$π$/4 phase shift in the angular magnetoresistance of infinite layer nickelates

Abstract: The discovery of superconductivity in nickelates has generated significant interest in condensed matter physics. Nickelate superconductors, which are hole-doped within the layered structure of RNiO$_2$, share structural similarities with high-$T_c$ cuprate superconductors. However, despite similarities in formal valence and crystal symmetry, the fundamental nature of the superconducting state and the parent compound phase in nickelates remains elusive. Strong electronic correlations in infinite-layer nickelates suggest a potentially complex phase diagram, akin to that observed in cuprates, yet a key question about the magnetic ground state remains unanswered. Through magnetoresistance measurements across varying field strengths and orientations, we observe distinct angular-dependent magnetoresistance (AMR) oscillations with four-fold symmetry. Notably, this four-fold symmetry displays a $\pi/4$ phase shift with doping or applied magnetic field. Our findings parallel behaviors in electron-doped cuprates, suggesting that a static or quasi-static magnetic order exists in the infinite-layer nickelates, echoing characteristics of electron-doped cuprates. Furthermore, our modeling of the system reveals that the AMR is directly related to the underlying antiferromagnetic order, reinforcing this interpretation.