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The realization of fourfold anisotropic magnetoresistance (AMR) in 3d-5d heterostructures has boosted major efforts in antiferromagnetic (AFM) spintronics. However, despite the potential of incorporating strong spinorbit coupling, only small AMR signals have been detected thus far, prompting a search for mechanisms to enhance the signal. In this paper, we demonstrate an extraordinarily elevated fourfold AMR of 70% realized in CaMnO3/CaIrO3 thin film superlattices.We find that the biaxial magnetic anisotropy and the spin-flop transition in a nearly Mott insulating phase form a potent combination, each contributing one order of magnitude to the total signal. Dynamics between these phenomena capture a subtle interaction of pseudospin coupling with the lattice and external magnetic field, an emergent phenomenon creating opportunities to harness its potential in AFM spintronics.

In some metals containing a sub-lattice of rare earth or actinide ions, free local $f$ spins at high temperatures dissolve into the sea of quantum conduction electrons at low temperatures, where they become mobile excitations. Once mobile, the spins acquire charge, forming electrons of heavy mass, known as heavy fermions. In turn, the incorporation of heavy charges into the conduction sea leads to an increase in the volume of the Fermi surface. This process, called Kondo scattering, is accompanied by a dramatic, temperature dependent transformation of the electronic interactions and masses. Since the Kondo phenomena is controlled by quantum fluctuations, here we ask, at which point does the Fermi surface change character? A priori, the answer is not clear, since near its onset, the Kondo effect cannot be described as a simple hybridization of electronic eigenstates. Conventional descriptions of this Kondo scattering process consider that hybridization, Fermi volume change, and $f$-electron mobility occur simultaneously. However, using angle resolved photoemission spectroscopy to measure the evolution of excitations, we find that the changes of the Fermi surface emerge at temperatures an order of magnitude higher than the opening of the hybridization gap, and two orders of magnitude higher than the onset of the coherent character of the $f$-electrons. We suggest that the large changes in Fermi volume, driven by electronic fluctuations, occur at temperatures where the various $\Gamma_x \to \Gamma_y$ crystal field-split $f$ levels become accessible to conduction states of the corresponding symmetries. The separation of these energy scales significantly modifies the conventional description of the Kondo lattice effect, which still lacks a full theoretical description., Comment: Manuscript originally submitted to a peer-reviewed journal on February 27, 2015; please contact corresponding author for more details

International audience; The changes in the electronic structure of V2O3 across the metal-insulator transition induced by temperature, doping and pressure are identified using high resolution x-ray absorption spectroscopy at the V pre K-edge. Contrary to what has been taken for granted so far, the metallic phase reached under pressure is shown to differ from the one obtained by changing doping or temperature. Using a novel computational scheme, we relate this effect to the role and occupancy of the a1g orbitals. This finding unveils the inequivalence of different routes across the Mott transition in V2O3