Terahertz Recollisions

非技术摘要高能物理学家通过质子和电子等基本粒子的碰撞来探索物质的结构。在固体中，电流--比如被阳光照射后在光伏电池中产生的电流--通常由被称为“准粒子”的实体携带。当受到力的作用时，准粒子的行为就像粒子，但实际上涉及数千到数百万个原子的协调运动。如果固体中的一个原子被放大到一个人的大小，那么一个准粒子看起来就像一个巨大的、满的体育场里的“波”。PI的团队最近发现了一种方法，可以每秒加速和碰撞准粒子约1万亿次(1太赫兹)。准粒子碰撞的实验特征是一种彩虹状的光谱，其中包含数十个频率或边带，这些频率或边带像梳子上的牙齿一样均匀分布。每个边带都携带着关于准粒子碰撞速度的信息，以及它们在碰撞前被加速通过的固体的量子力学性质。在这个项目中，PI的团队将仔细分析各种电子材料的边带强度和极化，以阐明控制准粒子运动的规律，并寻找强驱动物质的新相。拟议研究的可能应用包括更快、更节能的光通信和互联网，改进全球定位系统所需的光钟，以及快速和可逆地调整材料特性的能力。该项目将支持两名博士生和几名本科生的培训，他们将学习各种技能，这些技能对于保持美国在高科技领域的竞争力至关重要。技术摘要该项目解决了21世纪科学的重大挑战之一--当量子物质远离热平衡时，它的行为如何。该项目的目标是利用强驱动物质研究中的新机会：(1)开发一种测量固体中能带的Berry曲率的方法，这对于理解准粒子的动力学至关重要；(2)阐明电子之间的相关性很强的材料中准粒子的性质，如高T_c超导体的母体化合物；以及(3)在受强时间周期场驱动的材料边缘附近寻找新的量子力学相。为了达到这些目标，本项目将利用PI小组最近发现的高阶边带产生(HSG)。当每种感兴趣的材料被太赫兹频率的强电场驱动时，它将被近红外激光照射，并将分析产生的HSG光谱的强度和偏振。实验将与理论紧密结合，以达到项目目标。

Nontechnical AbstractHigh-energy physicists explore the structure of matter by colliding elementary particles like protons and electrons. In solids, currents--like those generated in a photovoltaic cell after illumination by sunlight--are usually carried by entities called "quasi-particles." When acted on by a force, quasi-particles behave like particles, but actually involve the co-ordinated motions of thousands to millions of atoms. If an atom in a solid were scaled up to be the size of a person, then a quasi-particle would look something like "the wave" in a large, full stadium. The PI's group has recently discovered a method to accelerate and collide quasi-particles about 1 trillion times per second (1 Terahertz). The experimental signature of quasi-particle collisions is a rainbow-like spectrum of light that contains dozens of frequencies, or sidebands, that are equally spaced like the teeth on a comb. Each sideband, carries information about the speed with which the quasiparticles have collided, and the quantum-mechanical properties of the solid through which they have been accelerated before colliding. In this project, the PI's group will carefully analyze both the intensities and polarizations of the sidebands from a variety of electronic materials in order to elucidate the laws that govern the motion of quasiparticles and to search for new phases of strongly-driven matter. Possible applications of the proposed research include faster and more energy efficient optical communications and internet, improved optical clocks that are necessary in the global positioning system, and the ability to rapidly and reversibly tune the properties of materials. This project will support the training of two Ph. D. students and several undergraduates, who will learn a variety of skills that are critical to preserving U. S. competitiveness in the high-technology sector.Technical AbstractThis project addresses one of the grand challenges of 21st century science--how does quantum matter behave when it is driven very far from thermal equilibrium. The goals of this project are to take advantage of new opportunities in the study of strongly-driven matter to (1) develop a method of measuring the Berry curvature of bands in solids, which is critical to understanding the dynamics of quasiparticles; (2) elucidate the nature of quasiparticles in materials in which correlations between electrons are strong, like the parent compounds of high-Tc superconductors; and (3) search for new quantum-mechanical phases near the edges of materials that are driven by strong, time-periodic fields. In order to reach these goals, this project will use the recent discovery of high-order sideband generation (HSG) by the PI's group. Each of the materials of interest will be illuminated by a NIR laser while it is being driven by a strong THz-frequency electric field, and the intensities and polarizations of the resulting HSG spectra will be analyzed. Experiments will be closely coupled with theory to reach the project goals.