Quasiparticle and Josephson tunneling of overdoped Bi 2 Sr 2 CaCu 2 O 8¿d single crystals
Quasiparticle and Josephson tunneling of overdoped Bi 2 Sr 2 CaCu 2 O 8¿d single crystals
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过掺杂 Bi 2 Sr 2 CaCu 2 O 8 的准粒子和约瑟夫森隧道效应
DOI：
10.1103/physrevb.61.3629
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发表时间：
2000
影响因子：
3.7
通讯作者：
K. Gray
中科院分区：
文献类型：
--
作者：
L. Ozyuzer;J. Zasadzinski;C. Kendziora;K. Gray
点接触隧道技术用于检查过掺杂 Bi2Sr2CaCu2O81d ~Bi-2212 中的准粒子和约瑟夫森电流！单晶的整体 Tc 值范围从 82 K 到 62 K。超导体-绝缘体-普通金属 ~SIN！ Bi-2212 晶体和 Au 尖端之间形成隧道结，显示出高分辨率的准粒子间隙特征，包括尖锐的电导峰。可再现的超导体-绝缘体-超导体〜SIS！两片 Bi-2212 晶体之间也会产生隧道结，从而同时产生准粒子电流和约瑟夫森电流。 SIN 和 SIS 结的动态电导在质量上与最佳掺杂 Bi-2212 上的动态电导相似，但间隙值减小，例如 Tc562 K 的 D515–20 meV。间隙区域中的电导数据的拟合是使用具有 dx22y2 对称性的模型获得的，并且表明这提供了比 s 波对称性更好的拟合。 SIN 和 SIS 隧道电导在高偏压下也表现出类似于最佳和欠掺杂晶体上的凹陷和驼峰特征，表明这些是准粒子的固有属性。 SIS 数据表明，这些特征似乎是延伸至 300-400 mV 的更大频谱的一部分。已测量了 62 K 晶体上 13 个 SIS 结点的约瑟夫森电流，这些结点的电阻变化超过二十年。结果发现，最大值取决于结电阻，其方式与 Ambegaokar-Baratoff 理论一致，但 IcRn 乘积减小。
The point contact tunneling technique is used to examine quasiparticle and Josephson currents in overdoped Bi2Sr2CaCu2O81d ~Bi-2212! single crystals with bulk Tc values ranging from 82 K down to 62 K. Superconductor–insulator–normal-metal ~SIN! tunnel junctions are formed between Bi-2212 crystals and a Au tip, which display well-resolved quasiparticle gap features including sharp conductance peaks. Reproducible superconductor-insulator-superconductor ~SIS! tunnel junctions are also obtained between two pieces of the Bi-2212 crystals, resulting in simultaneous quasiparticle and Josephson currents. The dynamic conductances of both SIN and SIS junctions are qualitatively similar to those found on optimally doped Bi-2212, but with reduced gap values, e.g., D515– 20 meV for Tc562 K. Fits to the conductance data in the gap region are obtained using a model with dx22y2 symmetry, and it is shown that this provides a better fit than s-wave symmetry. Both SIN and SIS tunneling conductances also display dip and hump features at high bias voltages similar to those found on optimal and underdoped crystals, indicating that these are intrinsic properties of the quasiparticles. The SIS data indicate that these features appear to be part of a larger spectrum that extends out to 300–400 mV. The Josephson current has been measured for 13 SIS junctions on the 62 K crystals with resistances varying over two decades. It is found that the maximum value depends on junction resistance in a manner consistent with Ambegaokar-Baratoff theory, but with a reduced IcRn product.