Low energy electrodynamics of strongly interacting disordered systems: quantum phase transitions and many-body localization

非技术性描述：我们对物理系统的大部分了解都来自于它们对特征频率扰动的响应，这一点并不夸张。例如，小提琴琴弦的基本音调取决于琴弦的长度、张力和厚度。从小提琴的声音到原子的能量都是如此。不幸的是，许多固体材料的固有频率范围落在一个频谱范围内，这一直是非常难以技术访问，直到最近。该项目利用最近在太赫兹和微波光谱学方面的巨大技术进步来表征无序固体的自然频率尺度。像超导体这样的材料系统，可以在没有电阻和各种绝缘状态的情况下导电，正在研究之中。本文进行的调查提供了必要的信息，开发具有重要技术意义的新材料。这些技术发展与教育和外联方面的广泛举措相结合。这项工作是特别教育价值的学生，由于低频电动力学技术，就业，并发现在研究和私营企业的广泛应用。以约翰霍普金斯物理学博览会为形式的公共外联活动也正在实现。 技术描述：相互作用、无序及其相互作用是现代凝聚态物理学的中心主题。 该项目正在探索最近引起强烈兴趣的两个领域，其中强相互作用和无序合谋创造量子物质的奇异低温态：二维超导体绝缘体量子相变和“多体局域化”现象。 他们正在研究的一些新的低能量电动探针可在PI的组。 二维超导体-超导绝缘体相变（2DSIT）是量子相变（QPT）的一个典型例子，而量子相变是凝聚态物理中的一个重要研究课题。低温微波光谱学的最新进展正在被利用，以提供第一个真正的动态信息，在薄超导（InO）薄膜的相变。 多体定域化现象也在研究之中. 最近Basko，Aleiner和Altshirt证明，对于具有足够强无序的系统，局域化可以阻止能量或粒子传输，因此系统无法平衡并成为自己的热浴。 这意味着（在没有像声子那样的离域自由度的情况下）应该有一个有限的温度局域化跃迁。 我们正在研究电子玻璃系统和无序伊辛链的弛豫动力学，并寻找太赫兹弛豫随光泵浦参数的变化。

Nontechnical description:It is hardly an exaggeration that most of what we know about physical systems comes from their response to perturbations at their characteristic frequencies. For instance, the fundamental tone of a plucked violin string depends on the length of the string, the tension in it, and its thickness. This is true from the acoustics of a violin to the energies of atoms. Unfortunately the natural frequency scales of many solid materials fall in a spectral range, which has been prohibitively difficult to access technically until recently. This project takes advantage of recent dramatic technical advances in THz and microwave spectroscopy to characterize the natural frequency scales of disordered solids. Material systems like superconductors, which can conduct electricity without resistance and various insulating states are being studied. The investigations performed herein give essential information to develop new materials with important technological implications. These technological developments are coupled to a broad initiative in education and outreach. The work is of particular educational value to students owing to the low frequency electrodynamics techniques that are employed and which are finding broad application in research and private industry. Public outreach activities in the form of the Johns Hopkins Physics Fair is also being realized. Technical description:Interactions, disorder, and their interplay is a central theme of modern condensed matter physics. This project is exploring two areas of intense recent interest where strong interactions and disorder conspire to create exotic low temperature states of quantum matter: the 2D superconductor insulator quantum phase transition and the phenomena of ``many-­body localization". They are being investigated by a number of novel low energy electrodynamic probes available in the PI's group. The 2D superconductor-­insulator transition (2D SIT) is a paradigmatic example of a quantum phase transition (QPT) -­ a topic of much interest in the condensed matter physics. Recent advances in low temperature microwave spectroscopies are being exploited to provide the first true dynamic information about this phase transition in thin superconducting (InO) films. The phenomena of many-­body localization is also being investigated. Recently Basko, Aleiner, and Altshuler demonstrated that for systems with strong enough disorder, localization can prevent energy or particle transport, so that the system fails to equilibrate and to be its own heat bath. This implies that (in the absence of delocalized degrees of freedom like phonons) there should be a finite temperature localization transition. We are investigating the relaxation dynamics of both electron glass systems and disordered Ising chains and among other things looking for changes in the THz relaxation as function of optical pump parameters.