Electrical Spin Injection and Helicity Modulation in a Room Temperature Polariton Laser

Room temperature elliptically polarized inversionless coherent emission, or polariton lasing, is observed from a bulk GaN-based edge-emitting microcavity diode operated with spin-polarized electrical injection. The low nonlinear threshold for polariton lasing occurs at 69 A/cm$^{\mathrm{2}}$ in the light-current characteristics, accompanied by a collapse of the emission linewidth to 1 meV and a blueshift of 1.87 meV of the emission peak. Sub-threshold angle-resolved measurements confirm strong-coupling regime of operation of the microcavity diodes (cavity Q $=$ 3200) with a cavity-to-exciton detuning of -- 11.6 meV and a vacuum-field Rabi splitting of 36.4 meV. Laser operation with a spin-polarized current, after in-plane magnetization, results in a maximum degree of output circular and linear polarization of 47 {\%} and 33 {\%} respectively, above the condensation threshold, at a field of $+$ 1.6 kOe. The magnitude and helicity of the output circular polarization is deterministically governed by the in-plane H field. The results have been analyzed using the Gross-Pitaevskii equations for the spinor exciton-polariton condensate and the calculated results agree with the measured data.