Evidence of Hidden Magnetic Order in non-centrosymmetric Weyl semimetal GdAlSi*

In recent decades, spintronics has emerged as a compelling alternative to traditional electronics. The discovery of topological phases of matter characterized by safeguarded spin-polarized states has introduced exciting possibilities. Concurrently, there has been a recent revelation of intriguing non-relativistic spin splitting in collinear antiferromagnetic materials possessing specific symmetries.

This study unveils the coexistence of these two remarkable phases within a single material, GdAlSi. GdAlSi adopts a body-centered tetragonal structure with a non-centrosymmetric space group, denoted as I4₁md (109). Magnetization data reveals antiferromagnetic ordering with a critical temperature (T_N) of 32 K.

Ab-initio calculations establish GdAlSi as a collinear antiferromagnetic Weyl semimetal, featuring an unconventional, momentum-dependent spin splitting, often referred to as "altermagnet." Angle-resolved photoemission spectroscopy measurements conducted on GdAlSi single crystals subsequently affirm the presence of Fermi arcs-like feature, a distinctive hallmark of Weyl semimetals. Electric and magnetic multipole analysis deepens our understanding of the symmetry-mediated, momentum-dependent spin splitting, which possesses a strictly non-relativistic origin.

To the best of our knowledge, the coexistence of unconventional antiferromagnetic order and non-trivial topology in a single material, as observed in GdAlSi, represents a groundbreaking discovery unprecedented in any material. This uniqueness positions GdAlSi as a promising material for topotronic applications.