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Center for Nonlinear Studies |
Complex oxides have emerged as one of the most important platforms for the discovery of new phenomena in condensed matter physics. The extraordinarily diverse physical behavior displayed by these materials is due in large part to the acute competition between the various degrees of freedom, which leads to a subtle energy balance between possible ground states. It is perhaps unsurprising that under these conditions, particularly in randomly doped materials, electronic inhomogeneity is ubiquitous. Magneto-electronic phase separation, where multiple electronic and magnetic phases coexist spatially, even in the absence of chemical segregation, has been observed in a variety of materials and is widely believed to be electronically-driven. In this talk I will elaborate on the features of the doped perovskite cobaltites (e.g. La1-xSrxCoO3) which make them model systems for the study of this nanoscopic phase separation. We have used bulk crystals of these materials to study the phenomenology, consequences, and origins of the magnetically phase-separated state, mostly by neutron scattering, electronic transport, and heat capacity. Our primary conclusions are that (i) the spontaneous magnetic nanostructuring has interesting consequences including the existence of giant magnetoresistance-type effects in a bulk solid1, and (ii) the magnetic phase separation is driven purely by the local doping fluctuations that are inevitable at these length scales2. In essence the nanoscale inhomogeneity is doping fluctuation-driven rather than electronically-driven, challenging the commonly accepted electronic phase separation scenario. The talk will be concluded with brief comments on more recent work on interface-induced magnetic phase separation in La1-xSrxCoO3 heterostructures3, and its interplay with strain-driven oxygen vacancy ordering 4.
Host: Marc Janoschek