Artificial oxide heterostructures with non-trivial topology

Abstract

In the quest for topological insulators with large band gaps, heterostructures with Rashba spin–orbit interactions come into play. Transition metal oxides with heavy ions are especially interesting in this respect. We discuss the design principles for stacking oxide Rashba layers. Assuming a single layer with a two-dimensional electron gas (2DEG) on both interfaces as a building block, a two-dimensional topological insulating phase is present when negative coupling between the 2DEGs exists. When stacking multiple building blocks, a two-dimensional or three-dimensional topological insulator is artificially created, depending on the intra- and interlayer coupling strengths and the number of building blocks. We show that the three-dimensional topological insulator is protected by reflection symmetry, and can therefore be classified as a topological crystalline insulator. In order to isolate the topological states from bulk states, the intralayer coupling term needs to be quadratic in momentum. It is described how such a quadratic coupling could potentially be realized by taking buckling within the layers into account. The buckling, thereby, brings the idea of stacked Rashba system very close to the alternative approach of realizing the buckled honeycomb lattice in [111]-oriented perovskite oxides.

Large Nonlinear Transverse Conductivity and Berry Curvature in KTaO3 Based Two-Dimensional Electron Gas

“…The mechanisms for generating Berry curvature include SOC, orbit hybridization, etc. 32 It is thus highly desirable to study the Berry curvature related transverse nonlinear transport in KTO based 2DEG, which exhibits a large SOC and multiple d-orbit hybridizations.…”

“…Although oxide heterostructures represent a large family of materials with inversion symmetry breaking, a demonstration of transverse nonlinear transport is still lacking in these materials. The mechanisms for generating Berry curvature include SOC, orbit hybridization, etc . It is thus highly desirable to study the Berry curvature related transverse nonlinear transport in KTO based 2DEG, which exhibits a large SOC and multiple d-orbit hybridizations.…”

Oxide materials as building blocks for artificial topological insulators

“…For simplicity we assume that the strength of the coupling for the nearest neighbour and second nearest neighbour is the same. Taken with permission from [319].…”

“…This section is published as part of: P. M. Gunnik, R. L. Bouwmeester and A. Brinkman, Artificial oxide heterostructures with non-trivial topology, Journal of Condensed Matter Physics 33, 085601 (2020)[319].…”