Electrodynamics of topological and quantum materials

量子力学发明后不久，像爱因斯坦这样的物理学家开始应用它来理解固体的性质。通常我们把量子力学和小东西联系在一起，比如原子或亚原子粒子。但固体的量子理论是20世纪最伟大的智力成就之一，它使晶体管、半导体激光器和高密度磁存储器的发明成为可能，从而改变了社会。然而，尽管我们掌握了所有的知识，研究这些东西的物理学家仍然会遇到各种各样的现象，这些现象对教科书中的理论提出了根本性的挑战。在某些材料中，电子可以通过它们的相互排斥来阻止导电，这会导致它们被卡住，就像量子停车场里的汽车;在另一些材料中，电子自发地自组织排列，导致整个材料的对称性发生变化;还有一些是在表面被薄金属片包裹的电绝缘体，其被称为“拓扑绝缘体”，因为其占用的空间超过了所允许的空间。 所有这些都代表了我们目前理解的前沿，为了强调这种统一性，加拿大研究人员创造了量子材料一词来描述它们。量子材料的研究是当代固体研究中的一个重要课题。就像早期对固态的研究一样，它有望推进我们对物质的理解，扩大我们设计新电子材料的能力，为未来技术奠定基础，因为它加深了我们对自然的理解。我们可以问的关于固体的最基本的问题之一是它如何对光做出反应，因此光学在这项研究中起着重要的作用。我们可以看到电绝缘体（如玻璃）和金属（如铝）之间的区别，只要看它们。通过将其扩展到可见光以外的波长，我们在实验光谱学方面的研究使我们能够比我们的眼睛看到更多关于固体的信息。我的研究计划的目标是利用现代激光器研究量子材料的研究。我们可以使用可见波长的脉冲激光来产生远红外光，称为太赫兹波，我们可以用它来区分超导体和金属之间的区别。利用激光器发出的强烈偏振光，我们可以以极高的灵敏度识别固体的许多基本对称性，这进一步使我们能够检测如果电子自发自组织，这些对称性如何变化。通过强烈的光脉冲，我们还可以改变固体，观察它们的演变，使它们脱离平衡，然后描述它们如何恢复到原始状态，或者将它们推入一个完全不同的状态。通过这些技术，我们的目标是更深入地了解量子材料，以便有一天我们可以像使用硅一样使用它们。

Soon after quantum mechanics was invented, physicists like Einstein began to apply it to understand the properties of solids. Normally we associate quantum mechanics with small things, like atoms or subatomic particles. But the quantum theory of solids is one of the great intellectual achievements of the twentieth century, and has transformed society by enabling the invention of the transistor, the semiconductor laser, and high-density magnetic storage. Yet for all our know-how, physicists who study these things still encounter a variety of phenomena that present fundamental challenges to the theories found in textbooks. In some materials, electrons can be prevented from conducting electricity by their mutual repulsion, which causes them to get stuck, like cars in a quantum parking lot; in others, the electrons spontaneously self-organize in arrangements that cause the symmetry of the whole material to change; still others are electrical insulators that are encased by a thin metallic sheet at the surface, which have been dubbed “topological insulators” for reasons that take more than this space allows. All of them represent frontiers of our current understanding, and to emphasize this unity, Canadian researchers coined the term quantum materials to describe them. Research on quantum materials is now a dominant theme in contemporary research on solids. Like earlier research on the solid state, it promises to both advance our understanding of matter and expand our capacity to engineer new electronic materials, laying the foundation for future technology as it deepens our appreciation of nature. One of the most basic questions we can ask about a solid is how it responds to light, so optics plays an important role in this research. We can see the difference between an electrical insulator, such as glass, and a metal, such as aluminum, just by looking at them. By extending this to wavelengths beyond the visible, our research in experimental optical spectroscopy allows us to see more about the solid than we could with our eyes. The goal of my research program is to exploit modern lasers in research on quantum materials research. We can use pulsed lasers at visible wavelengths to generate far-infrared light, known as terahertz waves, which we can use to readily tell the difference between a superconductor and a metal. With intense polarized light from a laser we can identify many of the fundamental symmetries of solids with exquisite sensitivity, which further allows us to detect how these symmetries change if the electrons spontaneously self-organize. And with intense bursts of light we can also change solids and watch them evolve, exciting them out of equilibrium and then characterizing how they return to their original state, or pushing them into an altogether different one. Through these techniques, we aim to understand quantum materials more deeply, so that someday we might put them to use as we have with silicon.