Intrinsic persistent spin texture in two-dimensional T−XY ( X, Y=P , As, Sb, Bi;

Persistent spin texture (PST) can maintain a uniform spin configuration in the momentum space, resulting in a spatially periodic mode known as a persistent spin helix (PSH). The PSH is robust against spin-independent scattering and renders an extremely long spin lifetime, which can improve the performance of potential spintronic devices. Here, $T\text{\ensuremath{-}}XY$ ($X\ensuremath{\ne}Y=\mathrm{P}$, As, Sb, and Bi) monolayers with dynamical, mechanical, and thermal stabilities are predicted to intrinsically possess PST. Due to the ${C}_{2\ensuremath{\upsilon}}$ point-group symmetry, a unidirectional spin configuration is preserved in the out-of-plane direction for both conduction and valence bands around the high-symmetry $\mathrm{\ensuremath{\Gamma}}$ point. That is, the expectation value of the spin $S$ only has the out-of-plane component ${S}_{z}$. The application of an out-of-plane external electric field can induce in-plane components ${S}_{x}$ and ${S}_{y}$, thus offering a promising platform for the on-off logical functionality of spin devices. Our work reveals an alternative family of $T$-phase two-dimensional (2D) materials, which could provide promising applications in spintronic devices.