2013/05/31 by William Witczak-Krempa, Gang Chen, Yong Baek Kim +1 · 2 citations
Physics and Astronomy · #cond-mat.str-el #cond-mat.mes-hall #cond-mat.mtrl-sci #cond-mat.supr-con
paper · pdf · doi:10.1146/annurev-conmatphys-020911-125138
published as Annual Review of Condensed Matter Physics, Vol. 5: 57-82 (2014) · 35p, 7 figs, Invited review article (Ann. Rev. Cond. Mat. Phys.). v2: Improvements throughout, added references
arxiv created 2014/03/12 · arxiv updated 2014/03/14
We discuss phenomena arising from the combined influence of electron correlation and spin-orbit coupling, with an emphasis on emergent quantum phases and transitions in heavy transition metal compounds with 4d and 5d elements. A common theme is the influence of spin-orbital entanglement produced by spin-orbit coupling, which influences the electronic and magnetic structure. In the weak-to-intermediate correlation regime, we show how non-trivial band-like topology leads to a plethora of phases related to topological insulators. We expound these ideas using the example of pyrochlore iridates, showing how many novel phases such as the Weyl semi-metal, axion insulator, topological Mott insulator, and topological insulators may arise in this context. In the strong correlation regime, we argue that spin-orbital entanglement fully or partially removes orbital degeneracy, reducing or avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the honeycomb lattice iridates and double perovskites, this leads to enhanced quantum fluctuations of the spin-orbital entangled states and the chance to promote exotic quantum spin liquid and multipolar ordered ground states. Connections to experiments, materials, and future directions are discussed.