Precision Measurement of the Infrared Reflectance of High-TcSuperconducting Films

高温超导薄膜红外反射率的精密测量

• 批准号: 9007765
• 负责人: Markus Flik
• 金额: --
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-09-01 至 1992-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9007765&HistoricalAwards=false
• 关键词: Precision; Measurement; Infrared; Reflectance; TcSuperconducting

There is great current interest in the infrared radiative properties of high-Tc superconducting films and crystals. This interest stems from both fundamental considerations and promising applications. One promising application of high-Tc superconducting films is as infrared radiation detectors. It has also been proposed to cool superconducting electronics for space applications passively by thermal radiation. If the high-Tc superconductors are perfect reflectors at wavelengths greater than that corresponding to the energy gap, then a high-Tc superconductor radiation shield would show excellent performance if kept at a temperature of 20 K. Precise knowledge of optical properties, and particularly the complex refractive indices of high-Tc superconducting films, are required to evaluate these applications. In this study the monochromatic normal reflectance of high- quality films of YBaCuO and BiSrCaCuO is being measured with sets of four identical samples for temperatures between 6 K and room temperature, at wavelengths from 0.5 um to 30 um. The measurements are performed with a high-precision grating spectrometer which was especially designed for the measurement of the low-temperature radiative properties of noble-metal films. This apparatus does not employ a reference mirror. For the background measurement, the infrared beam travels through the sample compartment without optical interaction. The reflectance data are obtained by passing the beam through eight reflections from four identical samples. This technique avoids both shortcomings associated with the reference-mirror single-reflection method. Due to the absence of a mirror, absolute reflectance data are obtained, not values relative to a mirror reflectance less than unity. The measurements are carried out with films of the highest quality available, fabricated by Siemens, Erlangen, West Germany, and the IBM T.J. Watson Research Center, Yorktown Heights. These films are of pseudocrystalline nature, with strong c axis upward orientation, such that the radiative properties of the ab plane of the crystal unit cell are measured. These measurements are expected to set a new standard for the high- Tc materials. This standard will help to clarify the applicability of BCS-based theories to the optical properties of superconducting high-Tc films. The new precision measurements are also expected to shed light on the problem of the energy gap as observed by infrared spectra.

目前人们对高温超导薄膜和晶体的红外辐射特性有很大的兴趣。这种兴趣源于基本的考虑和有前途的应用。高温超导薄膜的一个很有前途的应用是作为红外辐射探测器。也有人提出通过热辐射被动冷却超导电子设备用于空间应用。如果高tc超导体在大于对应能隙的波长上是完美的反射体，那么在20 K的温度下，高tc超导体辐射屏蔽将表现出优异的性能。评估这些应用需要精确的光学特性知识，特别是高tc超导薄膜的复折射率。在这项研究中，在6 K和室温之间，波长从0.5 um到30 um之间，用四组相同的样品测量了高质量YBaCuO和BiSrCaCuO薄膜的单色正反射率。采用高精度光栅光谱仪进行测量，该光谱仪是专门为测量贵金属薄膜的低温辐射特性而设计的。这个装置不使用参考镜。对于背景测量，红外光束在没有光相互作用的情况下穿过样品室。反射率数据是通过光束通过四个相同样品的八个反射来获得的。这种技术避免了与参考镜单反射方法相关的两个缺点。由于没有镜面，获得的是绝对反射率数据，而不是相对于镜面反射率小于1的值。测量是用最高质量的薄膜进行的，由西德埃尔兰根的西门子公司和约克镇高地的IBM T.J.沃森研究中心制造。这些薄膜具有伪晶性质，具有很强的c轴向上取向，因此可以测量晶体单元胞ab平面的辐射特性。这些测量结果有望为高Tc材料设定一个新的标准。本标准将有助于阐明基于bcs的理论对超导高tc薄膜光学性质的适用性。新的精密测量也有望阐明红外光谱观测到的能隙问题。