Thermoelectric and Thermal Transport in Disordered and Strongly Correlated Electron Systems

该奖项支持各种系统中热电和热输运的理论研究，其中熵的基本部分存储在集体模式的集合中。这些模式补充了准粒子激励，并描述了不同类型的临界涨落。一般来说，显示大热功率的有希望的候选系统是那些强波动使用于寻找低温热性能的常规索默菲尔德展开失效的系统。作为一种理论工具，一种基于量子动力学方程的新开发方案将被应用，从而受益于PI最近在研究超导体中能思特效应方面的经验。对能斯特效应的分析表明，热输运比普通电子输运更能有效地研究涨落效应。该方法的通用性使它能够解释由临界涨落介导的不同种类的电子-电子相互作用。该研究将增强对非费米液体行为系统中热输运的理论认识。理论上要解决的问题包括由电子-电子相互作用组合的无序引起的金属-绝缘体转变附近的热功率，以及流动电子系统中的近量子相变。因此，这项研究将有助于发展量子临界点附近热电输运或金属-绝缘体跃迁的概念性图景。特别是，它可能会产生一个由波动决定的新的简单热功率公式，可以用来代替莫特的公式。在本研究中获得的对强相互作用系统中热电的基本理解将有助于在寻求具有强热电的材料时做出明智的选择。这些材料可以用来制造新的冷却器，这是低温实验物理和应用仪器的进步所需要的。培训初级研究人员在任何学术环境中都是至关重要的。除了热现象的物理，参与研究将为年轻科学家提供凝聚态理论和量子动力学的先进方法的培训。该奖项支持对某些材料中热流和电荷流的理论研究，其中电子的贡献主导了热流。PI将使用先进的理论技术来研究特别有趣的情况，包括：(1)由于杂质和缺陷以及电子之间的强相互作用而接近从金属转变为绝缘体的材料，以及(2)接近量子相变的材料。不像普通的相变是由热波动驱动的，例如在32度时从冰到水的转变，量子相变是由海森堡著名的不确定性原理的量子波动驱动的，可以在温度的绝对零度下发生，在熟悉的华氏温标上是寒冷的-460度。(3)局限于二维空间的电子气体，可以在人造半导体材料结构中产生；(4)自旋液体，预计在某些材料中出现，其中电子之间的相互作用不能同时得到满足。人们可能天真地认为这些材料会变成磁铁，但实际上，这些受挫的相互作用导致了一种没有磁性秩序的液态电子。PI将使用量子力学方程来描述电子在非平衡状态下的净运动，比如当材料之间存在温差时。这一研究将促进我们对具有强相互作用电子的材料中热量和电荷的输运的理解，从而显示出电子物质的新状态或有趣的现象。PI的研究可能会带来一种有趣的方式来探索材料的特性和电子物质的新状态。在本研究中获得的对强相互作用系统中热电的基本理解将有助于在寻求具有强热电的材料时做出明智的选择。热功率是测量当触点之间保持电压差时试样中产生的温差。这就是为什么这种材料可以用于制造具有广泛潜在技术应用的新型冷却装置的原因。培训初级研究人员在任何学术环境中都是至关重要的。除了热现象的物理，参与研究将为年轻科学家提供凝聚态理论和量子动力学的先进方法的培训。

TECHNICAL SUMMARYThis award supports theoretical research of thermoelectric and thermal transport in various systems, for which an essential fraction of the entropy is stored in an ensemble of collective modes. These modes complement quasi-particle excitations and describe different kinds of critical fluctuations. Generally, promising candidate systems for displaying large thermopower are those in which strong fluctuations invalidate the regular Sommerfeld expansion used for finding thermal properties at low temperatures.As a theoretical tool, a newly developed scheme based on quantum kinetic equations will be applied, thereby profiting from the recent experience of the PI in studying the Nernst effect in superconductors. Analysis of the Nernst effect showed that thermal transport can be a more effective tool for studying fluctuation effects than the ordinary electronic transport. The generality of the method makes it possible to account for different kinds of electron-electron interactions mediated by critical fluctuations. The research will enhance the theoretical understanding of thermal transport in systems which exhibit non-Fermi liquid behavior. The issues to be addressed theoretically include thermopower near the metal-insulator transition caused by disorder in combination with electron-electron interactions, and near quantum phase transitions in systems of itinerant electrons. As a result, the research will help to develop a conceptual picture of thermoelectric transport in the vicinity of a quantum critical point or the metal-insulator transition. In particular, it may result in a new simple formula for the thermopower determined by fluctuations that can be used in place of Mott's formula. The fundamental understanding of thermoelectricity in strongly interacting systems acquired in this research will help to make informed choices in the quest for materials with strong thermopower. Such materials can be used for creating new coolers, which are needed for progress in low temperature experimental physics and applied instrumentation.Training junior researchers is of paramount importance in any academic setting. Besides physics of thermal phenomena, the participation in the research will provide training of the young scientists in advanced methods of condensed matter theory and quantum kinetics.NON-TECHNICAL SUMMARYThis award supports theoretical research on the flow of heat and electric charge in certain materials for which contributions from electrons dominate heat flow. The PI will use advanced theoretical techniques to investigate particularly interesting cases, including: (1) materials that are near a transformation from a metal to an insulator due to impurities and imperfections and strong interactions between electrons, and(2) materials that are near a quantum phase transition. Unlike an ordinary phase transition which is driven by thermal fluctuations, for example the transition from ice to water at 32 degrees, a quantum phase transition is driven by the quantum fluctuations of Heisenberg's famous uncertainty principle and can occur at the absolute zero of temperature, a frigid -460 degrees on the familiar Fahrenheit scale. (3) a gas of electrons confined to two dimensions which can be created in artificial semiconductor material structures,(4) spin liquids which are predicted to arise in certain materials where the interactions between electrons cannot all be simultaneously satisfied. Naively, one might think these materials will become magnets, but rather these frustrated interactions lead to a liquid-like state of electrons without magnetic order. The PI will use quantum mechanical equations that can describe the net movement of electrons in states out of equilibrium, such as when there is a difference of temperature across a material. This research will advance our understanding of the transport of heat and charge in materials with strongly interacting electrons which exhibit new states of electronic matter or interesting phenomena. The PI's research may lead to an interesting way to probe the properties of materials and new states of electronic matter. The fundamental understanding of thermoelectricity in strongly interacting systems acquired in this research will help to make informed choices in the quest for materials with strong thermopower. The thermopower is a measure for the temperature difference developing in a sample when a voltage difference is maintained between the contacts. This is why such materials can be used for creating new cooling devices which have a wide range of potential technological applications.Training junior researchers is of paramount importance in any academic setting. Besides physics of thermal phenomena, the participation in the research will provide training of the young scientists in advanced methods of condensed matter theory and quantum kinetics.