Abstract

The increasing demands in information storage and processing have continuously fueled extensive researches in magnetic materials, leading to discoveries in altermagnetic materials, spin torques arising from orbital moments, and the interplay of magnons and excitons in 2D van der Waals (vdWs) materials.   This presentation will delve into optical characterizations of spin accumulation in RuO­₂ altermagnets, terahertz (THz) emission stemming from orbital moments, and magnetization behaviors of 2D vdWs materials.  Magneto-optical Kerr effect (MOKE) has been used to investigate the anticipated spin accumulation in RuO₂ due to momentum-dependent spin-split bands.  Nonetheless, various spurious effects can confound observations typically attributed the current-introduce spin accumulation.  We show our observed results are most likely arise from thermal effects. Laser-induced THz emission has been harnessed to study the effects arising from orbit-moment, instead of conventional contributions from spin-moment.  We will elucidate the conversion between spin- and orbit moments.  Lastly, the use of quantum sensors based on nitrogen vacancy center (NV) to characterize 2D vdWs will be discussed.

Bio

John Q. Xiao, a Fellow of American Physical Society, received his BS degree in physics from Nanjing University, China.  He received his MS and Ph.D degrees in physics from the Johns Hopkins University in 1989 and 1993, respectively.  Between 1993 and 1995, he was a post doctoral fellow at the Department of Physics and Astronomy at the Johns Hopkins University.   He joined the University of Delaware as an Assistant Professor in 1995 and he is now a Unidel professor of Physics and Astronomy.  He is also an affiliated professor at the Center of Composite Materials and Department of Electrical and Computer Engineering at the University of Delaware.  His current research interests ranges over spintronics, 2D van der Waals materials, and high frequency magnetic materials and devices.