Rashba effects in lead-free ferroelectric semiconductor [CH3PH3]SnBr3

Abstract

First-principles density functional theory computations are used to predict Rashba effects cofunctional with ferroelectricity in a recently synthesized lead-free hybrid organic-inorganic perovskite ${\mathrm{MPSnBr}}_{3}$ (MP=methylphosphonium, ${[{\mathrm{CH}}_{3}{\mathrm{PH}}_{3}]}^{+}$). The ground state of the material is polar monoclinic with calculated spontaneous polarization of $3.01\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{cm}}^{2}$. It exhibits near band edges' spin splitting of up to 3.3 meV and Rashba coefficient up to 0.62 eV \AA{}. The spin textures have different topology in the conduction and valence band, which originates from the difference in the spin-momentum coupling strengths. They occur in two orthogonal planes of the Brillouin zone and are coupled to the direction of spontaneous polarization. These features persist at a finite temperature of 293 K. At 333 K, that is, above monoclinic to orthorhombic phase transition, spontaneous polarization is reduced to $0.15\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{C}/{\mathrm{cm}}^{2}$, while the maximum spin splitting and Rashba coefficient reduce slightly to the values of 2.9 meV and 0.41 eV \AA{}, respectively. The spin textures remain coupled with the polarization direction. We investigate the dependence of the aforementioned properties on the choice of computational methodology to extend the first-principles predictions to include finite temperature effects. We find that the predictions are sensitive to the methodology. Our study reveals the potential of ${\mathrm{MPSnBr}}_{3}$ for low-temperature applications in spintronics and quantum computing.