposition oxygen pressures. It is found that the relationship between the S parameters of the epitaxial La_0.7Sr_0.3MnO₃ films and oxygen pressures is not monotonous. This relationship is related to the actions of the deposition oxygen pressure. For the La_0.7Sr_0.3MnO₃ film was prepared by the high growth oxygen pressure, the increase of the vacancy concentration is caused from the large collision faction of the deposition atom and oxygen atom. In contrast, for the film prepared by the low growth oxygen pressure, the increase of the vacancy concentration is caused from the oxygen atom deficiency during the film growth and resulted in the oxygen vacancies and the related defect complexes.

Keywords: defect properties, epitaxial films, positron annihilation

PACC:     7570, 7870b

MAGNETORESISTANCE ANALYSIS

OF Sr₂RuO₄  NEAR SUPERCONDUCTING

TRANSITION TEMPERATURE

LIU YA-JIANG  LUO JIAN-LIN  CHEN ZHAO-JIA  WANG WAN-LU

¹Department of Applied Physics, Chongqing University, Chongqing 400044

²Institute of Physics, Chinese Academy of Sciences, Beijing 100080

£¨Received 15 October ,2003£©

We report a detailed study of the c axis magnetoresistance near superconducting transition temperature in Sr₂RuO₄, the layered perovskite superconductor which does not contain copper. By the analysis of the normal state magnetoresistance we have obtained the in plane mean free path. A large positive magnetoresistance near T_c  has been observed, which is originated from superconducting fluctuations. The fluctuation-enhanced magnetoconductivity very close to T_c shows well agreement with Aslamasov-Larkin(AL) prediction for a 2-D superconductor, and the coherence lengths of Sr₂RuO₄, have been deduced from fluctuation magnetoresistance analysis at 1.5K.

Keywords: superconducting fluctuation, magnetoresistance

PACC:     0540, 7530V, 4210M

A COMPACT HIGH-TEMPERATURE

SUPERCONDUCTING NARROW-BAND

BANDPASS FILTER

CHEN JING   SUN LIANG   LI SHUN-ZHOU   HUANG JIAN-DONG

YIN ZHENG-CHAO   HE AI-SHENG   LI CHUN-GUANG   ZHANG XUE-QIANG   LI HONG

LUO SHENG   GU CHANG-ZHI   JIN AI-ZI   YANG HAI-FANG   FENG JI   HE YU-SHENG

¹Institute of Physics, Chinese Academy of Sciences, Beijing  100080

²Department of Physics, University of Science and Tecnology, Beijing  100083

³Institute of Acoustics, Chinese Academy of Sciences, Beijing  100080

£¨Received 15 October, 2003£©

A compact high-temperature superconducting narrow-band bandpass filter was fabricated. The filter was designed to have a center frequency 1725MHz, and fabricated using double-side-coated YBCO thin film on a 0.5mm-thick lanthanum aluminate substrate (¦År¡Ö24). An encouraging performance has been achieved. The measured responses of the filter showed a insertion loss of <0.3dB, a return loss of <-16dB in the filter passband£¬ a fractional bandwidth of <9¡ë, and a steepness better than 9dB/MHz. The deviation of the central frequency is smaller than 0.05%. A pair of transmission zeros located at both sides of the passband were introduced with a special technique in designing, which has greatly improved the frequency response characteristics of the filter and can be used as a helpful new method in future compact bandpass filter design.

Keywords: HTS, microwave applications£¬ bandpass filter

PACC:     7470V, 7870G, 4280C

EXPERIMENTAL INVESTIGATION ON

DC FLOW SUPPRESSION AND REFRIGERATION

CHARACTERISTICS OF A HIGH-PERFORMANCE

SINGLE-STAGE GM-TYPE PTC

JIANG YAN-LONG   CHEN GUO-BANG   GAN ZHI-HUA   G.THUMMES

¹Department of Man-Machine and Environment Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing  210016

²Cryogenics laboratory, Zhejiang University, Hangzhou 310027

³Institute of Applied Physics, University of Giessen 35392, Germany

(Received  5 August, 2003; revised manuscript received  19  November, 2003)

Experimental investigation on DC flow suppression and refrigeration characteristics of a high-performance single-stage GM-type pulse tube cooler has been undertaken in this paper. The influence of DC flow induced by the introduction of double-inlet on the refrigeration performance of the cooler is experimentally examined. Two parallel-placed needle valves with opposite flow direction called as double-valved configuration, instead of conventional single-valved configuration as the double-inlet is successfully used in this experiment to reduce the DC flow. Besides, the performance of the cooler with various regenerator matrices and supply power of compressors has been extensively investigated under different operation modes. Operating under double-inlet mode, 18.4K and 14.7K minimum temperature has been reached driven by RW2 and CP4000 compressor respectively, and 11.5W and 29.5W cooling power at 30K have been obtained as well.

