本文研究了双轴分子磁体在耗散环境中的相干量子隧穿,作为环境的声子库抑制了相干量子隧穿,从而引起分子磁体中薛定谔猫态的退相干. 而环境内部声子之间的相互作用会导致分子磁体与热库之间退耦合，于是对退相干有一定的抑制作用. 在绝热近似和非绝热近似下，借助于约化密度矩阵计算了超Ohmo耗散中分子磁体与环境之间的纠缠度，当纠缠达到最大时，相干隧穿被完全抑制.

ENTANGLEMENT BETWEEN MOLECULAR

MAGNET AND ENVIRONMENT AND DECOHERENCE

(Received 13 October, 2003)

We study the coherent quantum tunneling in a biaxial molecular magnet with dissipation of the environment which results in the suppression of the tunneling and therefore the decoherence of Schrodinger cat states in molecular magnet. The interphonon interaction leads in an effective decoupling of the spin system from the phonon bath and therefore decreases the entanglement and decoherence. The degree of entanglement between the magnet and environment is evaluated explicitly with the help of reduced density matrix under adiabatic and nonadiabatic approximation. When the entanglement approaches maximum value the coherent tunneling is suppressed completely.

山西大学理论物理研究所， 太原 030006

本文采用 Bogliubov方法分析了光格子中玻色-爱因斯坦凝聚体的能谱,得到超流-Mott相变条件,指出光格子中BEC是一种典型的超流态,最后给出了超流速度。

( Received 11 October ,2003)

The energy spectrum of Bose-Einstein Condensation in optical lattice is analyzed by Bogliubov method. It is explicitly pointed out that such system is a typical superfluid state the velocity of superfluid is given out.

基于光纤布拉格光栅传感器的原理，研究了在液氮浸泡情况下光纤布拉格光栅应变传感器的静态传输特性。实验过程中利用悬臂梁原理和美国Micron Optics公司生产的光栅波长可调谐激光扫描法解调系统，分别测量了液氮浸泡中的悬臂梁的正应变和负应变，确定了在液氮温度下悬臂梁应变与光纤光栅波长偏移量之间的关系。为测量高温超导磁体的应变提供了新的方法。

Experiments on fiber-Bragg Grating Strain Sensor at liquid nitrogen temperature are presented. Based on the principle of the Fiber Bragg Grating Sensor the fiber-Bragg static transmission property was tested at liquid nitrogen temperature. The calibration of the fiber-Bragg grating strain sensor is given. The λ-ε curve was established.

南京大学 电子科学与工程系，南京 210093

微波近场技术是研究材料表面区域电磁性质的有效手段，结合低温技术则可将这种技术的应用拓展到更广的范围。本文报道了我们研制的低温扫描微波近场显微镜系统，它由微波近场显微镜和与之配合的可变温样品台构成，可以在液氮温度和室温之间工作。利用该系统我们详细研究了YBaCuO超导薄膜、NdSrMnO磁性薄膜在不同温度条件下的电磁性质，给出了相关实验结果。研究表明微波近场技术与低温技术的结合为电子材料和器件低温下局域电磁性质的研究提供了有力的手段。

（ Received 15 December,2003;revised manuscript received 22 December,2003）

Microwave near-field technique has been proved to be an effective tool for studying the local microwave properties of materials. In this paper, we present our low temperature scanning microwave near-field microscope system by combining the microwave near-field technique with a precisely designed low temperature sample stage. Using this system, we have investigated the local temperature dependent microwave properties of YBaCuO superconducting thin film and NdSrMnO magnetic thin film. From the experimental results, we believe that this instrument will be very helpful in the measurement of the local microwave properties of electronic materials.

本文介绍了Bi-2223/Ag高温超导带临界电流各向异性的实验测量方法及原理，指出了在不同磁场方向（与超导带面夹角）下，Bi-2223/Ag带临界电流随直流背景磁场的变化规律以及实验应注意的问题。Bi-2223/Ag带材的各向异性决定了其临界电流对垂直于带材表面的磁场非常敏感，这是该带材在高温超导磁体等强电应用方面的不利因素。

A method for measuring the anisotropic characteristic of the critical current in the Bi-2223/Ag tape is proposed in this paper. The experimental result reveals that the critical current in the Bi-2223/Ag tape varies with the magnitude of external magnetic field under different orientations of external magnetic field applied to the tape surface. The high sensitivity of the critical current in the Bi-2223/Ag tape to the perpendicular component of magnetic field on the tape, which is caused by the high anisotropy of this kind of materials, is a disadvantage for its electric power applications such as HTS magnets.

