Preparation of Ultrathin and Granular Superconducting Films, and Studies on Electronic Properties at Very Low Temperatures

超薄粒状超导薄膜的制备及极低温电子性能研究

基本信息

批准号：
06452058
负责人：
OKUMA Satoshi
金额：
$ 4.86万
依托单位：
TOKYO INSTITUTE OF TECHNOLOGY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06452058/
关键词：
2D superconductors Ultrathin films Granular films S-I transition Hall effect Bose-glass phase Vortex-glass phase Mixed state 2次元超伝導体、超薄膜、スケーリング則渦糸電子局在

项目摘要

We have constructed a cryogenic evaporator which allows us to fabricate clean and ultrathin (or granular) films of indium, which could not be obtained by conventional deposition at room temperatures, and to measure them in situ below 0.5 K under magnetic fields up to 11 T.Using these superconducting films, we have studied effects of quantum fluctuations as well as thermal fluctuations on the phase transition.1. We have measured the Hall resistance as well as the longitudinal resistance for disordered thin indium films and found the unusual insulating phase where R_<xx> diverges but R_<xy> is small or zero at T*0. From the result, we have proposed a possibility that the insulating phase corresponds to the Bose-glass insulator where the phase fluctuates quantum-mechanically and Cooper pairs are localized. In order to make a definitive statement on Bose-glass insulator, further experiments at even lower temperatures (-10mK) are necessary.2. Nonlinear resistivities (I-V characteristics) for indium films have been studied in various magnetic fields B.(1) The Meissner phase (B=0) : The I-V characteristics for thin films (<14nm) are well described by the two-dimensional (2D) KT theory. As the films become thicker, I-V curves are altered and are explained in terms of the recent theory considering 3D vortex loops. Thus, the dimensionality crossover for vortices from 2D to 3D is clearly observed. (2) The mixed state (B*0) : The I-V curves for thick films are analyzed according to the 3D vortex-glass theory. We have found the field-independent critical exponents and the scaling functions, which are similar to those obtained in high T_C superconductors, indicating that the VG transition is universal in type II superconductors. Finite-size effects are visible for thinner films (2D dirty superconductor) as well as for thick films with larger grain sizes (3D Josephson network), which are also consistent with the VG picture.

我们已经构建了一个低温蒸发器，该蒸发剂使我们能够制造清洁和超薄（或颗粒状）粘膜的膜，无法通过常规沉积在室温下通过常规沉积来获得，并在磁场下以低于11 t的磁场进行测量。使用这些超导膜，我们研究了量子波动的影响以及对相变的热波动。1。我们已经测量了大厅的电阻以及无序薄膜膜的纵向电阻，并发现了不寻常的绝缘阶段，其中r_ <xx>分歧，但r_ <xy>在t*0时很小或零。从结果来看，我们提出了绝缘阶段对应于玻色玻璃绝缘体的可能性，该阶段是机械量子的波动，库珀对被定位。为了对Bose-Glass绝缘子做出明确的陈述，需要在较低温度（-10MK）上进行进一步的实验。2。在各种磁场B中都研究了依赖膜的非线性电阻率（I-V特性）B。（1）二维膜（<14nm）的Meissner阶段（B = 0）：二维（2d）很好地描述）KT理论。随着膜变得越来越厚，I-V曲线会改变，并用最近考虑3D涡流环的最新理论来解释。因此，清楚地观察到了从2D到3D的涡流的尺寸交叉。（2）混合状态（B*0）：根据3D涡流理论分析厚膜的I-V曲线。我们发现了与磁场无关的临界指数和缩放函数，与高T_C超导体中获得的尺度函数相似，表明VG转变在II型超导体中是通用的。对于较薄的薄膜（2D肮脏的超导体）以及具有较大谷物尺寸的厚膜（3D Josephson网络），有限尺寸的效果可见，这也与VG图片一致。