Two-dimensional electronic states localized at van der Waals interfaces of layered compound ultrathin films and its electrical conduction

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03432
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13020:Semiconductors, optical properties of condensed matter and atomic physics-related
• Research Institution: Kyoto University
• Principal Investigator: Hatta Shinichiro 京都大学, 理学研究科, 助教 (70420396)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 原子層科学 / 表面科学 / 分子線エピタキシー / ヘテロ構造

Outline of Final Research Achievements

We conducted experimental research focusing on two-dimensional (2D) electronic states at van der Waals (vdW) interfaces of layered compounds, mainly by using molecular beam epitaxy, angle-resolved photoelectron spectroscopy (ARPES). We fabricated bismuth telluride (Bi2Te3) and bismuth selenide (Bi2Se3) ultrathin films with single- and few-layer thickness on calcium fluoride (CaF2) and Bi-covered Si(111) substrates. The Bi2Te3 films was found to be free-from twin structure on CaF2 and showed metallic transport due to bulk-like conduction bands whose number is in proportion to the number of vdW interfaces. We also studied iron bromide (FeBr2) thin films, which is a layered magnetic material, on a Bi(111)/Si(111) substrate. The ARPES results showed that FeBr2 remains insulating even when the film thickness decreased to a single layer. In addition, we investigated ultrathin metallic films of indium with 2D free-electron-like states.

Free Research Field

表面科学

Academic Significance and Societal Importance of the Research Achievements

固体を極めて薄くしたとき、量子効果によってその物性が大きく変化する。その極端な例がグラフェンであり、他の層状化合物においても近年次々に新しい物性の発見が続いており、それらを応用した電子デバイス等の高性能化や技術革新が期待されている。本研究では、半導体や誘電体、トポロジカル絶縁体など、異なる性質を持つ物質のヘテロ構造薄膜が作製できることと、その電子構造を解明した。これらの成果は、層状化合物薄膜の物性についての理解を深めるだけでなく、大面積での精密な構築が可能であることを示しており、今後の応用技術の発展にも寄与するものと考えられる。