Searching for two-dimensional Weyl superconductors in heterostructures

TL;DR

This paper proposes a method to realize two-dimensional Weyl superconductors in heterostructures of half-metal and spin-singlet superconductor, revealing novel topological phases, Lifshitz transitions, and the first example of a type-II Weyl node with superconductivity.

Contribution

It introduces a new heterostructure design for 2D Weyl superconductors, demonstrating their robustness and novel topological features, including type-II Weyl nodes with superconducting correlations.

Findings

Robust 2D Weyl superconductor realized in d-wave heterostructures.

Observation of Lifshitz transitions with magnetization orientation.

First example of a type-II Weyl node in a superconducting system.

Abstract

Two-dimensional Weyl superconductor is the most elusive member of a group of materials with Weyl fermions as low-energy excitations. Here, we propose to realize this state in a heterostructure consisting of thin films of half-metal and spin-singlet superconductor. In particular, for the $d$-wave case, a very robust two-dimensional Weyl superconductor (dWSC) is realized independent of the orientation of the spontaneous magnetization of the half-metal. The quasiparticle spectra of the dWSC show interesting evolution with the direction of the magnetization, featured by a series of Lifshitz transitions in the zero-energy contour of the quasiparticle spectrum. For a general magnetization orientation of the half-metal, the state is a combination of a superconducting component and a normal fluid component and is different from all known forms of pairings. In addition, we find a transition between type-I and type-II Weyl nodes. This is also the first example of a type-II Weyl node in the presence of superconducting correlation. The symmetries and topological properties of the system are analyzed. We also study the phases in the heterostructure with the half-metal replaced by a ferromagnetic metal with a partially spin-polarized Fermi surface.