Observation of superconductivity in a nontrivial $\mathcal{Z}_2$ approximant quasicrystal

TL;DR

This paper reports the discovery of superconductivity in a quasicrystal approximant with nontrivial topological electronic states, revealing a new platform for studying unconventional superconductivity in aperiodic materials.

Contribution

It presents the first observation of superconductivity in a quasicrystal approximant with nontrivial $ ext{Z}_2$ topology and detailed analysis of its electronic structure.

Findings

Superconductivity observed at ~5.47 K in Al$_{13}$Os$_{4}$.

Nontrivial $ ext{Z}_2=1$ topological state with spin-polarized surface states.

Presence of saddle point van Hove singularities at the Fermi level.

Abstract

Superconductivity and nontrivial topology are highly sought-after phenomena in quantum materials. While many topological crystalline materials have been found to exhibit superconductivity, their presence in quasicrystals - materials with a unique aperiodic yet ordered structure - has remained largely unexplored. In this work, we report the discovery of superconductivity in a monoclinic approximant to the decagonal quasicrystal Al$_{13}$Os$_{4}$, that exhibits a high superconducting transition temperature and a nontrivial electronic structure. The resistivity, magnetization, specific heat, and $\mu$SR measurements confirm superconductivity with a critical temperature of $\sim5.47$ K. Detailed electronic structure and symmetry analysis reveal nontrivial state with $\mathcal{Z}_{2}=1$ and spin-polarized conducting surface states. Importantly, we identify three-dimensional saddle point van Hove singularities with substantial flat energy dispersion at the Fermi level, which can enhance superconductivity. Our results highlight a rich interplay between superconductivity and nontrivial electronic states in Al$_{13}$Os$_{4}$, demonstrating it as a unique platform for exploring unconventional superconducting states in quasicrystalline materials.