Bloch wave interferometry in semiconductors and correlated insulators

非技术描述：为了满足社会对信息技术的未来需求，需要不断加强对半导体材料和光的控制，半导体材料是制造电子产品的材料，而光可以以不断增长的速度传输大量信息。量子力学告诉我们半导体中的电子应该表现得像波。对这些电子波的详细了解是设计下一代电子和光学设备所必需的。最近，利用一种强大的、建筑物大小的激光器快速加速半导体中的电荷，并在它们与其他任何东西相撞之前将它们撞回一起，首席研究员小组已经能够观察到两种加速的电子波相互干扰，类似于扔进池塘的两块石头所产生的涟漪。根据干扰的模式，主要研究者小组第一次能够直接从实验数据中重建半导体中干扰电子波的数学形式。在这个项目中，研究小组利用电子波的干扰来开发一种方法来精确测量控制半导体中电荷运动和光的吸收和发射的重要参数。这项研究是由研究生和本科生研究人员进行的，在这个过程中，他们在半导体物理、光学方面接受了严格的训练，最重要的是，解决了以前从未解决过的难题。通过这些培训，这些研究人员将很好地为工业、学术界或政府发展未来的信息技术做出贡献。这些研究人员还参与了PI的流行教育推广计划，自2005年以来，该计划在当地社区科学之夜为K-12学生带来了吸引人的、引人入胜的、强大的“问答板”，让他们亲身体验电路。技术描述：干涉测量是一种强大的工具，用于测量各种波中编码的信息。固体中的带电准粒子具有波状特征，这在它们的布洛赫波函数中可以捕捉到。2011年，主要研究者小组报告了高阶边带生成的实验发现，在弱近红外激光和强太赫兹激光同时驱动的半导体中，可以在梳状光谱中发射几十个近红外边带，梳齿之间的间隔是太赫兹频率的整数倍。最近，该小组报告说，大块砷化镓（GaAs）发射的边带偏振可以看作是布洛赫波的迈克尔逊干涉仪的干涉图，并使用简单的分析模型进行计算。本项目采用定量布洛赫波干涉法，从三个方面进行了研究：(1)重建体GaAs中电子-空穴对的有效哈密顿量、精确带隙和去相过程。这将为技术关键的直接间隙半导体中更精确的电子结构测量打开大门；(2)测量由极大价带Berry曲率引起的GaAs量子阱中空穴的异常位移（横向于加速电场方向）。这将是对异常速度最清晰的证明之一——近70年前首次被预测到——并可能使对波段的局部贝里曲率的直接测量成为可能；(3)将布洛赫波干涉测量法扩展到莫特绝缘体，从范德华反铁磁体NiPS3开始，打开一个新的窗口，了解强相关绝缘体的电子结构，因为它的激子非常明亮和狭窄。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical description:Meeting society’s future demands for information technology requires ever-increasing control over semiconducting materials, from which electronics are made, and light, which transmits vast quantities of information at continually-increasing speeds. Quantum mechanics tells us that electrons in semiconductors should behave like waves. A detailed understanding of these electronic waves is required to engineer the next generations of electronic and optical devices. Recently, using a powerful, building-sized laser to rapidly accelerate charges in a semiconductor and smash them back together before they can collide with anything else, the principle investigator’s group has been able to observe two kinds of accelerated electronic waves interfering with one another, analogous to the interaction of ripples from two stones thrown into a pond. From the pattern of the interference, the principle investigator’s group has been able, for the first time, to reconstruct directly from experimental data the mathematical form of interfering electronic waves in a semiconductor. In this project, the research team leverages the interference of electronic waves to develop a method to precisely measure important parameters that govern both the motion of charges in and the absorption and emission of light from semiconductors. The research is carried out by graduate and undergraduate student researchers who, in the process, get rigorous training in semiconductor physics, optics, and, most importantly, solving hard problems that have never been solved before. With this training, these researchers will be well-positioned to contribute to developing future information technologies in industry, academia, or government. These researchers also participate in the PI’s popular educational outreach program that has, since 2005, brought attractive, engaging and robust "Questboards" to local community science nights for K-12 students to get hands-on experience with electrical circuits.Technical description:Interferometry is a powerful tool for measuring information encoded in waves of all sorts. Charged quasiparticles in solids have a wavelike character that is captured in their Bloch wavefunctions. In 2011, the principle investigator’s group reported the experimental discovery of high-order sideband generation, in which a semiconductor driven simultaneously by a weak near-infrared laser and a strong THz laser can emit many dozen near-infrared sidebands in a comb-like spectrum with comb teeth separated by an integer multiple of the THz frequency. Recently, the group reported that the polarizations of sidebands emitted from bulk gallium arsenide (GaAs) can be viewed as interferograms from a Michelson-like interferometer for Bloch waves, and calculated using a simple analytical model. This project uses quantitative Bloch-wave interferometry in three ways: (1) reconstruct the effective Hamiltonian, precise band gaps, and de-phasing processes of electron-hole pairs in bulk GaAs. This will open the door to much more precise electronic structure measurements in the technologically-critical direct-gap semiconductors; (2) measure anomalous displacements (transverse to the direction of the accelerating electric field) of holes in GaAs quantum wells caused by extremely large valence band Berry curvatures. This will be among the cleanest demonstrations of anomalous velocity—first predicted nearly 70 years ago—and may enable a direct measurement of the local Berry curvature of a band; (3) extend Bloch-wave interferometry to Mott insulators, beginning with the van der Waals antiferromagnet NiPS3, a promising candidate because of its extremely bright and narrow exciton, opening a new window into the electronic structure of strongly-correlated insulators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.