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

## TL;DR

The study shows how optical transitions control hot-hole transport in transition metal oxides, revealing fast and slow transport regimes that could improve optoelectronic and photocatalytic devices.

## Contribution

The study identifies how optical transition pathways govern ultrafast hot-hole transport in transition metal oxides, revealing distinct transport regimes.

## Key findings

- Ultrafast band-like transport of energetic holes occurs within picoseconds in transition metal oxides.
- Metal-to-metal excitation in Co3O4 produces an ultrahigh diffusion constant seven times higher than ligand-to-metal transitions.
- Optical transitions and oxide composition critically influence sub-picosecond hot-carrier dynamics.

## 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, Co3O4 and α-Fe2O3. Combining ultrafast optical nanoscopy with terahertz spectroscopy, we identify two distinct regimes: rapid band-like transport of energetic holes within a few picoseconds (~100 cm2 s-1) and slower polaron-dominated hopping transport (~10-3 cm2 s-1) thereafter. Both the oxide composition and the transition pathway play critical roles in tailoring sub-picosecond hot-carrier dynamics. In Co3O4, metal-to-metal excitation at 1.55 eV yields an ultrahigh diffusion constant of 290 cm2 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.

This study reveals how the nature of optical excitation governs hot-carrier transport in transition metal oxides and directly visualizes distinct transport regimes via high spatiotemporal resolution imaging.