THE MEISSNER EFFECT IN TaSe_3

用SQUID磁强计研究了准一维导体TaSe_3的迈斯纳效应。磁化率x没有表现出任何明显的抗磁性变化，在7.2Moe到4.0Oe的低磁场范围内，磁场平行和垂直于晶体b轴。TASE_3的抗磁性很弱，且CHI值远小于-3.OX10^&lt；-3；emu/cm^3。此外，磁化率CHI在2.1K时没有表现出任何突变的迹象。单个晶须由许多纤维组成，其中一些纤维(非常细的细丝状)在2.1K以下变成超导。为什么TASE_3的迈斯纳效应在2.1K以下下降到接近零的水平？在对伦敦模型进行数值计算的基础上，讨论了这种小的抗磁性的基本来源。作为简化模型，系统地计算了半径为a的无限长圆柱体的抗磁化率X_i作为a/lambda的函数，这里lambda是伦敦穿透深度的函数。在TaSe_3中，超导区域严格限制在单晶须中沿b轴方向的极细细丝。更重要的是。这些超导细丝在0.40K以上被单独隔离在晶须中。细丝的半径远小于波长(最大为a/lambda&lt；小于等于-gt；0.30)，则磁通将均匀地穿透，从而使迈斯纳效应基本消失。我们的结果可能完全不同于大量随机取向和极大互穿的大量样品的结果。

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.