Image-Potential State on Ir(111) Revealed by Multiphoton Photoemission

Yu-Chan Tai^1,2*, Chih-Wei Luo², Noriaki Takagi³, Hiroshi Ishida⁴, Chun-Liang Lin², Ryuichi Arafune¹

¹MANA, National Institute for Materials Science, Tsukuba, Japan
²Dept. of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
³Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
⁴College of Humanities and Sciences, Nihon University, Tokyo, Japan

* Presenter:Yu-Chan Tai, email:brianyjtai1994@gmail.com

Multiphoton photoemission provides access to unoccupied electronic states in high-work-function materials that are beyond the reach of conventional two-photon techniques. Here we report the first experimental identification of the image-potential state (IPS) on Ir(111), with a work function of 5.83 eV, using coherent five-photon photoemission spectroscopy. The IPS exhibits parabolic dispersion with an effective mass close to that of free electrons, and its energy position agrees with predictions from both first-principles and pseudo-potential models. We further find a strong sensitivity to excitation energy: reducing the photon energy from 1.57 to 1.49 eV markedly diminishes the IPS signal, which theoretical analysis attributes to the influence of d-band proximity on initial-state population and multiphoton transition probabilities [1]. These results demonstrate the capability of multiphoton photoemission to probe IPSs in high-work-function metals, opening pathways for studying their ultrafast dynamics and interactions.

[1] Y. -C. Tai et al., Appl. Phys. Express 18, 062001 (2025)

Keywords: nonlinear light-matter interaction, multiphoton excitation, image-potential states, photoemission spectroscopy