Novel Quantum Phenomena in 2D Helium with Aspects of Quantum Phase Transition

2023 Fiscal Year Final Research Report

• Project/Area Number: 20H00132
• Research Category: Grant-in-Aid for Scientific Research (A)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Medium-sized Section 13:Condensed matter physics and related fields
• Research Institution: Keio University
• Principal Investigator: Shirahama Keiya 慶應義塾大学, 理工学部(矢上), 教授 (70251486)
• Co-Investigator(Kenkyū-buntansha): 永合 祐輔 慶應義塾大学, 理工学部(矢上), 助教 (50623435)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 物性物理 / 低温物理 / 量子流体固体 / 超流動 / 量子相転移 / ヘリウム / 非平衡

Outline of Final Research Achievements

Thin He films on solid surfaces are 2D strongly correlated systems which show a variety of novel physical phenomena. We have revealed that the properties of the He films can be understood by a physical picture, Quantum Phase Transition between a localised solid with a gap in the excitation and a (super)fluid phase with a vanishing gap. This picture is utilised to explore and elucidate novel quantum phenomena. Experiments have been carried out in searches for (1) non-equilibrium superfluidity by phonon irradiation, (2) purely 2D 3He superfluids, and (3) possible supersolid states. While (1) and (2) are still under study, in (3) we have found that He films show anomalous dielectric behaviour. It will opens a new avenue to understanding quantum phase transitions and controlling noneequilibrium properties by an external field.

Free Research Field

低温物理学

Academic Significance and Societal Importance of the Research Achievements

本研究の学術的背景は、近年の物性物理学の方向性と代表者が進めてきたヘリウム研究の整合性に基づいている。近年、トポロジーに基づく物理学が爆発的に進展しており、これまで一電子描像に留まってきたトポロジカル物質研究が、固体中電子の強相関性を取り込んでさらに発展する可能性がある。また熱平衡下では実現困難な新しい状態を非平衡下で実現する試みも、高温超伝導が観測されるなど新しい段階に入ってきた。2次元ヘリウムはこれらの概念を全て含み、トポロジカル超流動、量子液晶、外場非平衡などの新現象・新概念を示す研究対象となる。本研究は、次世代物性物理の発展に本質的寄与をなすと確信する。