Most of the parameters of the lowest excitons of Cu${}_2$O (1S excitons of yellow series) are very well known by now. After the experimental determination of the 1S paraexciton mass by two-phonon spectroscopy, a reliable parameter for the determination of orthoexciton masses is now available. Anisotropic mass values are expected for the threefold 1S orthoexciton, because of isotropic and anisotropic $k^2$ exchange terms. Taking into account the paraexciton mass ($2.61m_0$) instead of the previously used sum of bare band masses ($1.64m_0$), earlier orthoexciton mass values have to be revised. Again by two-phonon spectroscopy now of orthoexcitons the only unknown parameter ${\Delta }_1$ (isotropic $k^2$ exchange) is determined experimentally, which then allows a reliable determination of orthoexciton mass values in $\mathbf{k}$ space.

• Received 22 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.193205