Topological Phases in Perovskite Iridates with Strong Spin-Orbit Coupling

The study of topological phases of matter has attracted much attention recently, providing a promising route to understanding the classification of various phases in condensed matter physics. The Iridates, which are Iridium-based compounds, have already shown rich physical phenomena and can be a perfect platform to reveal topological phases in materials with strong spin-orbit coupling. This thesis focuses on possible exotic topological phases that stem from the interplay between strong spin-orbit coupling and non-trivial band structure in three-dimensional perovskite Iridates and other layered Iridate materials. Firstly, motivated from previous band structure results of SrIrO 3, we predict that three-dimensional perovskite Iridates can realize a new class of metals dubbed “topological crystalline metals” with surface states protected by lattice symmetry and a pair of topological invariants. We show that these novel metallic phases can give rise to various non-trivial topological phases when different symmetries are broken, including a Weyl and nodal-line semimetal. Secondly, we provide a generic condition to identify a novel three-dimensional topological semi-metallic phase in materials with strong spin-orbit coupling. Such a semi-metallic phase is featured by bulk gapless four-fold degenerate nodal-line excitations. By using perovskite Iridates SrIrO3 as an example, we give an explicit mathematical proof on the validity of this condition as well as verify the existence of such bulk nodal-line band degeneracy in the tight-binding model. Thirdly, we propose that a topological insulator can exist in a two-dimensional single layer Iridium oxide superlattice under certain lattice distortions; a tight-binding model is constructed using the basis of an effective J eff=1/2 pseudo-spins. A topological magnetic insulator with quantum anomalous Hall effect is found in the bilayer superlattice when a magnetic order or magnetic field is present in the system. Lastly, a pair of helical Majorana fermions emerges at the interface of a two-dimensional Weyl semimetal and a d-wave superconductor. We focused on the most promising and feasible realization: Iridium oxide layer without inversion symmetry, which is classified as Weyl semimetal, in proximity to d-wave high temperature Cuprates. In conclusion, we provide some future directions related to the topological phases in Iridates.

Department dc:contributor.department

Physics

Year dc:date.issued

2017

Author dc:creator

• CHEN, YIGE

Advisor dc:contributor.advisor

• Kee, Hae-Young

Handle dc:identifier.uri

http://hdl.handle.net/1807/80986

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/80986