Ultrafast spectroscopy of quantum materials

你的烤面包机让电流通过一圈电线，使电线变红变热，面包变成金棕色，从而使早晨的面包嘎吱作响。电线受热是因为流过它的电子不完美地流动，在移动时撞到金属的微小缺陷，将插座提供的电能转化为热能。在电力线和计算机芯片中，同样的过程也造成了不太理想的电损耗。在典型的金属中，电子在撞到物体之前自由移动的平均时间是十亿分之一秒的百万分之几，或者几飞秒。为了感受这个时间单位的短暂性，一束光穿过一根头发的宽度大约需要100飞秒。这项研究资助的实验将通过采用新技术产生飞秒持续时间的激光脉冲，帮助我们了解抑制材料中电子流动的过程。由于这些脉冲的长度与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反应。就像电影摄影机用相隔三十分之一秒的一系列静止照片再现运动一样，我们可以利用激光脉冲将观察时间限制在几飞秒内，进行一系列的电子测量。有了这些固体中电子运动的超快电影，我们将能够提高我们对不同材料如何导电的理解，以及什么因素限制了导电。这些研究具有相当大的基础科学兴趣，加拿大研究人员因在这一领域的知识贡献而享誉国际。此外，这些研究提供的理解可以帮助我们设计用于电力线，消费电子产品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.