Abstract：

　　Delafossite metals ABO2 are known for their rich properties [1] and potential for realizing directional ballistic transport. This talk focuses on the surface properties of PdCoO2 and PdCrO2. First, I will report on the STM findings from their oxide-terminated surfaces [2,3], particularly on a rarely observed short-range charge order formed on the CrO2-terminated surface of PdCrO2 that, owing to its fragility, can only be captured by imaging at extremely low-currents [3]. Our calculation results suggest that surface charge disproportionation is the underlying mechanism. As for the Pd surfaces, both exhibit clear quasiparticle interference signals in their pristine form. However, when the Pd surface of PdCrO2, which can be regarded as a 2D metal, is adsorbed with hydrogen, a tiling structure consisting of closely packed hydrogen clusters is formed. This arrangement of hydrogen also leads to strong electronic localization [4], as well as extremely long-lived vibrational modes.

[1] P. Mackenzie, The properties of ultrapure delafossite metals, Rep. Prog. Phys. 80, 032501 (2017).

[2] M. Yim, D. Chakraborti, L. C. Rhodes, S. Khim, A. P. Mackenzie, and P. Wahl, Quasiparticle interference and quantum confinement in a correlated Rashba spin-split 2D electron liquid, Sci. Adv. 7, eabd7361 (2021).

[3] M. Yim et al., Avoided metallicity in a hole-doped Mott insulator on a triangular lattice, Nat. Commun. 15, 8098 (2024).

[4] M. Yim, Y. Zheng, O. R. Armitage, D. Chakraborti, C. J. Wells, S. Khim, A. P. Mackenzie, and P. Wahl, Adsorbate-induced formation of a surface-polarity-driven nonperiodic superstructure, Commun. Mater. 6, 128 (2025)

Biosketch：

Prof. Dr. Chi Ming Yim received his PhD degree from University College London (UK) in 2012, then pursued postdoctoral research at UCL and University of St Andrews (UK). In 2020, Chi Ming joined Tsung Dao Lee Institute, Shanghai Jiao Tong University, where he leads a low temperature STM group to study the exotic phenomena in strongly correlated electron materials at the atomic length scale. Till now, Chi Ming has published 39 papers in journals including Nature Materials, Nature Communications, PNAS and PRL etc. Chi Ming’s group website: https://web.tdli.sjtu.edu.cn/cmyim