Rashba spin splitting and anomalous spin textures in the bulk ferroelectric oxide perovskite KIO3

Abstract

The momentum-dependent Rashba and Dresselhaus spin splitting has gained much attention for its highly promising applications in spintronics. A non-centrosymmetric structure and the presence of spin–orbit coupling (SOC) lead to the momentum-dependent spin splitting of degenerate bands at non-time-reversal-invariant k-points. This lifts the Kramers degeneracy leading to Rashba and Dresselhaus splitting. In the search for new ferroelectric Rashba semiconductors, here we present ferroelectric oxide perovskite KIO₃, where the presence of a heavy element (I), contributing to significant SOC and inversion asymmetric nature induces interesting band splitting. By employing the state-of-the-art density functional theory (DFT) with the semi-local and hybrid functional (HSE06) combined with SOC, we find non-negligible spin splitting effects at the 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 the k·p model Hamiltonian. Linear Rashba terms successfully explain splitting at the VBM. However, cubic terms become important in realizing spin-orientation near the CBm. In the R3c phase, the four-band k·p model Hamiltonian is needed to completely understand the anomalous nature of the spin textures, which is beyond the conventional linear Rashba and Dresselhaus splitting. Our results show the enhancement in Rashba parameters on tuning the epitaxial strain. Furthermore, we have observed a reversal of spin-orientation upon switching the direction of polarization.