Ultrafast Dynamics of Iron-Based Superconductors

点击翻译按钮获取中文摘要

Nontechnical abstract: Recent discovery of high-temperature superconductivity in iron pnictides has initiated a new era in condensed matter physics, significantly expanding quantum materials research. The understanding of fundamental principles of light-matter interaction in iron-based superconductors on femto- pico- and nanosecond time scales contributes to new insight into the origin of High-T superconductivity. From a technological point of view, this knowledge is important for revolutionary applications of all-solid-state optical systems outside the laboratory because of their ruggedness, efficiency, compact size and ease of maintenance. The goal of this research is to obtain new information about transient dynamics of quasiparticles and nonequilibrium phases, carrier redistribution and relaxation, and ultrafast manipulation of electronic and structural order in iron-based superconductors. This knowledge is critical to build all-optical devices based on novel optical phenomena, and to create high-speed optoelectronic superconducting Q-bits which can operate at relatively high temperatures, above ~20 K. This project has significant institutional impact enhancing interdisciplinary advanced-level training for graduate and undergraduate Hispanic STEM students and postdoctoral researchers. The research activity integrates a broad spectrum of scientific, outreach and technical experiences, and most of the research is the part of the student/postdoctoral training on their ways to careers in academia and industry.Technical abstract: This project pursues experiments to elucidate the evolution of nonequilibrium phases of iron-based quantum materials, which is critical for understanding of fundamental dynamical processes of superconductivity upon photoexcitation. A variety of powerful femtosecond laser pump-probe spectroscopy techniques are applied to create and characterize novel quantum phases, quasiparticle relaxation and the electron-boson interactions. Methods of ultrafast optics provide stimulation and selective probing of specific degrees of freedom in solids in order to visualize multidimensional nonequilibrium dynamics on the timescale of lattice vibrations and to reveal dynamics of spontaneously broken symmetries, to elucidate hidden phases and features of light-induced suppression/creation of the superconducting state and to provide new insights into "intertwined" order parameters on ultrashort time scales. Real-time imaging of nonequilibrium dynamics across broad length and time scales can provide important information about the scales over which spin wave functions are coherent. To answer fundamental questions about the size-dependent quantum material dynamics, a novel time- and angle-resolved hemispherical light scattering method is applied. This technique visualizes angular distribution of scattered light at cryogenic temperatures to monitor transient nonequilibrium processes in grains/domains of different size. The fabrication of iron-based superconducting epitaxial films is based on new pulsed laser deposition protocols developed during the project.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.