²浙江大学制冷及低温研究所 杭州 310027

³德国吉森大学应用物理研究所 德国 35392

由双向进气阀引起的直流流动是脉管制冷机在高温区如80K温度不稳定的根本原因。本文理论和实验研究了通过改变回热器流阻进行直流抑制的可行性。结果表明：适当增加回热器流阻，可以有效抑制直流，进一步改善双向进气脉管制冷机性能，实现在较高温区长时间稳定工作,为解决其存在的高温区性能不稳定提供了新的途径。

（ Received 27 November,2003）

The DC flow induced by the double-inlet in a pulse tube cooler is the main reason of temperature instability. The possibility of utilizing regenerator flow resistance to suppress DC flow is theoretically and experimentally investigated. Both results show that with a proper larger regenerator flow resistance, DC flow could be suppressed to a smaller extent. Then a long-time operation of the cooler with a stable temperature output at 80K temperature region could be carried out.

中国科学院等离子体物理研究所强磁场实验室，合肥 230031

通过控制降温的方法，我们制备了一系列不同氧含量的La_{0. 7}Ca_0.3Mn_0.92Cr_0.08O_3-δ多晶样品，并对其进行了X射线衍射谱、电阻温度关系和磁化强度以及磁电阻测量。实验发现，氧含量对电性有很特别的影响，与理想氧含量的样品不同的是，氧欠缺样品的电阻出现双峰，但是与前者一样仅有一个磁转变，这可以用样品中氧含量分布不均匀导致的相分离来解释，用这一相分离的图像我们进一步解释了文献中广泛报道的另一个有关Cr掺杂的现象：与所有锰位掺杂元素相比，Cr掺杂对铁磁转变的抑制作用最小。

EFFECTS OF OXYGEN DEFICIENCY ON THE MAGNETIZATION AND 

High Magnetic Field Laboratory , Institute of Plasma Physics,

Chinese Academy of Sciences, Hefei 230031

( Received 17 July, 2003)

华中科技大学物理系 430074

本文采用直流磁控溅射方法在（100）取向的LaAlO₃ 基片上制备了系列多层膜： La_0.67Ca_0.33MnO_3-d / La_0.67Sr_0.33MnO_3-d / La_0.67Ca_0.33MnO_3-d (LC/LS/LC)。并采用标准四探针方法对所制备样品的阻温关系进行了测量。 结果表明：在零场下,当上下两层厚度一定时，随着中间层（LS）厚度增加，多层膜的电阻率减小，金属-绝缘体转变温度(T_M-I)向高温方向移动。在中间层（LS）厚度保持一定时，随着上下两层（LC）厚度增加，其电阻率和金属-绝缘体转变温度(T_M-I)出现同样的变化规律。基于双交换理论，我们对以上结果给出了尝试性解释。

INTERACTION BETWEEN LAYERS

IN MANGANESE PEROVSKITE FILMS

( Received 20 October, 2003)

High quality La_0.67Ca_0.33MnO_3-d / La_0.67Sr_0.33MnO_3-d / La_0.67Ca_0.33MnO_3-d (LC/LS/LC) trilayered films have been achieved on LaAlO₃ (100) substrates by means of dc magnetron sputtering technique. The electrical resistivities versus temperature of the films were measured with a standard four-probe method. Results show that, for a given LC, with the increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (T_M-I) increases; for a given LS, with the increase of the thickness of LS, the zero-field resistivity (ρ) decreases and metal-insulator transition temperature (T_M-I) also increases. Based on the double-exchange (DE) mechanism, the effect of interaction between layers on the electrical transport was interpreted.

一种结构新颖、边带陡峭的

高温超导带阻滤波器