Speaker: Seamus O’Hara(University of Pennsylvania)

Host: Tom Iadecola

Title: The Optical Measurement of Hamiltonian Parameters in Driven Quantum Systems

Abstract: The study of quasiparticles in solids normally depends on the descriptions of interactions between the crystal lattice and quasiparticles on energy scales around the Fermi surface. The effective Hamiltonian of this system encapsulates these interactions and, through its eigenvalues, provides description of the energy landscape; through its eigenfunctions it provides a picture of the states which dominate the electrical and optical responses of the material at hand. As the world becomes more and more quantum, understanding and characterizing the parameters which compose the effective Hamiltonian through experimentation are taking on greater importance. In this talk, I will present an all-optical, non-equilibrium experiment, High-order Sideband Generation, which has been used to reconstruct various Hamiltonian parameters in bulk GaAs. I will discuss our results on measuring the effective band gap, dephasing rate, and Hamiltonian parameters and reconstructing the Bloch wavefunctions.

Biography: Seamus O’Hara is a Philadelphia native, having graduated from Springfield High School and The Pennsylvania State University, where he obtained bachelor's degrees in Physics and Mathematics. After Penn State, he went to the University of California, Santa Barbara to complete his PhD in Physics. While at UCSB, Seamus worked with Prof. Mark Sherwin, where he and a team of scientists at UCSB were the first to reconstruct the Bloch wave functions of electrons and holes in a semiconductor. Now, Seamus is building a THz/NIR system sensitive to the phases of exotic quasiparticles in quantum matter, working as an Intelligence Community Post-Doctroal Research Fellow under the guidance of Prof. Liang Wu at the University of Pennsylvania. Back home in Philadelphia, he enjoys runs and bike rides on the Schuylkill River Trail, going to Phillies games with his wife, Demi, and watching the Eagles win a Super Bowl (Go Birds!).