Field-Tunable Spin–Valley Polarized Transport in Zigzag Germanene Nanoribbons

Valleytronics has emerged as a rapidly developing field in recent years. However, transmitting information via valley currents faces significant challenges. In most candidate materials, the lack of intrinsic symmetry protection facilitates intervalley scattering. This mixing of valley currents from the K and K ' valleys disrupts the directional integrity of carrier flow. Indeed, spin-valley polarization can reduce intervalley scattering probability, thereby improving the accuracy and stability of valley-current transport. In this work, we use a local electric field in zigzag germanene nanoribbons (ZGeNR) exhibiting the quantum Hall (QH) effect to achieve the quantum spin-valley Hall (QSVH) effect, generating two counter-propagating spin-valley polarized currents. Subsequently, applying a global electric field separates these two oppositely polarized currents in energy, yielding a singly spin-valley polarized current. This system can be employed to design programmable polarized current sources and shows promise for realizing singly spin-valley polarized Andreev reflection.