Optically induced orbital polarization in bulk germanium

Abstract

Optical orientation has been proven as a powerful tool to inject spin-polarized electron and hole populations in III-V and group-IV semiconductors. In particular, the absorption of circularly-polarized light in bulk Ge generates a spin-oriented population of electrons in the conduction band with a spin-polarization up to 50%, whereas the hole spin-polarization, opposite to the electron one, can even reach values up to 83%. In this letter, we theoretically investigate the optical injection of orbital polarization by means of circularly-polarized light in bulk Ge and we show that the latter considerably exceeds 100% for holes and photon energies close to the direct Ge gap. These results suggest that Ge is a convenient platform for future development of orbitronics and opto-orbitronic devices.

Figures (5)

• Figure 1: Bandstructure of bulk germanium.
• Figure 2: (a) Total carrier injection tensor $\xi^{xx}(\omega)$ as a function of the incident photon energy. (b) Decomposition of the total carrier injection rate from HH, LH and SO bands.
• Figure 3: (a) Electron spin injection pseudotensor $\zeta^{xyz}_\mathrm{e}(\omega)$ as a function of the incident photon energy. (b) Decomposition of $\zeta^{xyz}_\mathrm{e}(\omega)$ from HH, LH and SO bands. (c) Electron orbital injection pseudotensor $\eta^{xyz}_\mathrm{e}(\omega)$ as a function of the incident photon energy. (b) Decomposition of $\eta^{xyz}_\mathrm{e}(\omega)$ from HH, LH and SO bands.
• Figure 4: (a) Hole spin injection pseudotensor $\zeta^{xyz}_\mathrm{h}(\omega)$ as a function of the incident photon energy. (b) Decomposition of $\zeta^{xyz}_\mathrm{h}(\omega)$ from HH, LH and SO bands. (c) Hole orbital injection pseudotensor $\eta^{xyz}_\mathrm{h}(\omega)$ as a function of the incident photon energy. (b) Decomposition of $\eta^{xyz}_\mathrm{h}(\omega)$ from HH, LH and SO bands.
• Figure 5: Photon energy dependence of the degree of (a) electron spin polarization DSP$_\mathrm{e}$ (b) hole spin polarization DSP$_\mathrm{h}$ (c) electron orbital polarization DOP$_\mathrm{e}$ (d) hole orbital polarization DOP$_\mathrm{h}$.