Creation of Nonthermal Excited State Populations in a Large U Mott Insulator

The ability to tune between thermal and nonthermal populations lies at the heart at the heart of quantum control on ultrafast timescales. In this work, we perform time-and-angle resolved spectroscopy on the spin-orbit assisted Mott insulator α-RuCl₃. We demonstrate the ability to tune between thermalized and nonthermalized populations in the upper Hubbard band by tuning the pump energy. These populations are also shown to thermalize and decay on timescales much faster than those predicted by theory.