Rutgers Center for Emergent Materials
Rutgers University, Piscataway, USA

个人简介
Sang-Wook Cheong obtained his Bachelor (mathematics, 1982) from Seoul National University, and Ph. D (Physics, 1989) from University of California, Los Angeles. He worked at Los Alamos National Laboratory for 1986-1989, and was a member of technical staff at Bell Laboratories (1989-2001). Since 1997, he has been a professor at Rutgers University. He became the founding director of Rutgers Center for Emergent Materials (2005-). His scientific field has been the physics of complex oxides, including multiferroics, colossal magnetoresistive oxides and high Tc superconductors.
Cheong became a fellow of American Physical Society in 2000, and has received a number of awards: Board of Trustees Award for Excellence in Research at Rutgers University (2003), Ho-Am Prize in Science from Samsung (2007), and KBS Global Korean Award (2009). He is currently a Divisional Associated Editor for Physical Review Letters, a Distinguished Professor at Pohang Science and Technology University, Korea, and a Distinguished Visiting Scholar, National Synchrotron Radiation Research Center, Taiwan.

Abstract
Hexagonal REMnO₃ (RE= rare earths) with RE=Ho-Lu, Y, and Sc, is an improper ferroelectric where the size mismatch between RE and Mn induces a trimerization-type structural phase transition, and this structural transition leads to ferroelectricity. For the last two decades, ferroelectric REMnO3 has been extensively studied as a candidate material for ferroelectric memories and also for its multiferroicity – the coexisting nature of ferroelectricity and magnetism. Despite this research the true ferroelectric domain structure and its relationship with structural domains have never been revealed. Using transmission electron microscopy and conductive atomic force microscopy, we have investigated the relationship among trimerization antiphase domains, ferroelectric domains and antiferromagnetic domains in REMnO3. We found that ferroelectric domain walls and structural antiphase boundaries are mutually interlocked. In addition, we discovered a vortex structure with six domains emerging from one point - all distinctly characterized by polarization orientation, structural antiphase, and antiferromagnetic  relationships. This vortex can be considered as a topological defect in a multiferroic. We also found that ferroelectric domains and walls have distinct electronic transport properties. These fascinating results reveal the rich physics of the hexagonal system with a truly-semiconducting band gap where structural trimerization, ferroelectricity, magnetism, and charge conduction are intricately coupled.

联 系 人：李 泓 研究员（82648067）