Duality in topological superconductors and topological ferromagnetic insulators in a honeycomb lattice

TL;DR

This paper reveals a duality between topological superconductors and ferromagnetic insulators in a honeycomb lattice, showing how topological phases can be controlled via chemical potential and exploring phase transitions and Majorana modes.

Contribution

It introduces a dual transformation linking a $d+id$ superconductor to ferromagnetic insulators, enabling control over topological phases and revealing new superconducting states.

Findings

Topological phase transition from chiral to quasi-helical superconductor.

Control of topological properties via chemical potential tuning.

Access to high Chern number phases with Majorana modes.

Abstract

The ground state of large Hubbard $U$ limit of a honeycomb lattice near half-filling is known to be a singlet $d+id$-wave superconductor. It is also known that this $d+id$ superconductor exhibits a chiral $p+ip$ pairing locally at the Dirac cone, characterized by a $2\mathbb{Z}$ topological invariant. By constructing a dual transformation, we demonstrate that this $2\mathbb{Z}$ topological superconductor is equivalent to a collection of two topological ferromagnetic insulators. As a result of the duality, the topology of the electronic structures for a $d+id$ superconductor is controllable via the change of the chemical potential by tuning the gate voltage. In particular, instead of being always a chiral superconductor, we find that the $d+id$ superconductor undergoes a topological phase transition from a chiral superconductor to a quasi-helical superconductor as the gap amplitude or the chemical potential decreases. The quasi-helical superconducting phase is found to be characterized by a topological invariant in the pseudo-spin charge sector with vanishing both the Chern number and the spin Chern number. We further elucidate the topological phase transition by analyzing the relationship between the topological invariant and the rotation symmetry. Due to the angular momentum carried by the gap function and spin-orbit interactions, we show that by placing $d+id$ superconductors in proximity to ferromagnets, varieties of chiral superconducting phases characterized by higher Chern numbers can be accessed, providing a new platform for hosting large numbers of Majorana modes at edges.