Keywords: High-performance, pulse tube cooler, DC flow

PACC:     0720

INFLUENCE OF LOW Er DOPING (0.0¡Üx¡Ü0.20)

ON TRANSPORT BEHAVIOR IN La_0.67Sr_0.33MnO₃

¡¡

PENG ZHEN-SHENG  LIU NING   XU SHU-JUN   TONG WEI

¹Department of physics, Suzhou Advanced Normal College, Suzhou  234000

²Structure Research Lab, University of Science and Technology of China, Hefei  230026

(Received 11 December, 2003)

By measuring M-T curves and ¦Ñ-T  curves, we have studied the influence of low Er doping (0.0¡Üx¡Ü0.20) on magnetic and electric properties of La_0.67Sr_0.33MnO₃. We found that the substitution for La site by a smaller rare-earth ion Er reduces both Curie temperature and magnetization, which is regarded as the result from that the decreasing of ion radius at A site causes larger distortion of Mn-O-Mn bonds and weakens double-exchange interaction. At the same time, local magnetic moment of rare-earth ion affects physical properties of the system. At FM phase, the system is dominated by single magneton scattering and shows metallic conduction which can be fitted by the formula ¦Ñ=¦Ñ₀+AT²;  While in the low temperature the resistivity behavior deviates from T2 relation, which can be understood in terms of the significant contribution from the scattering of local magnetic moments of Er ions on carriers. The two transport properties of small polaron in PM phase and single magneton in FM phase coexist at the temperature region of phase transition.

Keywords: CMR material, single magneton, small polaron

PACC:     7530V, 7500

LATTICE EFFECTS ON LOW

FIELDS MAGNETORESISTANCE IN

POLYCRYSTALLINE La_0.7-xCe_xCa_0.3MnO₃

LI YAN-FEI   ZHANG GUANG-YU   GUI TAI-LONG   WANG YI-JIE   SONG WEI

Applied Science Institute,  Harbin University of Science & Technology,  Harbin 150080

£¨Received 10 October, 2003£©

The manganite polycrystalline samples La_0.7-xCe_xCa_0.3MnO₃ (x=0, 0.05, 0.10, 0.20) were prepared by the solid-state reaction technique. The electrical resistance (R) and low fields magnetoresistance (MR) have been measured in the temperature region from 77K to 300K in applied fields from zero to 0.25 Tesla. The element substitution of Ce for La and the doping concentration dependence of R and MR were studied. It is found that the giant magnetoresistance (GMR) in the Ce doping samples does not change obviously, while the characteristic temperature T_P, at which the peak of MR appears, descend from that in La_0.7Ca_0.3MnO₃. The notion that decreasing <r_A> results decrease in the Mn-O-Mn bond angle as well as T_c avail to understand these experimental results.

Keywords: magnetoresistance, manganites

PACC:     7590

THE LIFETIME OF METASTATE

IN BOSE-EINSTEIN CONDENSATES

ZHAO HUA   LIANG JIU-QING

Institute of Theoretical Physics, Shanxi University, Taiyuan, Shanxi  030006

£¨Received 13 October, 2003£©

The exact quantum phase model is derived with the help of a mesoscopic spin modeled from weakly linked two-component Bose-Einstein Condensates. It is shown that the  metastate exist only in some parameter region. The decay of the metastable-state via quantum tunneling is studied and the life time is found analytically by instanton method.

Keywords: exact quantum phase model, instanton method£¬ metastable-state

PACC:     3000, 7340G

DEVICES AND MEASUREMENT TECHNIQUES

IN CRYO-SHOCK COMPRESSION EXPERIMENTS

SUN YUE   YUAN CHANG-YING   ZHANG XIU-LU   LIU FU-SHENG   WU GUO-DONG   YANG XIANG-DONG

¹Inst. of High Temp.& High Pres. Phys., Sichuan University, Chengdu  610065

²Inst. of Fluid Phys.,CAEP, Mianyang, Sichuan, P.R.China  621900

³Institute of high pressure and high temperature, Southwest Traffic University, Chengdu  610031

