Even exciton series in Cu2O

Article

关键词: POLARIZATION DEPENDENCE;    CYCLOTRON-RESONANCE;    2-PHOTON ABSORPTION;    PHONON INTERACTION;    FINE-STRUCTURE;    ENERGY-BANDS;    SEMICONDUCTORS;    GERMANIUM;    SYMMETRY;    EXCHANGE;   

DOI  :  10.1103/PhysRevB.95.195201

来源: SCIE

【 摘 要 】

Recent investigations of excitonic absorption spectra in cuprous oxide (Cu2O) have shown that it is indispensable to account for the complex valence-band structure in the theory of excitons. In Cu2O, parity is a good quantum number and thus the exciton spectrum falls into two parts: the dipole-active exciton states of negative parity and odd angular momentum, which can be observed in one-photon absorption (Gamma(-4) symmetry), and the exciton states of positive parity and even angular momentum, which can be observed in two-photon absorption (Gamma(+5) symmetry). The unexpected observation of D excitons in two-photon absorption has given first evidence that the dispersion properties of the Gamma(+5) orbital valence band are giving rise to a coupling of the yellow and green exciton series. However, a first theoretical treatment by Uihlein et al. [Phys. Rev. B 23, 2731 (1981)] was based on a simplified spherical model. The observation of F excitons in one-photon absorption is a further proof of a coupling between yellow and green exciton states. Detailed investigations on the fine structure splitting of the F exciton by F. Schweiner et al. [Phys. Rev. B 93, 195203 (2016)] have proved the importance of a more realistic theoretical treatment including terms with cubic symmetry. In this paper we show that the even and odd parity exciton system can be consistently described within the same theoretical approach. However, the Hamiltonian of the even parity system needs, in comparison to the odd exciton case, modifications to account for the very small radius of the yellow and green 1S exciton. In the presented treatment, we take special care of the central-cell corrections, which comprise a reduced screening of the Coulomb potential at distances comparable to the polaron radius, the exchange interaction being responsible for the exciton splitting into ortho and para states, and the inclusion of terms in the fourth power of p in the kinetic energy being consistent with Oh symmetry. Since the yellow 1S exciton state is coupled to all other states of positive parity, we show how the central-cell corrections affect the whole even exciton series. The close resonance of the 1S green exciton with states of the yellow exciton series has a strong impact on the energies and oscillator strengths of all implied states. The consistency between theory and experiment with respect to energies and oscillator strengths for the even and odd exciton system in Cu2O is a convincing proof for the validity of the applied theory.

【 授权许可】

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