Unlocking ultrafast hot hole transport in transition metal oxides governed by the nature of optical transitions

Abstract

Abstract The intrinsically low carrier mobility of transition metal oxides within the polaron transport framework fundamentally limits their optoelectronic performance. Although optical transitions profoundly impact carrier generation and transport dynamics in oxide systems, the underlying mechanisms remain elusive. Here we demonstrate that the nature of optical transitions decisively regulates hot-hole transport in representative oxides, Co 3 O 4 and α-Fe 2 O 3 . Combining ultrafast optical nanoscopy with terahertz spectroscopy, we identify two distinct regimes: rapid band-like transport of energetic holes within a few picoseconds (~100 cm 2  s -1 ) and slower polaron-dominated hopping transport (~10 -3  cm 2  s -1 ) thereafter. Both the oxide composition and the transition pathway play critical roles in tailoring sub-picosecond hot-carrier dynamics. In Co 3 O 4 , metal-to-metal excitation at 1.55 eV yields an ultrahigh diffusion constant of 290 cm 2  s -1 , seven times that generated by higher-energy ligand-to-metal transitions (2.58 eV). These findings underscore the pivotal role of transient hot-carrier dynamics and suggest optical control of excited states as a promising route for optimizing energy management in oxide-based optoelectronic and photocatalytic systems.