By applying Hertzian stress fields up to $1.1\mathrm{kbar}$ along a (100) direction we break the cubic crystal symmetry of a cuprite crystal causing the triply degenerate orthoexciton level to split into a singlet and doublet. The interconversion rate between the singlet and lower-lying doublet is measured as a function of stress at $T=2\mathrm{K}$ by using subnanosecond time-resolved luminescence. Based on the experimentally observed stress dependence, we propose that this transition occurs via exciton and TA-phonon scattering associated with the off-diagonal shear tensor field (abbreviated “shear scattering”), in contrast to the axial vector field scattering (abbreviated “rotational scattering”) mechanism for the ortho-para conversion.

• Received 8 September 2005

DOI:https://doi.org/10.1103/PhysRevB.73.075207