Rashba Spin-Splitting and Anomalous Spin Textures in the Bulk Ferroelectric Oxide Perovskite KIO₃

The momentum-dependent Rashba and Dresselhaus spin-splitting has gained much attention for its highly promising applications in spintronics. Non-centrosymmetric structure and presence of spin-orbit coupling (SOC), lead to momentum-dependent spin-splitting of degenerate bands at non-time-reversal-invariant k-points. This lifts the Kramer’s degeneracy leading to Rashba and Dresselhaus splitting. In search of new ferroelectric Rashba semiconductors, here we present ferroelectric oxide perovskite KIO₃, where the presence of heavy element (I), significant SOC and inversion asymmetric nature induce interesting band splitting. By employing state-of-the-art density functional theory (DFT) with semi-local and hybrid functional (HSE06) combined with SOC, we find non-negligible spin-splitting effect at conduction band minimum (CBm) and valence band maximum (VBM) for R3m and R3c phases. For a deeper understanding of the observed spin-splitting, we have analyzed the spin textures within the combined framework of DFT and k.p model Hamiltonian. Linear Rashba terms successfully explain the splitting at VBM. However, cubic terms become important in realizing spin-orientation near CBm. In R3c phase, four-band k.p model Hamiltonian including the pure orbital-degree of freedom coupled with the spin-degree of freedom is needed to completely understand the anomalous nature of the spin textures, which is beyond the conventional linear Rashba and Dresselhaus splitting. In a nonmagnetic system without SOC, all symmetry-protected degenerate levels are referred to as PODF. Our results show the enhancement in Rashba parameters on tuning the epitaxial strain. Further, we have observed reversal of spin-orientation on switching the direction of polarization.