Probing Two Particle Correlations by Angle Resolved Photoemission

高温超导体正迅速成为国家能源需求的重要组成部分。预计它们将在帮助稳定国家电网的设备方面产生最大的影响，到2010年，国家电网的需求预计将翻一番，或者在向由于能源成本增加而正在重新城市化的城市提供足够的电力方面产生最大的影响。虽然现在有一些商业应用，但材料的进一步改进是必要的。从发现新材料、了解超导的起源、提高超导转变温度和改进第二代导体开始，有几种方法是实现这一改进所必需的。正是在对这些复杂的新材料的理解中，本提案将通过开发新的实验技术来促进这项事业。首先是直接探测电子配对，这是导致超导性的基本过程。这项工作将解决一个长期争论的问题，即电子是否在明显高于超导开始的温度下形成瞬态对，在一种被称为赝隙的奇怪状态下。如果这种配对可以直接观察到，那么人们就可以通过操纵控制配对的适当数量来找到提高超导体临界温度的方法。第二个实验将研究施加在材料上的电流如何影响这种配对及其破坏。人们相信，在不太完美的材料中，电流通过改变成对电子之间的相位来影响超导性，而不是通过自行产生磁场。此外，这项工作将继续我们培养少数族裔在学术界和工业界取得成功的良好记录。本项目旨在确定高温超导体中的电子是否在超导转变温度以上，在尚不清楚的赝隙相中配对。长期以来，人们一直在争论赝隙态是否起源于单个电子对的配对，当温度降低时，这些电子对凝聚成宏观超导态时，它们的相位都变得相干。关于赝隙的起源，还有其他与超导性无关的说法。到目前为止，还没有直接的证据证明这种配对，或者它的存在。这项工作提出了一种新的实验技术，当一对电子吸收单个光子时，它们就会被探测到，这对电子会因光电效应而断裂并同时发射。该项目还将检查施加电流下电子的状态。在非最佳掺杂的高温超导体中，超导性可能会被施加的电流改变对之间的相位而不是通常的自生磁场涡的影响所破坏。学生和博士后将接触到凝聚态物理前沿的工作，因为这项工作涉及到广泛的国内和国际合作，这些合作涉及到培养样本的小组，在相同的样本上进行各种实验，并将理论工作应用于开发新的数据分析方法。

Non-technicalHigh temperature superconductors are fast becoming important for the country's energy needs. They are expected to have their greatest impact in devices which help stabilize the national power grid, where demand is expected to double by 2010, or in delivering sufficient power to cities undergoing re-urbanization as a result of increasing energy costs. Although some commercial applications are now available, further improvement in materials is imperative. Several approaches are necessary for this improvement, starting with the discovery of new materials, understanding the origin of superconductivity, the increase in superconducting transition temperatures, and the improvement of 2nd generation conductors. It is in the understanding of these complex new materials that this proposal will contribute to this enterprise, by developing new experimental techniques. First is the direct detection of pairing of electrons, the basic process that leads to superconductivity. The work will address the long-debated question of whether electrons form transient pairs at temperatures significantly higher than those where superconductivity sets in, in a strange state called the pseudogap. If this pairing can be directly observed, then one could find ways to increase the critical temperature of superconductors by manipulating the proper quantities that control the pairing. The second experiment will study how this pairing, and its destruction, are affected by electrical currents applied to the material. It is believed that in less than perfect materials, which naturally occur in large scale manufacturing, electric currents affect superconductivity by changing the phase between paired electrons, rather than by the self-generation of magnetic fields. In addition, this work will continue our excellent track record of training minorities for success in academia and industry.TechnicalThis project aims to determine whether the electrons in the high temperature superconductors pair above the superconducting transition temperature, in the ill-understood pseudogap phase. It has long been debated whether the pseudogap state has its origin in the pairing of electrons in individual pairs, which all become coherent in phase as the pairs condense into a macroscopic superconducting state as the temperature is lowered. There are other proposals for the origin of the pseudogap which are unrelated to superconductivity. So far there is no direct proof of this pairing, or its absence. This work proposes a novel experimental technique, where a pair of electrons is detected as they absorb a single photon, which breaks the pair and causes them to be simultaneously emitted by the photoelectric effect. The project will also examine the state of electrons under an applied current. In less than optimally doped high temperature superconductors, superconductivity might be destroyed by the alteration of the phase between pairs by the applied current, rather than the usual effect of vortices from self-generated magnetic fields. The students and post-doctoral fellows are exposed to work at the frontier of condensed matter physics, as this work involves an extensive national and international collaboration between groups that grow samples, carry out a variety of experiments on the same samples, and apply theoretical work to the development of new methods of data analysis.