GdAlSi: An antiferromagnetic topological Weyl semimetal with nonrelativistic spin splitting

Spintronics has emerged as a viable alternative to traditional electronics-based technologies in the past few decades. While the discovery of topological phases of matter with protected spin-polarized states has opened up exciting prospects, recent revelation of intriguing nonrelativistic spin-splitting in antiferromagnetic (AFM) materials with unique symmetries facilitate a wide possibility of realizing both these features simultaneously. In this work, we report the coexistence of these two intriguing properties within a single material: GdAlSi. Single crystal of GdAlSi stabilizes in a body-centered tetragonal structure with a noncentrosymmetric space group $I{4}_{1}md$ (109), which is confirmed using detailed structural analysis through x-ray diffraction (XRD) and optical second harmonic generation (SHG) measurements. The magnetization data indicates AFM ordering with an ordering temperature (${T}_{N}$) $\ensuremath{\sim}32$ K. Ab initio calculations reveal GdAlSi to be a collinear AFM Weyl semimetal with an unconventional, momentum-dependent spin-splitting, also referred to as altermagnet. Angle-resolved photoemission spectroscopy measurements on GdAlSi single crystals subsequently hints the possible presence of Fermi arcs. Electric and magnetic multipole analysis provides a deeper understanding of the symmetry-mediated, momentum-dependent spin-splitting, which has strictly nonrelativistic origin. GdAlSi is possibly the first candidate material with noncentrosymmetric collinear AFM structure showing such momentum-dependent spin-splitting, as also confirmed by our detailed symmetry analysis, rendering GdAlSi a special and promising candidate material. We further propose a device harnessing these features, poised to enable practical and efficient topotronic applications.