Magnetism and unconventional topology in LaCoO₃/SrIrO₃ heterostructure

Employing first-principles calculations, we provide microscopic insights on the curious magnetic and topological properties of LaCoO₃/SrIrO₃ heterostructure, which has been recently synthesized [Kumar Jaiswal et al., Adv. Mater. 34, 2109163 (2022)]. Our computational study unravels transfer of polar charge from SrIrO₃ to LaCoO₃, thereby reducing the Co valence from 3+ toward 2+, supporting the experimental findings. Our study further reveals the stabilization of the intermediate spin state of Co and strong ferromagnetic Co–Co coupling in the LaCoO₃ block of the heterostructure. This, in turn, is found to induce ferromagnetism in the pseudo-tetragonally structured SrIrO₃ in the heterostructure geometry, providing an understanding of the origin of magnetism, which is counter-intuitive as both LaCoO₃ and SrIrO₃ are nonmagnetic in bulk form. Most interestingly, the band structure of ferromagnetic, tetragonal structured SrIrO₃ is found to exhibit unconventional topology, manifested as C = 2 double Weyl points, which leads to the observed anomalous Hall effect. Our finding of C  =  2 double Weyl points, belonging to the class of charge-2 Dirac points, opens up the possibility of material realization of unconventional topological properties beyond the conventional Dirac and C  =  1 Weyl points, which calls for future experiments.