Direct observation of band structure modifications from monolayer WSe2 to Janus WSSe
Masato Sakano, Shunsuke Akatsuka, Takato Yamamoto, Tianyishan Sun, Dingkun Bi, Hiroto Ogura, Naoya Yamaguchi, Fumiyuki Ishii, Natsuki Mitsuishi, Kenji Watanabe, Takashi Taniguchi, Miho Kitamura, Koji Horiba, Kenichi Ozawa, Katsuaki Sugawara, Seigo Souma, Takafumi Sato, Yuta Seo, Satoru Masubuchi, Tomoki Machida, Toshiaki Kato, Kyoko Ishizaka
公開日: 2025/10/5
Abstract
Janus monolayer transition metal dichalcogenides (TMDs), created by post-growth substitution of the top chalcogen layer, represent a new direction for engineering 2D crystal properties. However, their rapid ambient degradation and the difficulty of obtaining large-area monolayer samples have limited the available experimental probes, leaving their detailed electronic structure near the Fermi level largely unexplored. In this work, by performing micro-focused angle-resolved photoemission spectroscopy ({\mu}-ARPES) on an identical sample transformed from monolayer WSe2 to Janus WSSe via a H2 plasma-assisted chalcogen-exchange method, we reveal the evolution of its electronic band structure. We observe ARPES signature consistent with the Rashba-type spin splitting due to broken horizontal mirror symmetry, and a significant upward shift of the highest valence band at the {\Gamma}-point by approximately 160 meV. These direct observations clarify the key electronic modifications that govern the material's properties and provide a pathway for band engineering in Janus TMDs.