Spin Lifetime Enhancement by External Magnetic Fields in Organometal Halide Perovskites

The organometal halide perovskites represent a new class of semiconductors that are solution processed but have excellent optoelectronic properties. Recent theories and experimental results suggest their exciting potential for spintronic applications as well. Specifically, theories have predicted giant Rashba effects, and our previous research revealed long spin lifetimes (>1 ns) in CH₃NH₃PbI₃, despite large spin-orbit coupling. Therefore, it is critical to understand the spin relaxation mechanisms. Here we study the hyperfine interaction contribution to spin relaxation by measuring time-resolved Faraday rotation in external magnetic fields. In transverse magnetic field, the spin lifetime T₂^* increases at low fields (<300 G) by up to 100%, and then decreases at higher fields due to spin dephasing. In longitudinal magnetic field, the spin lifetime T₁ increases up to a saturation value. The enhancement phenomena gradually disappear at temperatures above 40 K. A plausible picture is that this enhancement is due to the suppression of small random local effective magnetic fields induced by hyperfine interaction. We will present all the evidence supporting this hypothesis.