Periodic Reporting for period 1 - UFOX (Unveiling complexity in Functional hybrid OXides)
Periodo di rendicontazione: 2015-05-25 al 2017-05-24
The main objectives of UFOX are: i) determination of the magnetic and orbital orders in hybrid oxides, ii) impact of doping on the pure 4d (3d) oxides and on the electronic transport properties, iii) analysis and modeling of the electronic and transport properties and X-ray based spectroscopic outcomes on 3d-4d hybrids and 3d-4d heterostructures.
Such results allowed to revisit the concept of band and Mott insulators as well as superconductors and conventional metals in view of their topological behaviour. The search for topological phases of matter and, more specifically, the occurrence of non-Abelian states set remarkable challenges both for fundamental physics and the development of innovative solutions in quantum engineering. The investigation of TM substitution guided the general idea that, though harmful for some types of topological protections, inhomogeneous perturbations can open a completely different perspective in the area of topological matter because they represent a rich intrinsic source of topological phases or topological transitions. Taking the d(2)-d(4) exchange and motivated by this innovative outlook, we face a new route to get Majorana end modes in low-dimensional spin-orbital systems with spatially inhomogeneous anisotropic exchange. Apart from the impact on the targeted materials, such study provides a general correspondence between inhomogeneous spin-orbital exchange and itinerant systems with a distribution of pairing centers. The investigation of the phase diagram indicates how different types of orbital exchange interfere to yield topological transitions and domains in the parameter space that are robust to local variations of the dopant configuration. This result is novel, general, and can have significant impact both on the generation and on the manipulation of topological modes in the presence of disorder by suitably modifying the host or the dopant configuration.
Concerning the d(3)-d(4) hybrids, on a general ground the competition of ferromagnetic and antiferromagnetic exchanges for orbital directional correlated systems leads to distinct antiferromagnetic order which is robust to doping and relevant for addressing the observed physical phase diagram in Mn-doped bilayered ruthenates. Taking the paradigmatic example of zig-zag antiferromagnetic patterns arising in doped multi-orbital electron systems, we successfully demonstrate the occurrence of magnetic Dirac semimetal phases in systems with strong spin-orbital-charge entanglement and dictated by new symmetry conditions.
Indeed, we identify novel topological semimetal and metal phases in a large variety of non-symmorphic collinear antiferromagnets with glide reflection symmetry, a combination of mirror and half-lattice translation. Taking into account the intrinsic glide symmetry of the zig-zag antiferromagnetic order we find metal-insulator transitions and semimetal phases made of Dirac points having multiple symmetry-protection as well as with triple and quadruple band-crossing points. Such phases occur when driving the transition between different types of insulator due to magnetic exchange and spin-orbit coupling. The study can have a high impact in various class of materials as zig-zag antiferromagnets represent a common and ubiquitous realization of magnetic order in a large variety of TMOs as experimentally demonstrated in ruthenates, manganites, dichalcogenides, iridates, and nickelates. Thus, besides providing a new perspective of ordered states in complex materials, these findings indicate that topological gapless phases may occur in a wide area of interacting magnetic systems.