Scanning tunneling microscope (STM) is a powerful tool in studying atomic-scale nanomagnets and quantum materials by imaging, atom manipulation and performing local spectroscopy. In the first part of my talk, I will talk about exploring single-atom or few-atom quantum magnets with low-temperature and high magnetic field STM (1, 2). By combining all-electronic pump-probe technique with low-temperature STM, we measure spin dynamics of artificially constructed quantum magnets down to nanosecond time resolution. We find their spin dynamics can be fully controlled by tuning the atomic exchange coupling with the magnetic STM tip (2). Furthermore, I will show that the atomic quantum magnets can be used as spin sensors to remotely sense the magnetic states of nearby nano-antiferromagnets (3).
In the second part of my talk, I will talk about using low-temperature STM to study the charge density wave (CDW) and superconducting materials. We focus on the 1T-structured transition metal dichalcogenides, 1T-TiSe2 and the 1T-Cu0.08TiSe2. In pristine 1T-TiSe2 we observe a long-range coherent commensurate CDW (C-CDW) order. In contrast, Cu0.08TiSe2 displays an incommensurate CDW (I-CDW) phase with localized C-CDW domains separated by domain walls. Fourier transform scanning tunneling spectroscopy studies suggest that the dominant mechanism for CDW formation in the I-CDW phase may be electron-phonon coupling (4).
(1) S. Yan et al., Nature Nano. 10, 40-45 (2015)
(2) S. Yan et al., Nano Lett. 15, 1938-1942 (2015)
(3) S. Yan et al., Science Advances (in press)
(4) S. Yan et al., Phys. Rev. Lett. 118, 106405 (2017)
Shichao Yan is now an assistant professor (Principle Investigator) in Shanghai Tech University. He received his Ph.D. in condensed matter physics from the Institute of Physics, Chinese Academy of Sciences in 2012. During his Ph.D., he visited Prof. Wilson Ho’s group in University of California, Irvine in 2008. After graduation, he joined Max Planck Institute and University of Illinois at Urbana-Champaign from 2012 to 2017 as a postdoctoral researcher. Shichao Yan's current research interest is in studying quantum materials and atomic-scale nanomagnets by using low-temperature scanning tunneling microscopy and spectroscopy. So far, he has published papers as first author or corresponding author in journals including Nature Nanotechnology, Science Advances, Physical Review Letters, Nano Letters etc.