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

非技术摘要：该项目在太阳能电池、发光二极管和激光等各种设想的技术背景下，研究一种有前途的半导体材料，称为有机-无机钙钛矿混合体，在与光相互作用时的性质。构成这些材料的原子产生了相当“不稳定”的晶格，在这种晶格中，相互连接的原子在环境条件下的运动是剧烈的。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，彼此之间相互作用很强，而且是稳定的。一个类比是，在一场高震级地震中，一组完美编排的多名舞者以完美的舞蹈编排。关于这些粒子如何相互作用以及相互作用多长时间的细节，在这个项目中至关重要。为了研究这些细节，佐治亚理工学院的研究人员将开发基于产生非常短的光脉冲(飞秒，短于十亿分之一秒)的激光的实验方法，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这些实验。这些合作活动将导致对这些激子半导体的基本材料物理的新的理解，这将促进用于固态照明和激光的光电子器件的下一个重大突破。技术摘要：这个合作项目将开发一种相干的二维(2D)光激发光谱，优化用于探测在功能光电器件中实现的半导体材料中的多粒子关联。该技术基于四个可变延迟的超短激光脉冲序列的相位调制，以及对由该脉冲序列感应的光电流的相敏检测。这允许通过隔离对光电流激励信号的特定非线性贡献来获取2D相干光谱。这一方法之前已经被几位研究人员实施过。最近的研究表明，在整个光激发寿命中，由非线性布居动力学引起的对测量线形的非相干贡献，在许多凝聚相系统中产生了与预期的2D相干谱相似的线形，其中光激发具有足够的移动性，使得粒子间的相互作用在任何时间尺度上都是重要的，包括那些与2D相干实验相比更长的时间尺度。合作研究人员提出了一种克服这一限制的外差探测方案，并将利用这项技术来研究二维、量子井状有机-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关联。具体目标是：(1)发展一种用于光电流检测的二维相干多激发光谱的外差检测方案，并在高效的砷化镓光电探测器、优化的甲基碘化铅钙钛矿型太阳电池和苯乙基乙基碘化铅-二维钙钛矿发光二极管中进行演示；(Ii)开发基于相同探测方案的多量子2D变体，并研究上述2D钙钛矿设备中的多激子和三子，以及(Iii)基于参数格子哈密顿量开发可访问的、基于参数格子哈密顿量的2D相干激发光谱的通用建模协议，该协议将早期的非马尔科夫动力学与时间积分响应联系起来。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.