Transition metal oxides exhibit a wide range of exotic phenomena from metal-insulator transition, colossal magnetoresistance to high-temperature superconductivity. In this talk, we focus on one important class of transition metal oxides, namely double perovskite oxides. We show that: i) a magnetic transition (from paramagnetic to long-range magnetically ordered) can simultaneously induce an orbital-selective insulator-metal transition in rock-salt ordered double perovskite oxides A2BB'O6 where B is a non-magnetic ion and B' a magnetic ion with a d3 electronic configuration (Ru5+ and Os5+). The orbital selectivity originates from geometrical frustration of a face-centered-cubic lattice on which the magnetic ions B' reside; ii) double perovskite oxide BiPbTi2O6 is a polar metal. The mechanism is that 6s lone-pair electrons in Bi and Pb ions tend to favor off-center displacements; on the other hand, Bi and Pb have different formal valences and charge imbalance leads to conducting electrons. At the interface between polar metal BiPbTi2O6 and insulating ferroelectrics, there is a strong structural coupling such that using an electric field to switch the polarization in the ferroelectrics can simultaneously flip the in-plane polar displacements in BiPbTi2O6 by 180 degrees.
Dr. Hanghui Chen is an Assistant Professor of Physics of NYU Shanghai and a Global Network Assistant Professor of NYU. Prior to joining NYU Shanghai, he was a post-doctoral fellow at Columbia University. He holds a Ph.D from Yale University and a B.S. from Peking University. Dr. Chen’s research interests lie in first-principles modelling and design of complex meta-materials, in particular transition metal oxides and their heterostructures.