£¨ Received 17 October, 2003;  revised manuscript received 12 November, 2003£©

An improved cryo-target system, including a cryo-target body, a sub-cooledª²gas generator with a controller, a bubble-boil state monitor and anodized Al shock coaxial detectors, has been successfully introduced into cryo-shock compression experiments based on a two-stage light gas gun. Two or three special parts of these apparatuses are discussed and some corresponding experimental methods are discussed in detail. Furthermore, to verify the system, a monomer sample of liquid CO₂(LCO₂) was shock-compressed to the pressure up to the range 22¡«60GPa (220¡«600kbar). The results obtained from this experiments are compared with the previous data. As the final shocked results shown, the improved cryo-target system is more reasonable and simple in its framework, of easier operation, multifunction and low cost. Those data obtained from the renewed system displayed more accurate, better repeatability and consistency. The conclusion hence is that the set of apparatus may be easily used to all simple substances shock compression experiments within the temperature range of 300¡«77K, and even to liquid helium(4K) or hydrogen(20K).

Keywords£ºshock compression, cryo-target, two-stage light gas gun, photoelectric monitor, anodization, shockwave velocity detector

PACC:    0620D, 0620H

BALLISTIC TRANSPORT AND

HIGH -Tc SUPERCONDUCTIVITY

LIU LONG-JIAN^1,2   GAO JIE²

¹Laboratory Center of Physics, Xi Hua University, Chengdu  610039

²Department of Physics, Sichuan University, Chengdu  610065

(Received 15 July, 2003)

The concept of ballistic transport is uniquely introduced in this paper. Behavior of carriers in the state of ballistic transport explains uniformly the anisotropies and the anomalous temperature behaviors of resistivity and the Hall constant of high temperature superconductors in normal state. This deduces the anisotropy and the anomalous temperature behavior of thermoelectric power in different directions as well. And also, this paper discusses the transforming process from normal state to superconducting state. A qualitative formula about the relationship between Tc and some physical parameters of high temperature superconductors is given.

Keywords£ºballistic transport, high Tc superconductivity, normal state, transport property

PACC:     7425, 7472

SPIN TRANSPORT PROPERTY

IN La_0.825Sr_0.175MnO₃ FILM

JIN KE-XIN¹  CHEN CHANG-LE¹  WANG YUE-LONG¹

ZHAO SHENG-GUI¹   WANG YONG-CANG¹   WANG SHI-LIN¹   YUAN XIAO²  SONG YU-MO¹

¹Department of applied physics,Northwestern Polytechnical University, Xi¡äan  710072

²State Key Lab of Laser Technology,Hua Zhong University of Sience and Technology, Wu han  430074

£¨Received  30  October, 2003£©

Doped manganese oxide, La_0.825Sr_0.175MnO₃(LSMO), with perovskite structure was prepared by traditional solid reaction method. The thin film with thickness of 50nm was deposited using a RF magnetron sputtering method on LaAlO₃ Substrate. The X-ray diffraction of the film and the block indicated that LSMO film and LaAlO₃ substrate had the same perovskite structure. The transport property of the film was obviously changed by optical and magnetic fields. And it was thought to be the external fields which had influenced on the system of spin system.

Keywords: doped manganese oxides, photo-induced effect, spin transport property, double exchange effect

PACC:     7360, 7865

STUDY THE EFFECTION ON DOUBLE

BODY IN SUPERCONDUCTORS

CHEN YU   HUANG XIN-MIN

Department of Chemistry Shaanxi Techonology University, Shaanxi Hanzhong  723000

£¨Received 15 October ,2003£©

The all elements effect Hanmilton function and quantum mechamics equation have been established based on the characteristic structure of high temperature superconductor material. We adopt the principal layer structure which is a commonly accepted. After simplification, the time content perturbation method has been used to sidestep the divergent difficult in common perturbation menthod. Some meaningful results are obtained.

Keywords: Characteristic structure of superconductor material, all elements effect Hamilton function, time content perturbation

PACC:    7420, 7100

DIFFERENTIAL CONDUCTANCE IN

THE NORMAL METAL/d_x2-y2+id_xy MIXED

WAVE SUPERCONDUCTOR TUNNEL JUNCTIONS

WEI JIAN-WEN

Department of Physics, Huaiyin Teachers College, Jiangsu Huaian  223001

(Received 5 September, 2003; revised manuscript received 29 September 2003)

Using Bogoliubov-de Gennes (BdG) equation and Blonder-Tinkham-Klapwijk (BTK) theory, we calculate the quasiparticle transport coefficients and the differential conductance in the normal metal/d_x2-y2+id_xy