Confinement-driven electronic and topological phases in corundum-derived 3d-oxide honeycomb lattices

摘要

Using density functional theory calculations including an on-site Coulomb term, we explore electronic and possibly topologically nontrivial phases in 3d transition-metal oxide honeycomb layers confined in the corundum structure (alpha-Al2O3) along the [0001] direction. In most cases the ground state is a trivial antiferromagnetic Mott insulator, often with distinct orbital or spin states compared to the bulk phases. With imposed symmetry of the two sublattices the ferromagnetic phases of (X2O3)(1)/(Al2O3)(5)(0001) with X = Ti, Mn, Co, and Ni exhibit a characteristic set of four bands, two that are relatively flat and two with a Dirac crossing at K, associated with the single-electron occupation of e'(g) (Ti) or e(g) (Mn, Co, Ni) orbitals. Our results indicate that the Dirac point can be tuned to the Fermi level using strain. Applying spin-orbit coupling (SOC) leads to a substantial anomalous Hall conductivity with values up to 0.94 e(2)/h. Moreover, at aAl(2)O(3) = 4.81 angstrom we identify a particularly strong effect ;of SOC with an out-of-plane easy axis for (Ti2O3)(1)/(Al2O3)(5)(0001) which stabilizes the system dynamically. Due to the unusually high orbital moment of -0.88 mu B that nearly compensates the spin moment of 1.01 mu B, this system emerges as a candidate for the realization of the topological Haldane model of spinless fermions. Parallels to the perovskite analogs (LaXO3)(2)/(LaAlO3)(4)(111) are discussed.