Title: Photoinduced Hund excitons in the breakdown of a two-orbital Mott insulator,
Abstract: We study the photoinduced breakdown of a two-orbital Mott insulator and
resulting metallic state. Using time-dependent density matrix renormalization
group, we scrutinize the real-time dynamics of the half-filled two-orbital
Hubbard model interacting with a resonant radiation field pulse. The breakdown,
caused by production of doublon-holon pairs, is enhanced by Hund's exchange,
which dynamically activates large orbital fluctuations. The melting of the Mott
insulator is accompanied by a high to low spin transition with a concomitant
reduction of antiferromagnetic spin fluctuations. Most notably, the overall
time response is driven by the photogeneration of excitons with orbital
character that are stabilized by Hund's coupling. These unconventional "Hund
excitons" correspond to bound spin-singlet orbital-triplet doublon-holon pairs.
We study exciton properties such as bandwidth, binding potential, and size
within a semiclassical approach. The photometallic state results from a
coexistence of Hund excitons and doublon-holon plasma.