Emergent transport properties on the verge of metal-insulator transitions in pyrochlore 5d/4d oxides*

Magnetic Weyl semimetals have been proved to generate emergent transport properties such as giant anomalous Hall effect due to the band-crossing points acting as magnetic monopoles of Berry curvature.
A variety of 5d/4d oxides, in which the magnitude of the relativistic spin-orbit coupling is comparable to that of the electron correlation, are suggested to host such a topologically-nontrivial property. For instance, pyrochlore iridates (R₂Ir₂O₇) are firstly proposed as a candidate for the magnetic Weyl semimetal. Recent studies uncover that Nd₂Ir₂O₇ shows salient magnetotransport properties on the verge of metal-insulator transitions, attributable to the realization of multiple topological semimetals with different magnetic ordering patterns. Here, we report another examples of such states in Pr₂Ir₂O₇, which is known as a paramagnetic Luttinger semimetal. The resistivity is largely enhanced in the 3-in 1-out magnetic configuration of Pr-4f moments, whereas it is relatively small in the magnetically metastable state (so-called Kagome-ice state) accompanied with the plateau structure of Hall resistivity. It indicates that the quadratic-band-touching electronic structure is significantly sensitive to the localized magnetic configurations even in the weak-coupling system.
We also demonstrate that the pyrochlore 4d oxides provide a fertile playground. Particularly, Ruthenates (A²⁺₂Ru⁵⁺₂O₇: 4d³or R³⁺₂Ru⁴⁺₂O₇: 4d⁴) exhibit wide range of magnetic/electronic phases from an antiferromagnetic insulator to a ferromagnetic-like metal as the valence of A site changes. Furthermore, the sizable anomalous Hall conductivity is observed in the intermediate A-site composition, which can be understood in the context of the topological nature of the band structures.