报告题目 (Title)：Atomic scale study of the surfaces of delafossite PdCoO2 and PdCrO2（铜铁矿层状氧化物材料PdCoO₂与PdCrO₂表面的原子尺度研究）

报告人 (Speaker)：Chi-Ming Yim（严智明，上海交通大学李政道研究所）

报告时间 (Time)：2025年6月20日（周五）15:00-16:30

报告地点 (Place)：校本部G601

邀请人(Inviter)：张凌峰

主办部门：量子科技研究院/太阳集团tyc539物理系

报告摘要：

Delafossite (ABO₂), renowned for its highly anisotropic transport properties and exceptionally long mean free path, has recently garnered significant attention. Its potential to enable ballistic transport in micro-devices, along with its role as a platform for studying the interplay between itinerant electrons in triangularly-coordinated A atom layers and correlated electrons in BO₂ octahedral layers [1], makes it particularly intriguing. Today, I will present our latest STM findings on two key delafossite materials: PdCoO₂ and PdCrO₂ [2,3].

First, I will discuss quasiparticle interference (QPI) data obtained from the Pd- and CoO₂-terminated surfaces of PdCoO₂. These interfaces host ferromagnetic surface states [4] and inversion symmetry breaking (ISB)-driven giant spin-split surface states [5], respectively. A detailed analysis of the QPI data will be presented.

Next, I will share our findings on the CrO₂-terminated surface of PdCrO₂, an antiferromagnetic metal. Its bulk CrO₂ layers are Mott-insulating. However, exposing a CrO₂ surface layer to vacuum triggers charge disproportionation, resulting in a glassy charge-order. Electrical pulse experiments using STM reveal the glassy nature of this order, with relaxation lifetimes extending up to thousands of seconds.

Finally, I will briefly discuss our observations of the H-covered Pd-terminated surface of PdCrO₂, which exhibits remarkably sharp inelastic features with unexpectedly long excitation lifetimes of up to tens of nanoseconds [6,7].

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

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

[4] F. Mazzola et al., Itinerant ferromagnetism of the Pd-terminated polar surface of PdCoO2, Proc. Natl. Acad. Sci. U. S. A. 115, 12956 (2018).

[5] V. Sunko et al., Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking, Nature 549, 492 (2017).

[6] C. M. Yim et al., Adsorbate-induced formation of a surface-polarity-driven non-periodic superstructure, Under review.

[7] C. M. Yim et al., Non-equilibrium Effects in Vibration Modes Pumped by Inelastic Tunneling, Under review.