| The 5d-transition metal oxides have become a fertile ground for studies of new physics driven by spin-orbit interaction. It is commonly expected that iridium oxides are more metallic and less magnetic than their 3d and 4f counterparts because of the extended nature of the 5d orbitals. In marked contrast, many iridates are magnetic insulators that exhibit a large array of phenomena seldom or never seen in other materials. In this talk, we review the anomalous physical properties of the iridates, and then focus on the novel phenomena we have recently observed in the layered iridates Srn+1IrnO3n+1 (n=1 and 2). The critical underlying mechanism for these phenomena is the spin-orbit interaction or the energy-splitting effect, which strongly competes with other interactions to create an unusual balance between relevant degrees of freedom in this class of materials. |
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