Nodal Topological Superconductivity Driven by Crystalline Antiunitary Symmetry in Altermagnets

TL;DR

This paper reveals a symmetry-based mechanism for nodal topological superconductivity in altermagnets, leading to robust Majorana modes and distinct nodal phases, with potential experimental signatures.

Contribution

It identifies how crystalline antiunitary symmetry constrains pairing, resulting in novel nodal topological phases in altermagnets, expanding understanding of intrinsic topological superconductivity.

Findings

Nodal phases with Majorana flat bands and chiral Majorana edge states.

Symmetry-constrained pairing persists even after symmetry breaking.

Proposed tunneling signatures to detect nodal phases and symmetry breaking.

Abstract

Topological superconductivity hosts protected quasiparticles and is central to topological quantum computation, yet its realization in intrinsic materials remains challenging and often relies on engineered platforms. Here we uncover a symmetry-constrained mechanism for nodal topological superconductivity in altermagnets. Focusing on fourfold rotational collinear altermagnets, we show that the native crystalline antiunitary symmetry $\mathcal{T}C_{4z}$ generically forbids pure spin-singlet pairing and selects pairing structures that admit Bogoliubov-de Gennes (BdG) Hamiltonians with emergent chiral symmetries. These symmetries further give rise to robust nodal topological phases over broad parameter regimes, including a nodal-point phase hosting Majorana flat bands (MFBs) and two distinct nodal-loop phases with chiral Majorana edge states. Notably, the nodal structure persists even after spontaneous breaking of the antiunitary symmetry, indicating that the topology originates from symmetry-constrained pairing rather than direct symmetry protection. Finally, we propose tunneling signatures that can distinguish these nodal phases and probe symmetry breaking experimentally.