Doping-induced persistent spin helix with a large spin splitting in monolayer SnSe

Finding a new class of materials supporting a long spin lifetime is essential in development of energy-saving spintronics, which is achievable by using persistent spin helix (PSH) materials. However, for spintronic devices, the PSH states with large spin splitting are required for operation at room temperature. By employing first principles calculations, we show that the PSH states with large spin splitting are achieved in the SnSe monolayer functionalized by a substitutional halogen impurity. We find the PSH states in the Fermi level where k-space Fermi surface is characterized by the shifted two loops, dominated by out-of-plane spin orientations. We clarify the PSH states in terms of an effective (k) over right arrow . (p) over right arrow Hamiltonian obtained from symmetry consideration. Finally, large spin-orbit strength in the PSH states with a substantially small wavelength is found, rendering that this system is promising for the development of efficient and high-density scalable spintronic devices operating at room temperatures.