Measuring the Electron Spectral Function by Angle-Resolved Photoemission

这个项目的目标是利用角度分辨光电发射(ARPES)技术来确定高温超导体中载流子的性质。这个谱函数表示在多体系统中添加或移除一个电子的概率。在这些材料中，电子彼此之间以及与其他集体激发(如自旋波)强烈相互作用。谱函数提供了有关这些相互作用的非常有用的信息。在适当的条件下，谱函数可以被操纵来产生电子的自能，这是现代强相互作用多体系统理论可以直接计算的量。这项工作旨在研究高温超导体不同状态下的自能。这个项目还试图了解当材料经历超导转变时，费米面是如何改变形状的。该小组最近的工作发现，在不同动量下的电子态在不同的温度下变得空隙，导致费米面分裂成不相连的费米弧，费米弧随着T的减小而收缩，最终坍塌到T_c以下的超导基态点。这种新的行为，其中费米表面不像传统金属那样在动量空间中形成连续的轮廓，这是史无前例的，因为它发生在没有长程有序的情况下。%高温超导体是在冷却到液体空气的温度时没有任何电阻地携带电流的材料。这项利用角度分辨光电发射(ARPES)技术的研究旨在帮助理解电子如何在高温超导体中运动以携带电流。这些新材料在导电方式上不同于所有以前已知的材料。现在，在它们被发现10年后，这些机制仍然没有完全被理解。这项工作旨在将ARPES测量的物理量与使用其他技术测量的量联系起来。作为一个序列，这个项目为希望在我们对新材料的理解的前沿工作的研究生提供了极好的研究机会。

9974401CampuzanoThe goal of this project is to determine the nature of the charge carriers in the high temperature superconductors using the technique of angle-resolved photoemission (ARPES). This spectral function represents the probability of adding or removing an electron from a many-body system. In these materials, the electrons strongly interact with one another and with other collective excitations such as spin waves. The spectral function provides very useful information about these interactions. Under suitable conditions, the spectral function can be manipulated to yield the self energy of the electrons, which is the quantity directly calculable by modern theories of strongly interacting many-body systems. This work aims to study the self-energy in the different states of high temperature superconductors. This project also seeks to understand how the Fermi surface changes shape when the material undergoes the superconducting transition. Recent work by this group has found the remarkable effect that electronic states at different momenta become gapped at different temperatures, leading to a break up of the Fermi surface into disconnected Fermi arcs which shrink with decreasing T, eventually collapsing to points in the superconducting ground state below Tc. This novel behavior, where the Fermi surface does not form a continuous contour in momentum space as in conventional metals, is unprecedented in that it occurs in the absence of long range order.%%%The high temperature superconductors are materials that carry current without any resistance when cooled to the temperature of liquid air. This research using the technique of angle-resolved photoemission (ARPES) is designed help reach an understanding of how electrons move in the high temperature superconductors to carry electrical current. These new materials are unlike all previously known materials in the way they conduct electricity. Now, 10 years after their discovery, the mechanisms are still not fully understood. This work aims to connect the physical quantities measured by ARPES to quantities measured using other techniques. As aconsequence, this project provides excellent research opportunities for graduate students who wish to work at the frontier of our understanding of new materials.***