  The control and generation of spin-polarized currents (SPCs) without magnetic
materials and external magnetic field is a big challenge in spintronics and
normally requires spin-flip mechanism. In this work, we propose a novel method
to control and generate SPCs in stanene nanoribbons in the quantum spin Hall
(QSH) insulator regime by all electrical means without spin-flip mechanism.
This is achieved with intrinsic spin-orbit coupling in stanene nanoribbons by
tuning the relative phase of spin up and down electrons using a gate voltage,
which creates a time delay between them thereby producing alternative SPCs
driven by ac voltage. The control and generation of SPCs are demonstrated
numerically for ac transport in both transient and ac regime. Our results are
robust against edge imperfections and generally valid for other QSH insulators
such as silicene and germanene, etc. These findings establish a novel route for
generating SPCs by purely electrical means and open the door for new
applications of semiconductor spintronics.
