Momentum-space spin texture induced by strain gradient in nominally centrosymmetric SrIrO₃ films

Spin texture in k-space is a consequence of spin splitting due to strong spin-orbit coupling and inversion symmetry breaking. It underlies fertile spin transport phenomena and is of crucial importance for spintronics. Here, we observe the spin texture in k-space of nominally centrosymmetric SrIrO₃ grown on NdGaO₃ (110) substrates, using non-linear magnetotransport measurements. We demonstrate that the spin texture is not only induced by the interface, which inherently breaks the inversion symmetry in strong spin-orbit coupled SrIrO₃ films, but also originates from the film bulk. Structural analysis reveals that thicker SrIrO₃ films exhibit a strain gradient, which could be considered as a continuous change in the lattice constant across different layers and breaks the inversion symmetry throughout the entire SrIrO₃ films, giving rise to the spin texture in k-space. First-principles calculations reveal that the strain gradient creates large spin-splitting bands, inducing the spin texture with anisotropy, which is consistent with our experimental observations. Our results offer an efficient method for inducing the spin textures in k-space.