THE MEISSNER EFFECT IN TaSe_3

用SQUID磁强计研究了准一维导体TaSe_3的Meissner效应。磁化率x在7.2 MoE ~ 4.0 Oe的低磁场范围内与晶体b轴平行和垂直时，抗磁性没有任何显著变化，抗磁性非常弱，chi值远小于-3.0X10 ^<-3>emu/cm ^3。此外，在2.1K时，磁化率χ没有任何突变的迹象.单个晶须由许多纤维组成，其中一些纤维（很细的类超导体）在2.1K以下变为超导。TaSe_3的电阻率在2.1K以下下降到接近零。为什么TaSe_3中的迈斯纳效应受到很强的抑制？本文在数值计算的基础上讨论了这种小抗磁性的基本来源，作为一个简化模型，系统地计算了半径为a的无限长圆柱体的抗磁化率chi与a/λ的关系，λ为伦敦穿透深度。在TaSe_3中，超导区严格限制在单个晶须中沿b轴沿着极细的丝。此外。这些超导细丝在晶须中在高于0.40K时被单独隔离。当细丝的半径远小于λ（最大为a/λ <less than or equal>0.30）时，磁通量将均匀地穿透，从而使迈斯纳效应基本消失，我们的实验结果给出了单根晶须的本征材料性质。我们的结果可能完全不同于大量的块状试样，随机取向，大大贯穿。

THE MEISSNER EFFECT IN TaSe_3 The Meissner effect of the quasi-one-dimensional conductor TaSe_3 is studied using a SQUID magnetometer. Susceptibility x does not show any significant variation of diamagnetism, with magnetic fields parallel and perpendicular to crystalline b-axis over a low magnetic field range of 7.2 mOe to 4.0 Oe. The diamagnetism is quite weak and the value of chi is much less than -3.OX10^<-3> emu/cm^3. Furthermore, thd susceptibility chi does not exhibit any indication of an abrupt change at 2.1 K. A single whisker consists of many fibers where some fibers (very thin filament-like) become superconducting below 2.1 K.Resistivity of TaSe_3 drops near zero below 2.1 K. Why is the Meissner effect suppressed quite strongly in TaSe_3 ? A basic origin of this small diamagnetism is discussed on the basis of numerical computer calculations for the London model.As a simplified model, the diamagnetic susceptibility chi for a infinite cylinder having radius, a , is calculated systematically as a function of a/lambda, here lambda is the London penetration depth. In TaSe_3, the superconducting region is strictly restricted to extremely thin filaments along the b-axis in the single whisker. Furthermore. these superconducting filaments are individually isolated above 0.40 K in the whisker. The radii of the filaments are much less than lambda ( at most a/lambda <less than or equal>0.30 ), then, the magnetic flux will penetrate uniformly.Consequently the Meissner effect is substantially smeared out.It should be noted that our experimental results give the single whisker's intrinsic material property. Our results could totally differ from that of the large amount of massive specimens which are randomly oriented and are greatly interpenetrating.