Exploring Eu₅In₂Sb₆, a non-symmorphic antiferromagnetic insulator: from macroscopic to atomic length scales

We combine STM/STS with bulk measurements to investigate the Zintl phase Eu₅In₂Sb₆, a non-symmorphic antiferromagnetic insulator. This research was motivated by the theoretical predictions of non-trivial Fermi surface topology stabilized by non-symmorphic symmetry.

Eu₅In₂Sb₆ crystallizes in an orthorhombic structure (Pbam), characterized by infinite [In₂Sb₆]¹⁰⁻ double chains along the c-axis. At low temperatures, two magnetic transitions (T_N1 ≈ 14 K and T_M2 ≈ 7 K), revealed in our magnetic and transport measurements, point to an intricate magnetic structure. Interestingly, the reported emergence of colossal magnetoresistance (CMR) suggests the formation of magnetic polarons¹.

Performing STM/STS measurements, we obtained local insight into the electronic structure and surface morphology. The samples were cleaved in situ in UHV and at low temperatures. In the (010) plane, we obtained striped patterns that can be correlated to the stacking of double-chains. The attempted cleavage along the a-axis revealed a more complex pattern, which could be indicative of cleavage along the (1-10) plane. So far, direct experimental evidence of topological surface states remains elusive.

[1] P. Rosa et al., npj Quantum Materials (2020) 5:52.