  Generation and manipulation of exciton polaritons with controllable spin
could deeply impact spintronic applications, quantum simulations, and quantum
information processing, but is inherently challenging due to the charge
neutrality of the polariton and the device complexity it requires. In this
work, we demonstrate electrical generation of spin-polarized exciton polaritons
in a monolithic dielectric perovskite metasurface embedded in a light-emitting
transistor. A finely tailored interplay of in- and out-of-plane symmetry
breaking of the metasurface allows to lift the spin degeneracy through the
polaritonic Rashba effect, yielding high spin purity with normalized Stokes
parameter of S3~0.8. Leveraging on spin-momentum locking, the unique
metatransistor device architecture enables electrical control of spin and
directionality of the polaritonic emission. This work advances the development
of compact and tunable spintronic devices, and represents an important step
toward the realization of electrically pumped inversionless spin-lasers.
