Polarization Bistability and Resultant Spin Rings in Semiconductor Microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Figure 1

(a)–(d) Normal incidence transmitted intensity versus external pump power for ${\rho }_P=1$, 0.6, 0.4, and 0. Triangles (blue circles) correspond to the intensity of the ${\sigma }^{+}$ (${\sigma }^{-}$) component. Arrows show the direction in which the pump intensity is varied. (e)–(h) Corresponding DCP of transmission versus pump power. Gray dotted lines serve as a guide to the eye. The inset in (e) shows a schematic of the experimental geometry for (a)–(h). (k) Schematic diagram of OPO. (l) and (m) Polar plots of normalized signal (dashed line) and the laser intensity (continuous line) for TE (l) and TM (m) polarized pump.

Figure 2

The calculated dependences of the MC transmission intensity vs pump intensity, for several DCP of the pump beam ($\rho$). The ${\sigma }^{+}$ (${\sigma }^{-}$) component is shown by triangles (blue lines). ▹ (◃) correspond to increasing (decreasing) pump power. The Rabi splitting, detuning between exciton and photon mode, and detuning between laser energy and LP branch are the same as in the experiment.

Figure 3

Real space images of intensity (a)–(d) and corresponding DCP (e)–(h) of the transmitted beam for elliptically (${\rho }_P=0.6$) polarized pump beam at different pump powers. The images (contour lines) in (a)–(d) show the intensity of the ${\sigma }^{+}$ (${\sigma }^{-}$) component.