# Robust semi-Dirac points and unconventional topological phase transitions in doped superconducting Sr2IrO4 tunnel coupled to t2g electron systems

## TL;DR

This paper demonstrates that robust semi-Dirac points can naturally occur in heterostructures of Sr2IrO4 and t2g electron systems without fine-tuning, revealing new topological phase transitions and stable Dirac points.

## Contribution

It introduces a model where semi-Dirac points are topologically stable in heterostructures without fine-tuning, and explores their splitting into Dirac points in multilayer configurations.

## Key findings

- Semi-Dirac points are stable without fine-tuning in Sr2IrO4 and t2g-ES heterostructures.
- Coupling to multiple layers causes semi-Dirac points to split into Dirac points with opposite chiralities.
- Predicted rich topological phase diagram for Sr2RuO4 as a t2g-ES example.

## Abstract

Semi-Dirac fermions are known to exist at the critical points of topological phase transitions requiring fine-tuning of the parameters. We show that robust semi-Dirac points can appear in a heterostructure consisting of superconducting Sr2IrO4 and a t2g electron system (t2g-ES) without fine-tuning. They are topologically stable in the presence of the symmetries of the model, metallic t2g-ES and a single active band in Sr2IrO4. If the t2g metal is coupled to two different layers of Sr2IrO4 (effectively a multiband superconductor) in a three-layer-structure the semi-Dirac points can split into two stable Dirac points with opposite chiralities. A similar transition can be achieved if the t2g-ES supports intrinsic triplet superconductivity. By considering Sr2RuO4 as an example of a t2g-ES we predict a rich topological phase diagram as a function of various parameters.