Nonergodic metallic and insulating phases of Josephson junction chains
Nonergodic metallic and insulating phases of Josephson junction chains
复制标题
约瑟夫森连接链的非遍历金属相和绝缘相
DOI：
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发表时间：
2015
影响因子：
11.1
通讯作者：
B. Altshuler
中科院分区：
文献类型：
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作者：
M. Pino;L. Ioffe;B. Altshuler
传统的平衡统计物理学旨在描述具有多个自由度的动力学系统，其关键依赖于均分假设：在演化足够长的时间后，找到具有相同能量的状态的系统的概率是相等的。因此，时间平均被假定为等同于能量壳层上的平均--著名的遍历假设。在这项研究中，我们表明，这一假设是不正确的一个大类的量子多体模型，可以在实验室中实现。这些模型预计将显示一种新的行为类型，我们称之为坏金属，它既不是多体绝缘体，也不是传统的导体。严格地说，传统统计物理学的定律，基于均分假设[吉布斯J W（1902）统计力学基本原理，特别是参考热力学的理性基础]和遍历假设[玻尔兹曼L（1964）气体理论讲座]，只适用于存在热浴的情况。直到最近，这种限制被认为对真实的物理系统并不重要，因为与浴的弱耦合被认为是足够的。然而，直到最近，当量子气体和固态相干量子器件的进展允许人们研究与浴的耦合大大减少的系统时，这种信念才得到认真的检验。为了恰当地描述这样的系统，人们应该重新审视统计力学的基础。我们研究这个一般性的问题的情况下，可以在实验室中实现的约瑟夫森结链，并表明，它显示了一种新的高温非遍历相有限电阻。随着温度的进一步升高，系统经历了一个过渡到完全局域化的状态，其特征在于无限的电阻和指数长的松弛。
Significance Conventional equilibrium statistical physics that aims to describe dynamical systems with many degrees of freedom relies crucially on the equipartition postulate: After evolving for a sufficiently long time, the probabilities to find the system in states with the same energy are equal. Time averaging is thus assumed to be equivalent to the averaging over the energy shell—the famous ergodic hypothesis. In this study we show that this hypothesis is not correct for a large class of quantum many-body models that can be implemented in the laboratory. These models are predicted to show a novel type of behavior that we name bad metal, which is neither a many-body insulator nor a conventional conductor. Strictly speaking, the laws of the conventional statistical physics, based on the equipartition postulate [Gibbs J W (1902) Elementary Principles in Statistical Mechanics, developed with especial reference to the rational foundation of thermodynamics] and ergodicity hypothesis [Boltzmann L (1964) Lectures on Gas Theory], apply only in the presence of a heat bath. Until recently this restriction was believed to be not important for real physical systems because a weak coupling to the bath was assumed to be sufficient. However, this belief was not examined seriously until recently when the progress in both quantum gases and solid-state coherent quantum devices allowed one to study the systems with dramatically reduced coupling to the bath. To describe such systems properly one should revisit the very foundations of statistical mechanics. We examine this general problem for the case of the Josephson junction chain that can be implemented in the laboratory and show that it displays a novel high-temperature nonergodic phase with finite resistance. With further increase of the temperature the system undergoes a transition to the fully localized state characterized by infinite resistance and exponentially long relaxation.