Abstract:
The integer quantum Hall effect (IQHE), first found in 1980, is one of the most important discoveries in condensed matter physics. When a strong perpendicular magnetic field is applied to a 2D electron gas at low temperatures, the Hall conductance is precisely quantized in the fundamental conductance quantum (e2/h) due to Landau-level quantization. This quantization was soon found to be connected with the topologically nontrivial 2D insulating band structure, characterized by a topological invariant (the Chern number), and the associated dissipationless conducting edge states. This implies that the IQHE can also occur in an insulating magnetic material with a nonzero Chern number (Chern insulator) without applied magnetic field. Due to its fascinating topological properties and potential applications in designing low power electronics and spintronics, intensive theoretical and experimental studies have recently been made in search for this spontaneous IQHE (better known as quantum anomalous Hall (QAH) effect) in real materials, leading to the recent observation of the QAH effect in magnetic impurity-doped topological insulators at 30 mK. In this talk, I will demonstrate, using first-principles calculations, that high temperature spontaneous IQHE would occur in ferromagnetic superlattices of heavy transition metal perovskites and also in layered chiral antiferromagnetic oxides. Furthermore, I will explain that the QAH phases in these oxides originate from two distinctly different mechanisms, namely, the conventional one due to the presence of both the relativistic spin-orbit coupling and ferromagnetism in the perovskite superlattices and the exotic quantum topological Hall effect caused by topologically nontrivial magnetic structure in the chiral antiferromagnets.
Brief Bio:
Guang-Yu Guo is currently a Distinguished Professor of NTU Physics Dept and also a National Chair Professor of the Ministry of Education. He received his PhD from Cambridge University in 1987. He joined the NTU Physics Faculty in 1998 after working in Daresbury Laboratory, UK for 11 years as a postdoc, higher and senior staff scientist. He also worked in National Chengchi University as a chair professor and the founding director of the Graduate Institute of Applied Physics during 2009-2013. He has been fruitfully conducting research in condensed matter and materials physics in the past 29 years, publishing over 200 journal papers with over 5000 citations and h-index of around 40. He has won several academic awards and honors including the National Science Council Outstanding Research Awards (1998, 2004, 2009) and the Ministry of Education 57th Academic Award (2013) and 19th National Chair Professorship (2015). He is an elected Fellow of PSROC (2005), APS (2005) and Institute of Physics (UK) (2013).