Piezospectroscopic investigation of the nature of the subsidiary valence band extrema in TiO2

In order to assess the localization in k-space of the secondary valence band extrema, we have measured the stress dependence of the indirect transition of TiO₂, at 1.6 K, for static uniaxial compression along the 100] and 110] directions. From the stress-induced splittings we localize the secondary valence-band extrema in 100] direction (Δ direction) and associate the indirect gap of TiO₂ with a Δ_4v → Γ_1c phonon-assisted transition. The shear deformation potential of the Δ_4v valence band has been determined from the stress-induced splitting of the TA phonon-assited transition. We find |C_Δ4v| = 0.75 eV.