  The recent discovery of materials hosting persistent spin texture (PST) opens
an avenue for the realization of energy-saving spintronics since they support
an extraordinarily long spin lifetime. However, the stability of the PST is
sensitively affected by symmetry breaking of the crystal induced by external
perturbation such as the electric field. In this paper, through
first-principles calculations supplemented by symmetry analysis, we report the
emergence of the robust and stable PST with large spin splitting in the
two-dimensional ferroelectric bilayer WTe$_{2}$. Due to the low symmetry of the
crystal ($C_{s}$ point group), we observe a canted PST in the spin-split bands
around the Fermi level displaying a unidirectional spin configuration tilted
along the $yz$ plane in the first Brillouin zone. Such a typical PST can be
effectively reversed by out-of-plane ferroelectric switching induced by
interlayer sliding along the in-plane direction. We further demonstrated that
the reversible PST is realized by the application of an out-of-plane external
electric field. Thus, our findings uncover the possibility of an electrically
tunable PST in the 2D materials, offering a promising platform for highly
efficient spintronics devices.
