Short Time Dynamics of Photoexcited Carriers of Methylammonium Lead Iodide Perovskites at Room Temperature  (Maria Muñoz)

Abstract:

Since the rise of the concept of quantum materials (QM), these materials described as many-body quantum systems (interacting atoms, molecules, or electrons) have been suitable for many optoelectronic and quantum applications. Additionally, there has been significant interest in the research of QM to understand underlying physics behind their extraordinary optical properties. Examples of QM are ultracold atoms, layered 2D semiconductors, supramolecular materials, and more. In 2012, a high energy conversion efficiency over 10% was reported for the first time, for metal-halide perovskite (MHP) solar cells, opening a new era for photovoltaics research. The reported efficiencies have been improved to 22.7%, over the years. Additionally, these exceptional semiconductor MHP materials are also promising candidates for the new generation of optoelectronics. This research focuses on the study of many-body interactions and their dynamics of methylammonium lead iodide (MAPI) CH₃NH₃PbI₃ thin film materials at room temperature.

In this work, Maria Muñoz utilized cutting-edge optical spectroscopies techniques to study ultrafast dynamics of photoexcited electron-holes pairs in MAPI perovskites films. She first performed steady-state spectroscopic measurements to characterize the sample, then implemented optical 2D coherent spectroscopy in the nonlinear geometry to probe the ultrafast dynamics. Her experiment revealed many-body couplings and ultrafast dynamics of free-carrier and exciton resonances that coexist for a few hundreds of femtoseconds. The data revealed the charge-carrier relaxation dynamics after the excitation of the sample in terms of thermalization, cooling, exciton dissociation, and many-body effects. Furthermore, those dynamics showed dependance on the excitation control variables, such as wavelength excitation and photoexcited carrier density generated.

Short Range Quark-Quark Interactions and Nucleon Structure Function at High Bjorken x (Joseph Maerovitz)

Abstract:

We are studying the nucleon structure using QCD and the interior interactions. We model the nucleon as a valence quark system and a residual system. We model the valence quark momentum distribution and structure function using three mechanisms: mean field, two quark short range correlations and, three quark short range correlations calculated by Light Front Diagrammatic methods in leading order approximation. The previous study of the mean field model set the parameters of the short-range correlations which happens at higher momentum fraction x. The short-range correlations of the valence quarks emit hard gluon exchanges. In the calculation we considered both two- and three-quark short range interactions through hard gluon exchange which are calculated within perturbative QCD.