Interaction-driven spin-orbit effects and Chern insulating phases in corundum-based 4d and 5d oxide honeycomb lattices

Abstract

Using density functional theory calculations with a Hubbard U , we explore topologically nontrivial phases in X 2 O 3 honeycomb layers with X = 4d and 5d cation inserted in the band insulator α-Al 2 O 3 along the [0001]direction. Several promising candidates for quantum anomalous Hall insulators (QAHI) are identified. In particular, for X = Tc and Pt spin-orbit coupling (SOC) opens a gap of 54 and 59 meV, respectively, leading to Chern insulators (CI) with C = -2 and -1. The nature of different Chern numbers is related to the corresponding spin textures. The Chern insulating phase is sensitive to the Coulomb repulsion strength: X = Tc undergoes a transition from a CI to a trivial metallic state beyond a critical strength of U c = 2.5 eV. A comparison between the isoelectronic metastable FM phases of X = Pd and Pt emphasizes the intricate balance between electronic correlations and SOC: while the former is a trivial insulator, the latter is a Chern insulator. In addition, X = Os turns out to be a FM Mott insulator with an unpaired electron in the t 2g manifold where SOC induces an unusually high orbital moment of 0.34 µ B along the z-axis. Parallels to the 3d honeycomb corundum cases are discussed.

Chern and Z2 topological insulating phases in perovskite-derived 4d and 5d oxide buckled honeycomb lattices

“…3e and f. The results demonstrate that with tensile strain the CI phase is further stabilized. A similar effect of strain was observed in (Tc 2 O 3 ) 1 /(Al 2 O 3 ) 5 (0001) [29]. We note that the sign of the Chern number C = 2 for X = Tc in the (111)-oriented perovskite bilayer is reversed compared to the corundum-derived SL (C = -2) [29].…”

“…This is in agreement with the fact that only bands of minority character appear around E F . Overall, even though the number of edge states of the perovskite and corundum case (Tc [29] are identical, the differences can be attributed to the distinct studied above, we investigate the non-magnetic phases of the two d 3 systems containing the homologous elements X = Mo and W at a LAO . Despite the AFM ground state (cf .…”

“…Our previous studies [24,[27][28][29] on systems hosting the honeycomb lattice with X = 4d and 5d showed that the metastable ferromagnetic state of X = Tc, Pt host quantum anomalous Hall states. Using the insight gained from this investigation, we explore the perovskite-derived SLs with the above-mentioned TM ions.…”

“…The static local correlation effects were accounted for in the GGA +U approach, using U eff = U − J of Dudarev et al [33]. Hubbard U values for the 4d and 5d ions are typically lower than for the 3d cations [27,29]. We used an U = 3 eV for X = Tc, Pd, Mo and 1-2 eV for X = Pt, W with a Hund's exchange parameter of J = 0.5 eV on all cations.…”

“…The complex electronic behavior of corundum-derived honeycomb layers (X 2 O 3 ) 1 /(Al 2 O 3 ) 5 (0001) were recently addressed in a systematic study of the 3d series [28]. Moreover, in the 4d and 5d systems the ferromagnetic cases of X = Tc, Pt were identified as Chern insulators with C = -2 and -1 and band gaps of 54 and 59 meV, respectively [29]. This motivated us to explore here the perovskite analogues X = Tc, Pd, and Pt in (111)-oriented (LaXO 3 ) 2 /(LaAlO 3 ) 4 .…”