Giant spin splitting and its origin in methylhydrazinium lead halide perovskites

Spin splitting, or removal of spin degeneracy in the electronic energy band/level, is often a measure of spin-orbit coupling strength and a way to manipulate spin degrees of freedom. We use first-principles simulations to predict giant spin splitting in methylhydrazinium lead halide (${\mathrm{MHyPbX}}_3, \mathrm{MHy}={\mathrm{CH}}_3{\mathrm{NH}}_2{\mathrm{NH}}_2, X$ = Br and Cl) hybrid organic-inorganic perovskites. The values can reach up to 408.0 meV at zero Kelvin and 281.6 meV at room temperature. The origin of the effect is traced to the large distortion of ${\mathrm{PbX}}_3$ framework, driven primarily by Pb ions in the ferroelectric ${\mathrm{\Gamma }}^{3-}$ mode. The Pb displacements consist of a combination of polar and antipolar arrangements and result in up to 39.2 meV/atom enhancement of the spin-orbit coupling energy in the polar phase of the materials. The spin-orbit coupling gives origin to persistent spin textures in ${\mathrm{MHyPbX}}_3$, which are desirable for applications in spintronics and quantum computing. Our findings reveal an additional functionality for hybrid organic-inorganic perovskite and open a way for the design of more materials with giant spin splitting.