Probing Two Particle Correlations by Angle Resolved Photoemission

非技术性高温超导体对国家的能源需求正迅速变得重要起来。预计它们将在有助于稳定国家电网的设备方面产生最大影响，预计到2010年，国家电网的需求将翻一番，或者为由于能源成本上升而正在进行再城市化的城市提供足够的电力。虽然现在已经有了一些商业应用，但材料的进一步改进势在必行。这种改进需要几种方法，从发现新材料开始，了解超导的起源，超导转变温度的提高，以及第二代导体的改进。正是在对这些复杂的新材料的理解中，这项提议将通过开发新的实验技术来为这项事业做出贡献。首先是直接探测电子配对，这是导致超导的基本过程。这项工作将解决一个长期争论的问题，即电子是否在比超导开始时的温度高得多的温度下形成瞬时对，处于一种称为赝隙的奇怪状态。如果可以直接观察到这种配对，那么就可以通过操纵控制这种配对的适当的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到材料上的电流如何影响这种配对及其破坏。人们认为，在大规模制造中自然会出现的不太完美的材料中，电流通过改变成对电子之间的相位来影响超导电性，而不是通过磁场的自身产生。此外，这项工作将继续我们在学术界和工业界培训少数族裔取得成功的出色记录。技术本项目旨在确定高温超导体中的电子是否在超导体转变温度以上，处于令人费解的伪隙阶段。长期以来，人们一直在争论伪隙状态是否起源于单个电子对中的电子配对，随着温度的降低，随着电子对凝聚成宏观超导状态，这些电子对都会在相位上变得相干。对于伪隙的起源，还有其他一些与超导无关的说法。到目前为止，还没有直接的证据证明这种配对，或者没有这种配对。这项工作提出了一种新的实验技术，其中一对电子在吸收单个光子时被检测到，这会破坏这对电子，并使它们同时通过光电效应发射。该项目还将研究电子在外加电流下的状态。在低于最佳掺杂的高温超导体中，超导电性的破坏可能是由于外加电流改变了超导体对之间的位相，而不是通常的自产生磁场的涡旋效应。学生和博士后研究员将接触到凝聚态物理前沿的工作，因为这项工作涉及团队之间广泛的国内和国际合作，这些团队种植样本，对相同的样本进行各种实验，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.