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都来自于它们对其特征频率的扰动的反应。例如，一根拨动的小提琴弦的基音取决于弦的长度、弦中的张力和弦的厚度。从小提琴的声学到原子的能量，都是如此。不幸的是，许多固体材料的自然频率范围落在一个光谱范围内，直到最近，在技术上一直很难达到这个范围。这个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。人们正在研究像超导体这样的材料系统，这种材料系统可以在没有电阻的情况下导电，并处于各种绝缘状态。这里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辅相成。这项工作对学生具有特别的教育价值，因为所使用的低频电动力学技术在研究和私营工业中得到了广泛的应用。约翰霍普金斯大学物理博览会等形式的公众宣传活动也正在实现。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。这个项目正在探索最近引起人们强烈兴趣的两个领域，在这些领域中，强烈的相互作用和无序共同创造了量子物质的奇异低温状态：2D超导绝缘体的量子相变和“多体局域化”现象。他们正在被PI‘s小组提供的一些新的低能量电动探针所研究。二维超导体-绝缘体相变(2D SIT)是量子相变(QPT)的一个范例--这是凝聚态物理中非常感兴趣的一个话题。低温微波光谱的最新进展正在被用来提供关于薄膜超导(InO)薄膜中这种相变的第一个真实的动态信息。多体定位现象也在调查中。最近，Basko、Aleiner和Altshuler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，从而使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，其中包括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.