Nuclear magnetic resonance study of the electron doped Dirac-Mott Insulator double perovskite Ba2Na(1-x)CaxOsO6

Osmium-based materials exhibit unconventional magnetism due to the interplay between spin orbit coupling and strong electronic correlations. In this thesis we investigate for the first time the effect of charge doping on the Dirac Mott insulator double perovskites Ba2Na(1-x)CaxOsO6 by using Nuclear Magnetic Resonance technique. We study in details the evolution of the magnetic phase diagram as a function of doping and applied magnetic field. The system rapidly evolves from a canted to a collinear antiferromagnetic ground state with a monotonic increase of the magnetic transition temperature. Furthermore, the system remains insulating in the whole range of doping, despite the injection of extra electrons. This indicates that the Dirac-Mott insulating state of this material is unusually robust. In particular, the results show an unexpected thermally activated charge dynamics which suggests the presence of polarons dominating the high temperature excitations of this Dirac-Mott insulator.