报 告 人：黄荣俊 教授
Dr. Jung-Chun A. Huang received his B.S. degree in Physics Department of National Taiwan University in 1985 and PhD degree from University of Illinois in Urbana Champaign (UIUC) in 1992. He got his associated professorship and professorship in National Cheng Kung University (NCKU, 成功大学) of Taiwan in 1992 and 1997 respectively. He has been a Distinguished Professor of NCKU since 2003. He had been the President of Physics Society of Taiwan from 2010 to 2012. He is now the Vice President of Taiwan Association for Magnetic Technology. Dr. Huang authored or co-authored nearly 180 per-reviewed papers mainly in the area of thin film epitaxy and magnetism, with a recent focus on 3D and 2D topological insulators and the related advanced devices for nanoelecronic and spintronic applications.
Ultrthin bilayers (BL) of bismuth have been predicated to be two-dimensional (2D) topological insulators. Bi bilayers prepared with a bottom-up growth method typically suffer significant surface roughness due to the limit of three dimensional (3D) growth modes. Here we report a top-down approach to prepare uniform and well ordered Bi(111) BL with deliberate hydrogen etching on epitaxial Bi2Se3 films. With a scanning tunneling microscopy (STM) in-situ, we confirm that the removal of Se from the top of a quintuple layer (QL) is the key factor, leading to a uniform formation of Bi (111) BL in the van der Waals gap between the first and second QL of Bi2Se3. Calculations based density-functional theory (DFT) predict a strong hybridization between Bi bilayers and Bi2Se3 and the number of Bi hole-like bands increasing with thickness of Bi BL, in excellent agreement with the angle-resolved photoelectron spectra (ARPES) results. A large Rashba splitting with a coupling constant of ～4.5 eV．Å is attributed to the large spin-orbit coupling (SOC) and interface potential gradient between Bi (111) BL and Bi2Se3. Similar phenomenon with subtle difference has been discovered in Bi (111) BL upon etching Bi2Te3. Compared to Bi2Se3/Cu/NiFe, enhanced spin pumping effect with large spin Hall angle has been observed in Bi2Se3/Bi BL/Cu/NiFe. The selective hydrogen etching is a promising route to produce a uniform ultrathin 2D TI that is useful for fundamental investigations and applications in spintronics.