Professor Kelly Luo
University of Southern California
High-sensitivity optical measurement of spin-orbit torque via Sagnac MOKE interferometry
Location: 1080 Physics Research Building
Faculty Host: Roland Kawakami
Abstract: Improving the metrology of spin-orbit torques is a critical issue, because at present different commonly-used methods often give conflicting results. In this talk, I will present our recent progress in advancing spin-orbit-torque metrology by adapting an ultrasensitive optical technique (Sagnac interferometry) originally developed for measuring time-reversal-symmetry breaking in exotic superconductors, and applying it for the first time to measuring spin-orbit torques [1,2]. First, I will introduce the concept of Sagnac interferometry with an ultrahigh Kerr sensitivity of < 5μRad/√Hz. Then, I will describe how we utilize this high sensitivity to achieve quantitative and consistent optical measurements among samples with perpendicular magnetic anisotropy and in-plane anisotropy. Our method is especially advantageous for insulating magnets for which conventional transport spin-orbit torque metrology can be disrupted by magneto-thermal artifacts. It can also be applied widely to broad classes of magnets regardless of conductivity and small net magnetization. If time allows, I will report our progress in developing Sagnac interferometry with ultrafast capability and at cryogenic and high magnetic field environment that is suitable for studying van der Waals magnets.
[1] S. Karimeddiny*, T. M. Cham, D. C. Ralph, and Y. K. Luo*, Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque. arXiv: 2109.13759 (2021)
[2] S. Karimeddiny*, T. M. J. Cham*, O. Smedley, D. C. Ralph, and Y. K. Luo*, Sagnac interferometry for high-sensitivity optical measurements of spin-orbit torque. Science Advances, DOI: 10.1126/sciadv.adi9039 (2023)
Bio: Kelly is a Gabilan Assistant Professor of Physics and Astronomy at the University of Southern California starting in 2023. She was previously a Presidential Postdoctoral Fellow and Honorary Kavli Fellow at Cornell University studying spin torque dynamics in van der Waals magnets with Dan Ralph (primary), Kin Fai Mak, and Jie Shan. She received her Ph.D. in physics at the Ohio State University studying information transduction between spintronic, photonic, and magnetic states in two-dimensional hybrid systems under the guidance of Roland Kawakami in 2019. She obtained her Bachelor of Science in Physics at the Hong Kong University of Science and Technology.
