Collaborative Research: Unraveling Many-body Correlations in Two-dimensional Hybrid Semiconductors

非技术摘要：该项目解决了一种有前途的半导体材料，称为混合有机-无机钙钛矿，在与光相互作用时，在各种设想的技术，如太阳能电池，发光二极管和激光器的背景下的性能。构成这些材料的原子产生基本上“不稳定的”晶格，其中在环境条件下相互连接的原子的运动是剧烈的。尽管有这种高度动态的环境，但与光相互作用产生的粒子，即所谓的激子，彼此之间强烈相互作用并且是稳定的。一个类比是，在一场高震级的地震中，一组完美的舞蹈演员在完美的舞蹈中表演。关于这些粒子如何相互作用以及相互作用的时间长短的细节在这个项目中至关重要。为了研究这些细节，格鲁吉亚理工学院的研究人员将开发基于激光产生非常短的光脉冲（飞秒，短于十亿分之一秒的百万分之一）的实验方法，以选择性地研究它们作为时间函数的相互作用。与此同时，休斯顿大学的研究人员将开发理论技术来模拟实验。这些合作活动将导致这些激子半导体的基本材料物理学的新的理解，这将促进下一个重大突破，在光电器件的固态照明和laser.Technical摘要：这个合作项目将开发一个相干的二维（2D）光激发光谱优化探测多粒子相关性的半导体材料中实现的功能光电器件。该技术是基于相位调制的一个序列的四个延迟的超短激光脉冲，和相敏检测的光电流所引起的脉冲序列。这允许通过隔离对光电流激发信号的特定非线性贡献来获取2D相干光谱。这种方法以前已经由几位研究人员实施。最近，它被证明是一个不相干的贡献所测量的线形，所产生的非线性人口动力学在整个光激发寿命，在许多凝聚相系统，其中光激发是足够的移动的，使粒子间的相互作用是重要的任何时间尺度上，包括那些长的2D相干实验相比，预期的2D相干光谱产生类似的线形。合作研究人员提出了一种克服这一限制的外差检测方案，并将利用该技术研究二维量子阱混合有机-无机金属卤化物钙钛矿中涉及激子和电荷载流子的多粒子相关性。具体目标是（i）开发用于光电流检测的2D相干多激发光谱的外差检测协议，并在高效GaAs光电检测器、优化的甲基铵碘化铅钙钛矿太阳能电池和苯基乙基铵碘化铅2D钙钛矿发光二极管中证明该协议;（ii）开发基于相同检测方案的多量子2D变体，并研究上述2D钙钛矿器件中的多激子和三电子，以及（iii）开发可访问的，基于参数化晶格哈密顿量的光电流检测二维相干激发光谱的通用建模协议，它将早期的非马尔可夫动力学与时间联系起来，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

Non-technical Abstract:This project addresses the properties of a promising kind of semiconductor material, called hybrid organic-inorganic perovskites, upon interaction with light, in the context of a variety of envisioned technologies such as solar cells, light-emitting diodes, and lasers. The atoms that constitute these materials produce substantially "shaky" crystal lattices, in which at ambient conditions the motion of interconnected atoms is vigorous. In spite of this highly dynamic environment, particles that arise from interaction with light, so-called excitons, interact amongst each other strongly and are stable. An analogy would be that of a perfectly choreographed set of multiple dancers in perfect choreography during a high-magnitude earthquake. The details on how and for how long these particles interact is of central importance in this project. To study these details, researchers at Georgia Tech will develop experimental methods based on lasers producing very short bursts of light (femtoseconds, shorter than amillionth of a billionth of a second) to study selectively their mutual interactions as a function of time. In parallel, researchers at the University of Houston will develop theoretical techniques to model the experiments. These collaborative activities will result in new understanding of the fundamental materials physics of these exciton semiconductors, which will facilitate the next significant breakthroughs in optoelectronic devices for solid-state lighting and lasers.Technical Abstract:This collaborative project will develop a coherent two-dimensional (2D) photoexcitation spectroscopy optimized to probe multi-particle correlations in semiconductor materials implemented in functional optoelectronic devices. The technique is based on phase modulation of a sequence of four variably delayed ultrashort laser pulses, and phase-sensitive detection of the photocurrent induced by that pulse sequence. This permits acquisition of 2D coherent spectra by isolating specific nonlinear contributions to the photocurrent excitation signal. This methodology has been previously implemented by several researchers. Recently it was demonstrated that an incoherent contribution to the measured line shape, arising from nonlinear population dynamics over the entire photoexcitation lifetime, generates a similar line shape to the expected 2D coherent spectra in many condensed-phase systems, in which photoexcitations are sufficiently mobile such that inter-particle interactions are important on any time scale, including those long compared with the 2D coherent experiment. The co-investigators propose a heterodyne detection scheme that surmounts this limitation, and will exploit the technique to study multi-particle correlations involving excitons and charge-carriers in two-dimensional, quantum-well-like hybrid organic-inorganic metal-halide perovskites. The specific objectives are (i) to develop a heterodyne detection protocol for photocurrent-detected 2D coherent multiexcitation spectroscopy and to demonstrate it in a highly efficient GaAs photodetector, in an optimized methylammonium lead-iodide perovskite solar cell, and in a phenylethylammonium lead-iodide 2D perovskite light-emitting diode; (ii) to develop a multiquantum 2D variant based on the same detection scheme and to study multi-excitons and trions in the 2D perovskite device above, and (iii) to develop an accessible, general modeling protocol for the photocurrent-detected 2D coherent excitation spectra based on parametrized lattice Hamiltonians, which connects early-time non-Markovian dynamics with the time-integrated response.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.