Tunneling Experiments of Recent Interest: Zero Bias Conductance Peak and Pseudogap Measurement

在这个项目中，新的和更复杂的隧道实验将在高T_c超导体上进行。具体来说，将对超导体进行零偏置电导峰(ZBCP)和伪隙测量。这个项目由三个部分组成。第一部分研究了ZBCP在不同实验条件下的响应，如1)隧道方向，2)磁性和非磁性杂质的存在，以及3)微波辐射的存在。第二部分对欠掺杂Bi2Sr2CaCu2O8-d(BSCCO)中的伪隙进行了仔细的测量。我们将研究赝隙与氧含量、磁场和温度的关系。我们还将利用高温超导体到高温超导的隧道效应来研究超导态中常见的倾角特征与伪隙的关系。在项目的第三部分，将进行两个新的实验来研究ZBCP和共同的伪隙状态。第一个实验是探索当T_c时，欠掺杂BSCCO中安德列夫反射的发生。如果在赝隙位相中存在预形变对，则Andreev反射将在隧道电导曲线上产生一个弱的ZBCP。另一种技术是使用巨磁电阻(CMR)材料作为对电极。自旋极化的电子会降低ZBCP的高度。如果赝隙与欠掺杂高T_c超导体中的预成对有关，这些自旋极化的电子也会抑制赝隙。现在公认的是，高温超导体表现出许多其他常规(普通)超导体所没有的有趣的性质。普通超导体只能在非常低的温度下工作，但已经被用于许多先进技术中。人们正在努力改善高温超导体的行为，使其能够更容易、更经济地集成到技术设备中，如远距离电力传输、储能设备、电机等。然而，这些应用确实取决于对高温超导的更好理解。目前还没有一个令人满意的高温超导基本理论，这项研究针对的是临界实验的性能，以帮助建立一个可接受的理论。这项研究将涉及研究生、本科生和博士后研究助理，他们因此将接受当代凝聚态物理和材料科学前沿领域之一的培训。这项培训将为他们在21世纪的技术劳动力中从事富有成效的职业生涯做好准备。

9972071NgIn this project new and more sophisticated tunneling experiments will be performed on high-Tc superconductors. Specifically, Zero Bias Conductance Peak (ZBCP) and pseudogap measurements will be performed on superconductors. This project consists of three parts. The first part consists of the study of the response of ZBCP under different experimental conditions such as 1) the tunneling direction, 2) the presence of both magnetic and non-magnetic barrier impurities, and 3) the presence of microwave radiation. The second part involves careful measurements on the pseudogap found in underdoped Bi2Sr2CaCu2O8-d (BSCCO). The dependence of the pseudogap on the oxygen content, magnetic field, and the temperature will be investigated. The relationship between the dip feature commonly observed in the superconducting state and the pseudogap will also be investigated by means of high Tc superconductor - to - high Tc superconductor tunneling. In the third part of the project, two new experiments will be performed to study the ZBCP and also the pseudogap state in common. The first experiment is to search for the occurrence of Andreev reflection in underdoped BSCCO when T Tc. If there are pre-form pairs in the pseudogap phase, then Andreev reflection will produce a weak ZBCP in the tunneling conductance curve. The other technique is to use colossal magnetoresistance (CMR) material as a counter electrode. The spin polarized electrons will depress the height of ZBCP. These spin-polarized electrons will also suppress the pseudogap if the pseudogap is related to the pair pre-formation in underdoped high Tc superconductors. %%%It is now well established that high-temperature superconductors demonstrate many interesting properties that do not appear in other conventional (ordinary) superconductors. Ordinary superconductors operate at only very low temperatures yet are already used in many advanced technologies. There is a great effort underway to improve the behavior of high-temperature superconductors to allow them to be more easily and more economically integrated into technological devices, such as the transmission of electrical power over long distances, energy storage devices, electric motors, etc. These applications do depend, however, on a better understanding of high-temperature superconductivity. A satisfactory fundamental theory of high-temperature superconductivity is not yet available and this research is directed to the performance of critical experiments to assist in the establishment of an acceptable theory. This research will involve graduate as well as undergraduate students and postdoctoral research associates who will thereby receive training in one of the forefront areas of contemporary condensed-matter physics and materials science. This training will prepare them for productive careers in the technological work force during the 21st Century.