Assignment of the Even-Parity Excitons inCu2O

Abstract
This Letter presents for the first time a detailed two-photon spectrum of the even-parity excitons of the yellow series in Cu2O. Contrary to one-photon data, it is possible to measure directly S and D exciton contributions without applying external perturbations. The two-photon spectrum gives evidence for a strong mixing between the yellow and the green series which is explained by exchange interaction and nondiagonal parts in the effective-mass Hamiltonian.