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

非技术描述：毫不夸张地说，我们对物理系统的大部分了解来自于它们对其特征频率上的扰动的响应。例如，拨弦的小提琴弦的基本音取决于弦的长度、张力和厚度。从小提琴的音质到原子的能量，都是如此。不幸的是，许多固体材料的固有频率尺度落在一个光谱范围内，直到最近才从技术上难以获得。该项目利用了最近在太赫兹和微波光谱方面的巨大技术进步来表征无序固体的固有频率尺度。诸如超导体之类的材料系统正在被研究，它可以无电阻地导电，并具有各种绝缘状态。本文所进行的研究为开发具有重要技术意义的新材料提供了必要的信息。这些技术发展与教育和外联方面的广泛倡议相结合。由于所采用的低频电动力学技术在研究和私营工业中得到广泛应用，这项工作对学生具有特别的教育价值。以约翰霍普金斯物理博览会的形式开展的公众宣传活动也正在实现。技术描述：相互作用、无序和它们的相互作用是现代凝聚态物理的中心主题。该项目正在探索两个最近备受关注的领域，在这些领域中，强相互作用和无序共同创造了奇异的低温态量子物质：二维超导体绝缘体量子相变和“多体局部化”现象。PI的团队正在用一些新型的低能电动力探针对它们进行研究。二维超导体-绝缘体转变（2D SIT）是量子相变（QPT）的一个典型例子，量子相变是凝聚态物理学中一个非常感兴趣的话题。低温微波光谱的最新进展正在被利用来提供关于薄超导（InO）薄膜相变的第一个真正的动态信息。多体定位现象也在研究中。最近，Basko、Aleiner和Altshuler证明，对于无序程度足够强的系统，局域化可以阻止能量或粒子输运，从而使系统无法平衡，无法成为自己的热浴池。这意味着（在没有像声子这样的离域自由度的情况下）应该有一个有限的温度局域化转变。我们正在研究电子玻璃系统和无序伊辛链的弛豫动力学，并在其他方面寻找太赫兹弛豫随光泵参数的变化。

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.