Ultrafast spectroscopy of quantum materials

你的烤面包机让你的早餐面包发出嘎吱嘎吱的声音，让电流通过一圈电线，使线圈变红，让面包变成金黄色。导线变热是因为流经导线的电子流动不完美，在移动时撞到金属中的微小缺陷，将插座提供的电能转化为热能。同样的过程也导致了电力线和计算机芯片中不那么令人满意的电损耗。在典型的金属中，电子在撞上某物之前自由移动的平均时间是万亿分之一秒的几百万分之一秒，或几飞秒。为了感受这一时间单位的简洁性，一束光通过一根头发的宽度大约需要100飞秒。由这项研究拨款资助的实验将通过使用新技术产生持续时间为飞秒的激光脉冲，帮助我们了解抑制电子在材料中流动的过程。由于这些脉冲的长度与两次电子碰撞之间的平均时间相当，因此它们可以用来实时观察电子对电脉冲的响应。就像电影摄像机用一系列相隔30秒的静止照片来再现运动一样，我们可以进行一系列的电子测量，使用激光脉冲将观察时间限制在几飞秒。有了这些关于固体中电子运动的超高速电影，我们将能够更好地理解不同材料是如何导电的，以及哪些因素限制了这种导电。这些研究具有相当大的基础科学价值，加拿大研究人员因其对该领域知识的贡献而享誉国际。此外，这些研究提供的理解可能有助于我们设计用于电力线、消费电子和电子通信的电子材料。

Your toaster gives your morning bread its crunch by passing electrical current through a coil of wire, causing the wire to become red hot and your bread a golden brown. The wire heats up because the electrons flowing through it flow imperfectly, bumping into microscopic imperfections in the metal as they move, transforming the electrical energy supplied by your outlet into heat energy. The same process is responsible for the much less desirable electrical losses found in power lines and computer chips. In typical metals, the average time that an electron travels freely before bumping into something is a few millionths of a billionth of one second, or a few femtoseconds. For a sense of the brevity of this unit of time, it takes about one hundred femtoseconds for a beam of light to travel the width of a human hair. The experiments funded by this research grant will help us to understand the processes that inhibit the flow of electrons in materials, by employing new technology to generate laser pulses with femtosecond duration. Since these pulses are comparable in length to the average time between electron collisions, they can be used to observe the motion of electrons in real time as they respond to an electrical impulse. Much in the way a movie camera reproduces motion with a series of still photographs separated by a thirtieth of a second, we can make a series of electrical measurements, using the laser pulses to limit the time of observation to a few femtoseconds. Armed with these ultrafast movies of electronic motion in solids, we will be able to improve our understanding of how different materials conduct electricity, and what factors limit that conduction. These studies are of considerable basic scientific interest, and Canadian researchers are known internationally for our contributions to knowledge in this area. Furthermore, the understanding provided by these studies may help us to engineer electronic materials for use in power lines, consumer electronics and electronic communications.