Optical properties of exotic low-Tc superconductors

奇异低温超导体的光学特性

• 批准号: 155993-2010
• 负责人: Reedyk, Maureen
• 金额: $ 1.97万
• 依托单位: Brock University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2011
• 资助国家: 加拿大
• 起止时间: 2011-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=476118
• 关键词: Optical; properties; exotic; low; Tc

A superconductor is able to carry an electrical current with no energy losses when cooled below a `transition temperature', Tc. `Conventional' superconductors, such as an alloy of niobium and tin, are well understood and have been utilized for applications ranging from electronics to high field magnets used in medical scanners. One of the fundamental properties of a superconductor is that the electrons which carry the current exist in pairs. This differs from a `normal' metal where the electrons move independently. The atoms of a normal metal are arranged in a periodic structure called a `lattice'. Some negatively charged electrons `break-free' from each atom leaving positively charged `ions'. The electrons move about in this lattice of ions; the pairing resulting from an interaction between the lattice and the electrons. The energy required to break up one such pair of electrons, called the `energy gap', is an important parameter used to characterize superconductors. It is 1000 times less than the amount of energy contained in visible light and corresponds to radiation in a region of the electromagnetic spectrum called the far-infrared (FIR). FIR radiation incident on the sample with energy less than the energy-gap is reflected back, similar to the way visible light is reflected from a metallic surface. Measuring the energies which can and cannot be absorbed has contributed significantly to understanding how conventional superconductors work. There exist many less well-understood, `exotic' superconductors with very low Tc's. In many of these materials a magnetic phase transition occurs in the vicinity of, or even co-exists with the superconducting phase transition. This is thought to be important for understanding how the superconductivity arises. The response of these materials to light is expected to be very different from that of conventional superconductors. Herein we propose to investigate the optical properties of such low Tc superconductors; measurements that have not been carried out so far because they must be conducted at experimentally challenging low temperatures and energies that our apparatus is uniquely set-up to handle. We intend to extend the capabilities of our system to perform measurements in the presence of a magnetic field.

超导体在冷却到“转变温度”Tc以下时能够携带电流而没有能量损失。 “传统的”超导体，如铌和锡的合金，是众所周知的，并已被用于从电子到医疗扫描仪中使用的高场磁体的应用。 超导体的基本性质之一是携带电流的电子成对存在。这与电子独立运动的“正常”金属不同。 正常金属的原子排列成周期性结构，称为“晶格”。 一些带负电荷的电子从每个原子中“挣脱”出来，留下带正电荷的“离子”。 电子在这个离子晶格中移动;配对是晶格和电子之间相互作用的结果。分裂一对这样的电子所需的能量，称为“能隙”，是用来表征超导体的一个重要参数。 它比可见光所含的能量小1000倍，相当于电磁波谱中称为远红外（FIR）的区域的辐射。以小于能隙的能量入射到样品上的FIR辐射被反射回来，类似于可见光从金属表面反射的方式。 测量能被吸收和不能被吸收的能量对于理解传统超导体的工作原理有着重要的贡献。存在许多不太清楚的、具有很低Tc的“奇异”超导体。 在许多这些材料中，磁相变发生在超导相变附近，甚至与超导相变共存。 这对于理解超导性是如何产生的很重要。 这些材料对光的响应预计将与传统超导体非常不同。 在这里，我们建议研究这种低Tc超导体的光学特性;迄今为止尚未进行的测量，因为它们必须在实验上具有挑战性的低温和能量下进行，我们的设备是唯一设置来处理的。 我们打算扩展我们的系统的能力，在磁场的存在下进行测量。