Tuneable Nonlinear Spin Response in a Nonmagnetic Semiconductor

Nonlinear effects and dynamics are found in a wide range of research fields. In magnetic materials, nonlinear spin dynamics enables ultrafast manipulation of spin, which promises high-speed nonvolatile information processing and storage for future spintronic applications. However, a nonlinear spin response is not yet demonstrated in a nonmagnetic material that lacks strong magnetic interactions. Dilute nitride III-V materials, e.g., (Ga,N)As, have the ability to amplify the conduction-electron-spin polarization by filtering out minority spins via spin-polarized defect states at room temperature. Here, by employing coupled rate equations, we theoretically demonstrate the emergence of a nonlinear spin response in such a defect-enabled room-temperature spin amplifier. Furthermore, we showcase the proposed spin nonlinearity in a (Ga,N)As-InAs quantum dot (QD) coupled all-semiconductor nanostructure, by measuring the higher-harmonic generation, which converts the modulation of excitation polarization into the second-, third-, and fourth-order harmonic oscillations of the QD's photoluminescence intensity and polarization. The observed spin nonlinearity originates from defect-mediated spin-dependent recombination, which can be conveniently tuned with an external magnetic field and can potentially operate at a speed exceeding 1 GHz. The demonstrated spin nonlinearity could pave the way for nonlinear spintronic and optospintronic device applications based on nonmagnetic semiconductors with simultaneously achievable high operation speed and nonlinear response.