Condensed-Matter Physics & Materials Science Seminar
"Exploring the spin-orbit entanglement in 5d layered perovskites with x-ray resonant scattering techniques"
Presented by Stefano Boseggia, Univ. College London & Diamond Light Source Ltd., United Kingdom
Tuesday, February 4, 2014, 1:30 pm
Bldg. 734, ISB Conference 201 (upstairs)
Hosted by: John P. Hill
Transition metal oxides (TMO) containing a 5d element are increasingly attracting attention as an arena in which to search for novel electronic states. These are proposed to derive from the strong spin-orbit interaction (SOI) in the 5d's, which in essence entangles spin and orbital moments, strongly mixing spin and spatial coordinates. Iridium based compounds have featured predominantly in this quest, with considerable focus on the layered perovskites of which Sr2IrO4 is the prototypical example. In this case, the SOI leads to a Jeff = 1/2 ground state for the Ir4+ (5d5) ions, from which a Mott-like insulator then emerges through the action of relatively weak electronic correlations which would otherwise lead to a metallic state. Direct evidence for the existence of a Jeff = 1/2 ground state in the single-layer Sr2IrO4 was provided by x-ray resonant magnetic scatting (XRMS) experiments which revealed a much stronger resonance at the L3 edge than at the L2. X-ray resonant scattering is indeed a valuable technique to have a direct access to the 5d magnetic orbitals via strong dipole-dipole transitions. In this talk we will first review the magnetic and the electronic properties of the Jeff = 1/2 ground state observed in Sr2IrO4 .We then show the evolution of this state as a function of the dimensionality in Sr3Ir2O7 , the bilayer cousin of Sr2IrO4 , and as a function of local symmetry changes in the single-layer Ba2IrO4 . We conclude that, due to the unique three-dimensional character of the Jeff =1/2 state produced by the strong SOI, both the magnetic and electronic structures in the layered perovskites are remarkably robust to structural distortions, whereas they show unusual changes as a function of the dimensionality. Finally we will present our latest calculation of the XRMS cross section in layered iridates  and our reinterpretation, accompanied with novel RIXS data, of magnetism in Sr3Ir2O7. References 1. Kim, B. J., e