Transport, Magnetism and Superconductivity in Strongly Correlated and Frustrated Lattices

该奖项支持强相关电子材料领域的理论研究和教育。PI将开展理论研究，研究高度挫折晶格中的传输，磁性和超导行为。这项工作的动机是最近发现的磁性和不寻常的超导低于5 K，和异常的输运行为的钠钴氧化物系统Na_xCoO2。这些金属系统显示出与一些最好的半导体一样大的热电势;热电势也强烈地依赖于磁场。霍尔效应是最不寻常的，因为它不随温度而饱和。极端的II型超导电性发生在水合作用。在相图中出现了不寻常的磁长程有序。诸如此类的实验发现挑战了金属基本理论的原则，表明在这些系统中强多体相关性的重要作用。PI将使用适用于适当模型的分析和数值技术相结合，以研究磁性和超导状态的传输特性和发生以及性质。更广泛的影响：对钴酸盐的研究最终可能会提高我们对其他强关联电子系统的理解，例如高温超导体，这已经被证明是非常具有智力挑战性的。 从技术角度来看，钴酸盐本身可能非常重要-它们的大热电性与低电阻相结合，使它们能够在高温下实现最知名的品质因数。它们还与更轻的碱原子钴酸盐LixCoO 2有关，这是轻质锂电池技术的核心。Liy-xNaxCoO 2等材料在本研究中作为自然可能性出现，可能会催化热电和电池技术的新融合，从而产生新技术。该奖项还支持高级理论凝聚态物理学的研究生水平教育。该奖项支持强相关电子材料的理论研究和教育，重点是理解最近钴酸盐化合物Na_xCoO_2实验中揭示的异常性质和有序状态。这些实验表明，钴矿不同于普通金属。它们还显示出不寻常的磁性和超导状态。据信，由于基础晶体结构的几何形状（几何挫折）与电子之间的强相互作用相结合，电子自旋之间的相互作用不能得到满足，导致这些材料表现出异常性质。这些强相关电子材料的一些性质，如它们的组合大的热电势和低电阻，表明潜在的技术应用和新技术的潜力，如上所述。这些材料的研究，像其他强关联电子材料，导致新的基础凝聚态物理学的发现。该奖项还支持高级理论凝聚态物理学的研究生水平教育。***

This award supports theoretical research and education in the area of strongly correlated electron materials. The PI will carry out theoretical research to study transport, magnetic and superconducting behavior in highly frustrated lattices. This work is motivated by very recent discoveries of magnetism and unusual superconductivity below ~5 K, and of anomalous transport behavior in the sodium cobalt oxide system Na_xCoO2. These metallic systems display a thermopower as large as some of the best semiconductors; the thermopower is also strongly magnetic field dependent. The Hall effect is most unusual in that there is no saturation with temperature. Extreme type II superconductivity occurs on hydration. Unusual magnetic long-ranged order occurs in the phase diagram. Experimental findings such as these challenge the tenets of the basic theory of metals, suggesting an important role for strong many-body correlations in these systems. The PI will use a combination of analytical and numerical techniques applied to appropriate models to study the transport properties and the occurrence, as well as the nature, of the magnetic and superconducting states. The research will focus on the especially strong many-body renormalizations revealed by recent experiments.Broader impacts: Studying the cobaltates may ultimately improve our understanding of other strongly correlated electron systems, such as the high temperature superconductors, which have proven to be very intellectually challenging. The cobaltates are potentially very important from a technological point of view in their own right - their large thermopower combined with low resistance enables them to achieve the best-known figure of merit at high temperature. They are also related to the lighter alkali atom cobaltate LixCoO2 that is central to lightweight lithium battery technology. Materials such as Liy-xNaxCoO2, that arise as natural possibilities in this study, may catalyze a novel fusion of thermoelectric and battery technologies leading to new technologies. This award also supports graduate level education in advanced theoretical condensed matter physics. %%%This award supports theoretical research and education on strongly correlated electron materials with a focus on understanding the anomalous properties and ordered states revealed in recent experiments on cobaltite compounds, Na_xCoO_2. These experiments show that the cobaltites are unlike ordinary metals. They also show unusual magnetic and superconducting states. It is believed that the inability of the interactions between electron spins to be satisfied because of the geometry of the underlying crystal structure (geometric frustration) combined with strong interactions among electrons, leads to the anomalous properties exhibited by these materials. Some properties of these strongly correlated electron materials, like their combined large thermopower and low resistance, suggest potential technological applications and the potential for new technologies, as suggested above. The study of these materials, like other strongly correlated-electron materials, leads to the discovery of new fundamental condensed matter physics. This award also supports graduate level education in advanced theoretical condensed matter physics. ***