Spin currents of exciton polaritons in microcavities with (110)-oriented quantum wells

We study the polarization optical properties of microcavities with embedded (110)-oriented quantum wells. The spin dynamics of exciton polaritons in such structures is governed by the interplay of the spin-orbit splitting of exciton states, which is odd in the in-plane momentum, and the longitudinal-transverse splitting of cavity modes, which is even in the momentum. We demonstrate the generation of polariton spin currents by a linearly polarized optical pump and analyze the arising polariton spin textures in the cavity plane. By tuning of the excitation spot size, which controls the polariton distribution in the momentum space, one obtains symmetric or asymmetric spin textures.

Figure 1

Pure spin current of excitons in a (110)-oriented QW. Optical pumping at the normal incidence of light upon the QW generates excitons at $\mathit{k}=0$. Due to $k_x$-linear terms in the energy spectrum, excitons with the spin projections $\pm 1$ posses nonzero group velocities $v_x$ at $\mathit{k}=0$ and move in the opposite directions.

Figure 2

Spatial distribution of the Stokes parameters determining the polarization of polaritons for linearly polarized pump and the pump-spot radius $r_0=20$ $\mu \mathrm{m}$. (a)–(c) and (d)–(f) Calculated for the spin-orbit coupling parameters ${\gamma }_X=50$ meV Å and ${\gamma }_X=100$ meV Å, respectively. The central area has a strong linear polarization stemming from the pump polarization, overshadowing the polarization conversion in (a), (c), (d), and (f).

Figure 3

Spatial distribution of the Stoke parameter ${\rho }_{\text{circ}}$ determining the circular polarization of polaritons for different pump-spot radii. The pump is linearly polarized along the $x$ axis, ${\gamma }_X=100$ meV Å. The central area has a strong linear polarization stemming from the pump polarization, overshadowing the polarization conversion.

Figure 4

Spatial distribution of the Stokes parameters determining the polarization of polaritons for linearly polarized pump and the pump-spot radius $r_0=2$ $\mu \mathrm{m}$. (a)–(c) and (d)–(f) Calculated for the spin-orbit coupling parameters ${\gamma }_X=0$ meV Å and ${\gamma }_X=100$ meV Å, respectively.