Robust semi-Dirac points and unconventional topological phase transitions in superconductor/metal heterostructures

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 two-dimensional superconductor/metal heterostructures without fine-tuning if one of the layers supports a large intraionic spin-orbit coupling [1]. These semi-Dirac points are topologically stable in the presence of time-reversal and two-fold rotational symmetries, and a single active band in the superconductor. If the metallic layer is tunnel coupled to two different superconductors (effectively a multiband superconductor) in a three-layer-structure the semi-Dirac points can split into two stable Dirac points with opposite chiralities. As an example we consider a heterostructure consisting of layers of superconducting Sr₂IrO₄ and a metallic t_2g electron system, and we predict a rich topological phase diagram as a function of various parameters.

[1] M. Horsdal and T. Hyart, arXiv:1705.02987.