Exciton Control in a Room-Temperature Bulk Semiconductor with Coherent Strain Pulses

TL;DR

This study demonstrates the control of excitons in bulk TiO₂ using coherent strain pulses at room temperature, revealing significant exciton modulation and shifts, which could enable new deep-ultraviolet optoelectronic devices.

Contribution

It introduces a method for ultrafast exciton control in bulk wide-bandgap semiconductors using coherent acoustic phonons at room temperature.

Findings

Giant exciton shift of 30-50 meV observed

Strong modulation of exciton peak amplitude

Deformation potential coupling identified as main mechanism

Abstract

The coherent manipulation of excitons in bulk semiconductors via the lattice degrees of freedom is key to the development of acousto-optic and acousto-excitonic devices. Wide-bandgap transition metal oxides exhibit strongly bound excitons that are interesting for applications in the deep-ultraviolet, but their properties have remained elusive due to the lack of efficient generation and detection schemes in this spectral range. Here, we perform ultrafast broadband deep-ultraviolet spectroscopy on anatase TiO$_2$ single crystals at room temperature, and reveal a dramatic modulation of the exciton peak amplitude due to coherent acoustic phonons. This modulation is comparable to those of nanostructures where exciton-phonon coupling is enhanced by quantum confinement, and is accompanied by a giant exciton shift of 30-50 meV. We model these results by many-body perturbation theory and show that the deformation potential coupling within the nonlinear regime is the main mechanism for the generation and detection of the coherent acoustic phonons. Our findings pave the way to the design of exciton control schemes in the deep-ultraviolet with propagating strain pulses.