CAREER: Anisotropic Femtosecond Spectroscopy of High-Tc Superconductors

9734131施罗德这是一个职业奖，将使用强大、复杂和偏振敏感的时间分辨超快光谱技术研究本质各向异性高TC铜酸盐超导体的基本性质。利用超宽带飞秒太赫兹(THz)探测脉冲(由50fs光脉冲的光整流产生)，通过扰动复杂电导率产生的反射率的变化，对光泵脉冲引起的高温超导体的远红外瞬变响应进行光谱时间解析。由于线偏振太赫兹探测脉冲的光谱范围包括超导带隙2A，这项技术将被用来直接监测光学诱导的各向异性序参数A的微扰，欠掺杂材料中的赝隙，以及使用非孪晶的Y和Ba基铜酸盐晶体的CuO层和链之间的瞬时面间和面内耦合。此外，为了帮助理解时间分辨的太赫兹光谱，我们将使用双光子激发态角分辨光电子能谱来确定费米能级以上光耦合空态的相关特性(寿命和动量)。所有测量都将作为TITC的功能来执行，以阐明温度相关性。这些精心设计的超快光谱测量的结果应该会对我们理解高温超导体的独特性质产生重大影响，其方式与半导体物理中类似的飞秒光学技术所提供的方式平行。教育部分将包括物理专业的本科生和芝加哥地区高中的学生参与与该项目目标相关的调查实验室的研究。%这是一个职业奖，它使用复杂的光学方法研究高温超导体S。1986年发现的铜氧化物陶瓷材料在液氮(-3华氏度)(而不是液氦(-450华氏度))温度下表现出零电阻，点燃了人们对超导技术的兴趣，将其作为一种显著降低能源分配成本的手段，开发高效的高速悬浮交通工具，并制造超高速电子开关。然而，尽管对高温超导体(HTSCs)的性质进行了十年令人兴奋的研究，但能够清楚地了解这些独特材料中超导电性的物理机制的最终实验还没有到来。这项研究计划的目标是利用今天的激光技术提供的亚皮秒(小于十亿分之一秒)的时间分辨率来研究高温超导中发生的基本物理过程。具体地说，将使用远红外辐射的超短脉冲来监测HTSC的响应，以努力及时解决这些陶瓷材料中超导电性的机制。这些超快光学研究将开启超导电性研究的新领域，利用辐射直接监测超导态的电子动力学。这些新颖的光谱研究结果应该会对我们理解高温超导材料的独特性质产生重大影响，这反过来可能导致超导体在更高温度下工作的发展。事实上，类似的超快光学技术已经提高了我们对日常半导体器件的理解和设计。教育部分将包括物理专业的本科生和芝加哥地区高中的学生参与与该项目目标相关的调查实验室的研究。***

9734131 Schroeder This is a CAREER Award which will investigate the fundamental properties of intrinsically anisotropic high-TC cuprate superconductors using powerful, sophisticated, and polarization-sensitive time-resolved ultrafast spectroscopic techniques. An ultrabroadband femtosecond terahertz (THz) probe pulse (generated by optical rectification of a 50fs optical pulse) will be used to spectrally time resolve the far-infrared transient response of high-TC superconductors induced by an optical pump pulse through the change in the reflectivity produced by the perturbed complex conductivity. Since the spectral extent of the linearly polarized THz probe pulse includes the superconducting gap 2A, this technique will be used to monitor directly the optically-induced perturbations to the anisotropic order parameter A, the pseudogap in under-doped materials, and transient inter- and intra-plane coupling between Cu-O layers and chains using untwinned Yttrium- and Barium-based cuprate crystals. In addition, to aid the understanding of the time-resolved THz spectra, two-photon excited-state angle-resolved photoemission spectroscopy will be employed to determine the relevant characteristics (lifetime and momentum) of the optically-coupled unoccupied states above the Fermi level. All measurements will be performed as a function of TITC to elucidate temperature dependencies. The results from these carefully designed ultrafast spectroscopic measurements should have a great impact on our understanding of the unique properties of high-TC superconductors in a manner parallel to that provided by similar femtosecond optical techniques in semiconductor physics. The educational component will involve both undergraduate physics majors and students from Chicago area high schools in research in the investigators laboratory that is connected to the goals of the project. %%% This is a CAREER Award which uses sophisticated optical methods to study high temperature superconductor s. The discovery in 1986 of copper-oxide-based ceramic materials, which exhibit zero electrical resistance at liquid nitrogen (-3 F) (rather than liquid helium (-450 F)) temperatures, has ignited technological interest in superconductivity as a means of dramatically reducing energy distribution costs, developing efficient high-speed levitating transportation, and making ultrafast electronic switches. However, despite a decade of exciting research into the properties of high-temperature superconductors (HTSCs), a definitive experiment leading to a clear understanding of the physical mechanism responsible for superconductivity in these unique materials has not been forthcoming. The goal of this research program is to exploit the sub-picosecond (shorter than one-thousand-billionth of a second) temporal resolution provided by today's laser technology to study the fundamental physical processes occurring in HTSCs. Specifically, ultrashort pulses of far-infrared radiation will be used to monitor the response of HTSCs in an effort to time-resolve the mechanism responsible for superconductivity in these ceramic materials. These ultrafast optical investigations will open a new regime of study for superconductivity in which radiation is used to monitor directly the electronic dynamics of the superconducting state. The results from these novel spectroscopic studies should have a significant impact on our understanding of the unique properties of HTSCs which, in turn, may lead to the development of superconductors operating at even higher temperatures. Indeed, similar ultrafast optical techniques have already improved our understanding and design of everyday semiconductor devices. The educational component will involve both undergraduate physics majors and students from Chicago area high schools in research in the investigators laboratory that is connected to the goals of the project. ***