Infrared absorption by excitons in Cu2O

In a differential absorption experiment the induced infrared transitions from the excitonic 1s to the 2p levels in Cu 2 O have been investigated. Intermediate densities of 1s excitons were created by cw-laser excitation while the interexcitonic 1s to 2p transitions were probed simultaneously, using Fourier spectroscopy. Our data give evidence for a surprisingly large splitting of the 2p level (3,7 meV) the origin of which is a matter of speculation. An analysis of lineshape and width of the transitions results in a ratio of the effective masses m 1s /m 2p which deviates from the literature value.