Title

Emergent phenomena in transition metal oxides

Speaker

Prof. Hanghui Chen

NYU-ECNU Institute of Physics

New York University Shanghai

Time

10：00am, December 25, 2018

Place

Room 9004 at the HFNL building

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.

Abstract

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.