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Dissipation-induced Superconducting Transition in one-dimensional arrays of Josephson Junction

约瑟夫森结一维阵列中耗散引起的超导转变

基本信息

批准号：
12640336
负责人：
OOTUKA Youiti
金额：
$ 2.3万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

The superconductor-to-insulator (SI) transition in small Josephson junction arrays is a typical example of the quantum phase transition. The aim of this research was to clarify the role of dissipation in the transition in one-dimensional array of Josephson junctions. In order to investigate the effects of quantum fluctuations and dissipation in Josephson junction array, we have fabricated one-dimensional arrays of Al small Josephson junctions, each of which was shunted by Cr shunt resistance, and measured the I/V characteristics at low temperatures. Our conclusions are as follows.1. We have observed the SI transition in 1d arrays of Josephson junction caused by dissipation as well as by quantum fluctuation. Namely, arrays with large E_J/E_C or with small R_S showed the Josephson-like I-V characteristics and the zero-bias resistance decreased at the lowest temperature. On the other hand, those with small E_J/E_C and large R_S showed the Coulomb blockade in the I-V characteristics and the resistance increased. Here, E_J, E_C, and R_S are the Josephson energy, the single electron charging energy and the shunting resistance, respectively.2. Based on the observation, we have determined the phase diagram of the system at T= 0 K in the parameter space of E_J/E_C and R_S.3. The S-I transition takes place at R_S nearly equals to the quantum resistance R_Q when E_J/E_C <<1, which supports the theories of dissipative phase transition in this system.4. The critical value of E_J/E_C for the case R_Q/R_S =0 was much smaller than the theoretical prediction, for which we have no definite answer yet.5. We have also observed the insulators-to-superconductor transition when we increase the width of the array from one-dimensional chain to two-dimensional one.

小约瑟夫森结阵列中的超导体-绝缘体（SI）相变是量子相变的一个典型例子。本研究的目的是阐明耗散在一维约瑟夫森结阵列中的转变中的作用。为了研究量子涨落和耗散对约瑟夫森结阵列的影响，我们制作了一维Al小约瑟夫森结阵列，每个结都被Cr分流电阻分流，并测量了低温下的I/V特性。我们的结论如下：1.在一维约瑟夫森结阵列中观察到了由耗散和量子涨落引起的SI跃迁。即在最低温度下，具有较大EJ/E_C或较小R_S的阵列表现出类约瑟夫森I-V特性，零偏电阻减小。而小EJ/E C、大R S的样品，I-V特性表现为库仑阻塞，电阻增大。其中E_J、E_C和R_S分别是约瑟夫森能量、单电子充电能量和分流电阻.在此基础上，我们在E_J/E_C和R_S参数空间中确定了T= 0 K时的相图。当E_J/E_C <<1时，S-I相变发生在R_S近似等于量子电阻R_Q处，支持了该系统的耗散相变理论.当R_Q/R_S =0时，E_J/E_C的临界值远小于理论预测值，对此我们还没有明确的答案.我们还观察到当我们将一维链的宽度增加到二维链的宽度时，绝缘体到超导体的转变。