(Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, USA）
Two-dimensional electron gases (2DEGs) at the interfaces or surfaces of band insulating SrTiO3 (STO) (001) have displayed many emergent phenomena such as quantum Hall effects, superconductivity, and ferromagnetism, which are not only important for basic research, but also for realizing oxide electronics. These properties are largely governed by the structures of Ti 3d band as well as Rashba spin-orbit coupling at the surface or interface. One of the anomalous behaviors is the in-plane anisotropic magnetoresistance (AMR) which does not normally occur in metallic systems. In this talk, I will present our results on untangling the effects of band filling and electric field on the AMR in (111)-, (110)-, and (001)-oriented STO surface 2DEGs using a special gating sequence. We created states with different carrier concentrations but without a gating electric field and states with different electric fields but constant carrier density. We also applied current along different directions to subtract the Lorentz Force contributions. To our surprise, the AMR symmetries of (111)-, (110)-, and (001)-oriented 2DEGs exhibit dramatically different responses to the tuning of band filling, which perfectly match the symmetries of the surface electron band orbitals at corresponding filling levels determined by ARPES measurements. On the other hand, the AMR symmetries of all three orientations show similar response to the tuning of electric field. I will discuss the possible origin and the implication of the effect where the AMR symmetry matches the surface band orbital symmetry in 2DEGs with spin-orbit coupling.
Qi Li is a professor at Department of Physics and Institute of Materials Research, Pennsylvania State University. Her current research interest is primarily in the areas of topological insulators and superconductors in nanostructures, and multiferroic, spintronics, and two-dimensional electron gases in complex oxide systems, especially at interfaces. She graduated from Peking University and was a visiting scholar at KFK, Germany. She was a postdoc at Bellcore laboratory in New Jersey and assistant research scientist at Center for Superconductivity research at University of Maryland before joining Penn State as an assistance professor in 1995. She became a full professor in 2004. She has published more than 200 journal articles and is the recipient of NSF Career award among other awards. She is a fellow of American Physical Society.