Unconventional anomalous Hall effect in epitaxially stabilized orthorhombic Ru$^{3+}$ perovskite thin films

Complex oxides are mesmerizing material systems to realize multiple physical properties and functionalities by integrating different elements in a single compound. However, owing to the chemical instability, not all the combinations of elements can be materialized despite the intriguing potential expected from their magnetic and electronic properties. In this study, we demonstrate an epitaxial stabilization of orthorhombic Ru$^{3+}$ perovskite oxides: LaRuO$_3$ and NdRuO$_3$, and their magnetotransport properties that reflect the difference between non-magnetic La$^{3+}$ and magnetic Nd$^{3+}$. Above all, an unconventional anomalous Hall effect accompanied by an inflection point in magnetoresistance is observed around 1.3 T below 1 K for NdRuO$_3$, which is ascribed to topological Hall effect possibly due to a non-coplanar spin texture on Nd$^{3+}$ sublattice. These studies not only serve a new testbed for the interplay between spin-orbit coupling and Coulomb interaction but also open a new avenue to explore topological emergent phenomena in well-studied perovskite oxides.