Antiferromagnetism-driven two-dimensional topological nodal-point superconductivity

TL;DR

This paper reports the experimental discovery of a gapless topological nodal-point superconductor driven by antiferromagnetic order in monolayer systems, confirmed by scanning tunneling microscopy and theoretical calculations.

Contribution

It demonstrates that antiferromagnetism can induce a 2D topological superconducting phase, providing a new approach to designing topological quantum materials.

Findings

Observation of low-energy edge modes at antiferromagnetic boundaries

Confirmation of topological phase driven by AFM order through calculations

Dependence of edge mode spectral weight on atomic edge configuration

Abstract

Magnet$/$superconductor hybrids (MSHs) hold the promise to host emergent topological superconducting phases. Both one-dimensional (1D) and two-dimensional (2D) magnetic systems in proximity to s-wave superconductors have shown evidence of gapped topological superconductivity with zero-energy end states and chiral edge modes. Recently, it was proposed that the bulk transition-metal dichalcogenide 4Hb$-$TaS$_2$ is a gapless topological nodal-point superconductor (TNPSC). However, there has been no experimental realization of a TNPSC in a MSH system yet. Here we present the discovery of TNPSC in antiferromagnetic (AFM) monolayers on top of an s-wave superconductor. Our calculations show that the topological phase is driven by the AFM order, resulting in the emergence of a gapless time-reversal invariant topological superconducting state. Using low-temperature scanning tunneling microscopy we observe a low-energy edge mode, which separates the topological phase from the trivial one, at the boundaries of antiferromagnetic islands. As predicted by the calculations, we find that the relative spectral weight of the edge mode depends on the edge's atomic configuration. Our results establish the combination of antiferromagnetism and superconductivity as a novel route to design 2D topological quantum phases.