Theoretical Studies of Near-Critical, Strongly Interacting Electron Systems

技术摘要：该奖项支持凝聚态物理领域的理论研究和教育，重点是描述量子临界点(QCP)附近的系统，在QCP附近，巡回费米子系统变得不稳定，无论是自旋还是电荷密度波有序。在QCP附近，与近乎无隙的、过抑制的序参数场的涨落相互作用，破坏了电子的费米液体行为，直到很低的温度。同样的相互作用导致了非相干、非费米液体类激发之间的配对。PI将集中在铜酸盐超导体、巡回铁磁体和重费米子材料上。这些研究的最终目的是了解临界红外发散、Mott-Heisenberg物理、超导电性和有效相互作用中远程动态分量的存在之间的相互作用。首先，PI计划研究反铁磁不稳定性附近的巡回费米子系统。PI的目的是研究超导性和非相干费米子成束缚自旋单态的非BCS配对之间的相互作用，以及一旦相互作用变得与费米子带宽相当时莫特-海森伯格物理的出现。PI还建议在电子掺杂的铜酸盐上测试电子-玻色子模型，并寻找定性区分配对的磁性和声子机制的指纹。其次，PI计划研究波美兰丘克不稳定性附近的各向同性巡回费米子系统。他的主要目标是确定非相干费米子的Eliashberg理论的稳定性，分析在什么条件下长程动力学相互作用破坏了连续的QCP，研究可能的中间螺旋序参数组态，并研究QCP附近的输运性质，特别是umclapp散射的作用。这项研究将涉及到华盛顿大学研究生的培训和国际合作。智力价值：对QCP附近的系统行为的分析具有基本的重要性，并具有很高的实验和理论兴趣。这项研究将促进我们对QCP附近系统行为的了解，也将成为掺杂Mott绝缘体研究和近临界费米液体研究之间的桥梁。广泛影响：该奖项还支持学生在高级理论凝聚态物理和国际合作方面的培训。非技术总结：该奖项支持凝聚态物理领域的理论研究和教育。PI将研究在绝对零度时发生的一种有趣的相变。物质不同状态之间的转换是由基本的量子力学原理驱动的，而不是温度。这种相变可以深刻地影响电子在室温甚至更高温度下的行为方式。量子相变可能在理解一类材料的高温超导现象和其他性质方面发挥关键作用，其中电子之间的强烈相互作用导致它们运动的关联和电子物质的新状态。PI的研究旨在了解当材料接近量子相变时，电子的异常行为如何导致超导。该奖项还支持对学生进行高级理论凝聚态物理的培训。

TECHNICAL SUMMARY:This award supports theoretical research and education in the area of condensed matter physics with a focus on characterizing systems near quantum critical points (QCP), where an itinerant fermion system becomes unstable with respect to either spin or charge density wave ordering. Near a QCP, the interaction with fluctuations of a near-gapless, overdamped order parameter field destroys Fermi liquid behavior of electrons down to very low temperatures.The same interaction gives rise to pairing between incoherent, non-Fermi-liquid-like excitations. The PI will focus on the cuprate superconductors, itinerant ferromagnets, and heavy fermion materials. The ultimate goal of the studies is to understand the interplay between infrared divergences at criticality, Mott-Heisenberg physics, superconductivity, and the presence of the long-range dynamic component in the effective interaction.The proposed studies are divided into two classes. First, the PI plans to study itinerant fermionic systems near an antiferromagnetic instability. The PI aims to study the interplay between the superconductivity and the non-BCS pairing of incoherent fermions into bound spin singlets, and the emergence of the Mott-Heisenberg physics once the interaction becomes comparable to the fermionic bandwidth. The PI also proposes to test an electron-boson model on electron-doped cuprates, and to search for the fingerprints that qualitatively distinguish between magnetic and phononic mechanisms for the pairing. Second, the PI plans to study isotropic itinerant fermionic systems near a Pomeranchuk instability. His main goals are to determine the stability of the Eliashberg theory for incoherent fermions, to analyze under what conditions long-range dynamic interaction destroys a continuous QCP, to study a possible intermediate spiral order parameter configuration, and to study transport properties near QCP, particularly the role of umklapp scattering.The research will involve the training of graduate students at UW and international collaborations. Intellectual merit: The analysis of the system behavior near a QCP is of fundamental importance and of high experimental and theoretical interest. The research will advance our knowledge of system behavior near a QCP, and will also serve as a bridge between the studies of doped Mott insulator and the studies of a near-critical Fermi liquid.Broader impact: This award also supports the training of students in advanced theoretical condensed matter physics and international collaboration.NON-TECHNICAL SUMMARY:This award supports theoretical research and education in the area of condensed matter physics. The PI will study an interesting kind of phase transition that occurs at the absolute zero of temperature. The transformation between different states of matter is driven by fundamental quantum mechanical principles rather then temperature. Such phase transitions can profoundly affect way electrons behave at temperatures as high as room temperature and possibly higher. Quantum phase transitions may play a key role in understanding the phenomenon of high temperature superconductivity and other properties of a class of materials where strong interactions among electrons lead to correlations in their motion and new states of electronic matter. The PI's research aims to understand how the unusual behavior of electrons that occurs when a material is close to a quantum phase transition can lead to superconductivity. This award also supports the training of students in advanced theoretical condensed matter physics.