  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.
