Fine structure of excitonic excited states in diamond studied by broadband terahertz time-domain spectroscopy

Diamond provides a unique excitonic fine structure not seen in conventional semiconductors. Here, we have applied deep-ultraviolet pump and broadband terahertz probe spectroscopy to investigate internal transitions of excitons in intrinsic diamond. Transient absorption spectra clearly show a fine structure splitting in the 2P state of the exciton, that comes from the spin-orbit interaction and the mass anisotropy of electrons and holes. Splitting energies and relative oscillator strengths are reproduced well by the theoretical model.