Optically Erasing Disorder in Semiconductor Microcavities with Dynamic Nuclear Polarization

The mean squared value of the photonic disorder is found to be reduced by a factor of 100 in a typical GaAs based microcavity when exposed to a circularly polarized continuous wave optical pump without any special spatial patterning. Resonant excitation of the cavity mode excites a spatially nonuniform distribution of spin-polarized electrons, which depends on the photonic disorder profile. Electrons transfer spin to nuclei via the hyperfine contact interaction, inducing a long-living Overhauser magnetic field able to modify the potential of exciton polaritons.

Figure 1

(a) Schematic of a semiconductor microcavity formed by distributed Bragg reflectors (DBRs) and a QW. (b) Dispersion of the different modes of the system. Excitons are strongly coupled to a cavity mode forming the polariton branches. Our scheme considers an optical pump exciting free electron-hole pairs at an energy near resonant with the cavity photon branch.

Figure 2

(a) Dependence of the steady-state nuclear polarization (blue solid curve), as a fraction of complete polarization, on the detuning between the cavity photon energy and pump energy. The dashed green curve shows the excited electron density. (b) The dependence of the lower polariton energy without (blue solid curve) and with (green dashed curve) the influence of dynamically polarized nuclei on the cavity photon-pump detuning. In the range marked in gray, $E_{\mathrm{LP}}({\mathbf{x}}_{\parallel })$ is roughly constant with respect to $E_C({\mathbf{x}}_{\parallel })$. Parameters are $L=15\mathrm{nm}$, ${\nu }_0=(5.65\AA {)}^3/2$, $A=90\mu \mathrm{eV}$ [11] (this represents an average for ${}^{69}\mathrm{Ga}$, ${}^{71}\mathrm{Ga}$, and ${}^{75}\mathrm{As}$ nuclei), $Q=5$ [8, 34], $T_d=10\mathrm{ms}$, $\Gamma =0.12\mathrm{meV}$, $V=2.55\mathrm{meV}$ [32]. The (average) photon-exciton detuning was taken as 3 meV.

Figure 3

Typical variation of the lower polariton energy in space without [lower curve in (a) and lower surface in (b)] and with (upper curve and upper surface) the influence of nuclear spins. The photonic disorder was modeled with a correlation length of $2\mu \mathrm{m}$ and rms amplitude 0.04 meV.