Anisotropic magnetoresistance in spin–orbit semimetal [Formula: see text]

[Formula: see text] , the three-dimensional member of the Ruddlesden–Popper iridates, is a paramagnetic semimetal characterised by a the delicate interplay between spin–orbit coupling and Coulomb repulsion. In this work, we study the anisotropic magnetoresistance (AMR) of [Formula: see text] thin films, which is closely linked to spin–orbit coupling and probes correlations between electronic transport, magnetic order and orbital states. We show that the low-temperature negative magnetoresistance is anisotropic with respect to the magnetic field orientation, and its angular dependence reveals the appearance of a fourfold symmetric component above a critical magnetic field. We show that this AMR component is of magnetocrystalline origin, and attribute the observed transition to a field-induced magnetic state in [Formula: see text] . ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1140/epjp/s13360-020-00613-3) contains supplementary material, which is available to authorized users.