From trigonal to triclinic: Symmetry-tuned Rashba effects in buckled honeycomb SrHfO${}_3$-based heterostructures

Harnessing the interplay of symmetry breaking and spin-orbit coupling, we investigate Rashba spin splitting in buckled honeycomb (SrHfO${}_3$)${}_2$/(LaAlO${}_3$)${}_4$(111) superlattices using density functional theory (DFT) calculations with a Hubbard $U$ term and a Wannier-based tight-binding (TB) model. In the non-centrosymmetric $P1$ phase, pronounced Rashba-type splitting emerges near the $M$ and $K$ points accompanied by a helical in-plane spin texture, while the centrosymmetric $P321$ phase remains spin-degenerate. A Wannier-based tight-binding Hamiltonian, extended analytically with on-site spin-orbit coupling, reproduces the DFT results. A Rashba coefficient of ${\alpha }_R=0.34$ eV$\cdot$ Angstrom and energy $E_R=29$ meV are extracted directly from the DFT band structure placing the system among moderately strong oxide Rashba materials. $\mathrm{\Gamma }$-phonon calculation confirms the dynamical stability of the $P1$ structure and the results reveal the critical role of symmetry breaking and inter-orbital hybridization in enabling Rashba effects, supported by enhanced imaginary second-nearest-neighbor hoppings and Berry curvature. These findings establish SrHfO${}_3$-based buckled heterostructures as a promising platform for engineering Rashba effects in oxide-based spintronic devices.