Nathan Gundlach Friday, May 4, 2018 at 3 PM (110 INSCC)
Title: Ultrafast Optical Study of Spin Dynamics in Hybrid Perovskite Semiconductors
The field of semiconductor spintronics aims to expand the capabilities of conventional electronics by making use of the spin degree of freedom of electrons. While many device concepts have been proposed, it remains a big challenge to find both long spin lifetime and an effective means of spin manipulation in the semiconductor. My graduate research demonstrates that hybrid organic-inorganic perovskite semiconductors may be a promising class of candidate materials for spintronic applications due to their large and tunable spin-orbit coupling, spin-dependent optical selection rules, and long carrier lifetimes.
Here I present results demonstrating optical orientation of exciton spins and optical detection of spin-polarized quantum beating between exciton states in polycrystalline films of methylammonium lead iodide perovskite. Using time-resolved Faraday rotation measurements, we observe surprisingly long spin lifetimes, despite large spin-orbit coupling. By applying a transverse external magnetic field, we observe quantum beating between exciton states as oscillations in the Faraday rotation with two distinct frequencies, from which we extract g-factors corresponding to electrons and holes, based on an effective-mass model.
To better understand the spin relaxation mechanisms at work in our material, we examine the effects of the hyperfine interaction between carriers and nuclei on spin lifetime. Application of a small external magnetic field suppresses the random nuclear magnetic fields and enhances spin lifetime.
These results demonstrate that optical methods are a useful tool for studying spin properties in hybrid perovskite materials, and provide a basic picture of the spin dynamics.