Chirped Floquet linear drives activate forbidden charge-to-spin conversions in Rashba two-dimensional electron gases

Abstract

In Rashba two-dimensional electron gases (2DEGs), charge-to-spin conversion via the Edelstein effect is conventionally limited to the transverse plane. Accessing longitudinal or out-of-plane pathways typically requires static magnetic fields or interface engineering, which cause stray fields and lack tunability. While dynamic circular or elliptical Floquet drives can also unlock these forbidden pathways, a simple Floquet linear drive cannot. Here, we propose an alternative approach: a \textit{chirped} Floquet linear drive. The chirp induces in-plane Floquet-Zeeman fields and an odd-parity momentum drift, which simultaneously break rotational and time-reversal symmetries. This mechanism activates the forbidden Edelstein charge-to-spin conversions in Rashba 2DEGs. Experimentally accessible via programmable spatial light modulators or optical delay lines, this tunable chirped linear drive offers a broadly applicable route to spin-orbit torque switching and high-efficiency spintronics.