We report new observation of cooperative paramagnetic fluctuations of Ru 4+ spins that coexist with the non-Fermi liquid state in CaRuO3 perovskite below T 22 K. Detailed electrical, magnetic and neutron scattering measurements reveal that the Ru 4+ ions reside in magnetic field independent random domains with dynamic properties that are reminiscent of the cooperative paramagnetic fluctuations. The linear (E/T ) scaling of the dynamic susceptibilities and divergence of the mean relaxation time as T → 0 K suggest quasi-local critical nature of the spin fluctuations. We argue that the non-Fermi liquid behavior arises due to the quantum critical nature of the cooperative paramagnetic fluctuations in CaRuO3.

We report on the study of insulator-to-metal transition in post-perovskite compound CaIrO3. It is discovered that a gradual chemical substitution of calcium by yttrium leads to the onset of strong metallic behavior in this compound. This observation is in stark contrast to BaIrO3, which preserves its Mott insulating behavior despite excess of charge carriers due to yttrium doping. Magnetic measurements reveal that both compounds tend to exhibit magnetic character irrespective of the chemical substitution of Ca or Ba. We analyze these unusual observations in light of recent researches that suggest that CaIrO3 does not necessarily possess j = 1/2 ground state due to structural distortion. The insulator-to-metal transition in CaIrO3 will spur new researches to explore more exotic ground state, including superconductivity, in post-perovskite Mott insulators. 1-5 One recent proposal has suggested the application of 5d iridium oxide compound in the spincurrent detection.6 The ground state in majority of these materials, A 2 IrO 3 and BIrO 3 (where A = alkali metals and B = alkaline earth metals), is often described as a Mott insulting state, where the Ir 4+ ion with a (t 2g ) 5 electronic configuration splits into a fully occupied j = 3/2 state and a half-filled j = 1/2 states. 7-11 While the quantum-mechanical nature of the spin-orbit coupling is considered key to the quantum Hall effect in topological insulating materials, 12 its interaction with cubic crystal field in Ir 5d transition element ensures a j = 1/2 ground state in Mott insulator iridates. 10,13,14 The bandwidth of the j = 1/2 state w N t, where N is the coordination number and t is the Ir-Ir hopping matrix, is found to be comparable to the Coulomb repulsion potential U in BIrO 3 ; thus on the verge of attaining the metallic character.15 A simple modification in the structural properties or, the change in the hopping integral achieved via higher carrier density can, therefore, induce a highly desirable metallic behavior in iridium oxide compounds of 1-1-3 phase.In this letter, we present new results on the presence (absence) of insulator-to-metal transition in the holedoped CaIrO 3 (BaIrO 3 ). In a novel observation, it is found that the yttrium substitution of calcium leads to an onset of metallic behavior at x = 0.4 in Y x Ca 1−x IrO 3 , which is not the case in Y x Ba 1−x IrO 3 . Both compounds, however, preserve magnetic characteristic irrespective of the chemical doping. In another notable observation, the dimensionality analysis of the electrical transport data below the magnetic transition demonstrates a quasi-2D electronic pattern (d = 2.4) in CaIrO 3 , which is in stark contrast to 3D electronic transport in BaIrO 3 . CaIrO 3 and BaIrO 3 manifest Mott insulating behavior with charge gap of 0.17 eV and 50 meV, respectively. 11,16 While CaIrO 3 crystallizes primarily in the orthorombic phase of crystallographic group Cmcm (similar to MgSiO 3 ),17 BaIrO 3 forms a monoclinic structure (C2/m).9 In both compounds, the chemical structure is composed of...

Quantum magnetic properties in a geometrically frustrated lattice of spin‐1/2 magnet, such as quantum spin liquid or solid and the associated spin fractionalization, are considered key in developing a new phase of matter. The feasibility of observing the quantum magnetic properties, usually found in geometrically frustrated lattice of spin‐1/2 magnet, in a perovskite material with controlled disorder is demonstrated. It is found that the controlled chemical disorder, due to the chemical substitution of Ru ions by Co‐ions, in a simple perovskite CaRuO3 creates a random prototype configuration of artificial spin‐1/2 that forms dimer pairs between the nearest and further away ions. The localization of the Co impurity in the Ru matrix is analyzed using the Anderson localization formulation. The dimers of artificial spin‐1/2, due to the localization of Co impurities, exhibit singlet‐to‐triplet excitation at low temperature without any ordered spin correlation. The localized gapped excitation evolves into a gapless quasi‐continuum as dimer pairs break and create freely fluctuating fractionalized spins at high temperature. Together, these properties hint at a new quantum magnetic state with strong resemblance to the resonance valence bond system.

Magnetic fluctuations in transition metal oxides are a subject of intensive research because of the key role they are expected to play in the transition from the Mott insulator to the unconventional metallic phase of these materials, and also as drivers of superconductivity. Despite much effort, a clear link between magnetic fluctuations and the insulator-to-metal transition has not yet been established. Here we report the discovery of a compelling link between magnetic fluctuations and the insulator-to-metal transition in Ca(Ir1−xRux)O3 perovskites as a function of the substitution coefficient x. We show that when the material turns from insulator to metal, at a critical value of x ~ 0.3, magnetic fluctuations tend to change their character from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant electron state with Hund’s orbital coupling. These results are expected to have wide-ranging implications for our understanding of the unconventional properties of strongly correlated electrons systems.

Artificial magnetic honeycomb lattices are expected to exhibit a broad and tunable range of novel magnetic phenomena that would be difficult to achieve in natural materials, such as long-range spin ice, entropy-driven magnetic charge-ordered state and spin-order due to the spin chirality. Eventually, the spin correlation is expected to develop into a unique spin solid state density ground state, manifested by the distribution of the pairs of vortex states of opposite chirality. Here we report the creation of a new artificial permalloy honeycomb lattice of ultra-small connecting bonds, with a typical size of 12 nm. Detail magnetic and neutron scattering measurements on the newly fabricated honeycomb lattice demonstrate the evolution of magnetic correlation as a function of temperature. At low enough temperature, neutron scattering measurements and micromagnetic simulation suggest the development of loop state of vortex configuration in this system. arXiv:1802.06631v1 [cond-mat.mes-hall]