THz-Driven Floquet Spin Valve-Modulator

Abstract

Within the scattering matrix ($S$-matrix) framework adapted to the high-frequency Floquet--Magnus formalism based on the length gauge, we investigate spin-dependent quantum transport in a 1D quantum ring with an asymmetric ($\pi /2$) configuration of quantum point contacts. We demonstrate the realization of a contactless electromagnetic analog of the Datta--Das spin field-effect transistor with ferromagnetic leads operating at zero static magnetic field. It is shown that an off-resonance terahertz (THz) field enables high-precision switching between spin channels without altering the static parameters of the nanostructure. Driven by an electronic Vernier effect, the quantum interference in the asymmetric geometry yields a selective spin phase rotator alongside an ultra-high-contrast current-suppression regime (``optical shutter''). The proposed architecture is fundamentally robust against multiphoton leakage sidebands, offering a thermally immune, high-speed alternative to conventional semiconductor static spin transistors.

arXiv comment73 pages, 5 figures. In the revised version, a number of typos have been corrected. Estimates for various quantities have been added, which support the model's suitability for practical implementation. References 7, 8, 9, 38, 39, and 40 have been added