报告题目：Hidden Phases Revealed at the Surface of Layered Transition Metal Compounds

报 告 人：Ward Plummer，Louisiana State University

报告时间：2016年6月15日16：00

报告地点：理科楼C302

报告摘要：Complexity in transition-metal compounds originates for the close and nonlinear coupling of spin, charge, orbital, and lattice degrees of freedom. Creating a surface disturbs the balance between these degrees of freedom, and in many cases results in phased Hidden in the bulk. Several examples will be presented to illustrate this phenomenon. 1) Dynamic antiphase spin domain walls have been proposed for the parent compound of the Fe based super-conductor BaFe₂As₂. The surface (√2x√2) R45^ophase displays a coupled structural-magnetic antiphase domain walls with a reduced symmetry compared to the bulk. 2) The (1x2) surface phase Ca(Fe_1-xCo_x)₂stabilizes Antiferromagnetic Ordering leading to the coexistence of superconductivity and antiferromagnetic ordering. 3) The final example is for Mn doped double-layer Ruthenate Sr₃(Ru_1-xMn_x)₂O₇, where the surface phase diagram is almost opposite from the bulk due to surface induced tilt of the octahedral in the parent compound. The surface of Sr₃(Ru_0.84Mn_0.16)₂O₇is metallic while the bulk is insulating, because the surface tilt has been removed.