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2019 Fiscal Year Final Research Report

Novel Elastic Effect and Possible Supersolidity in Helium Films

Research Project

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Project/Area Number 17H02925
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section一般
Research Field Condensed matter physics II
Research InstitutionKeio University

Principal Investigator

Shirahama Keiya  慶應義塾大学, 理工学部(矢上), 教授 (70251486)

Project Period (FY) 2017-04-01 – 2020-03-31
Keywords物性物理 / 低温物性 / ヘリウム / 超流動 / 弾性 / 量子相転移 / グラファイト / 窒化ホウ素
Outline of Final Research Achievements

We discovered "elastic anomaly" (increase in shear modulus at low temperatures) in 4He films adsorbed on graphite (Gr), a two-dimensional quantum many-body system. We also observed a coexistence of superfluidity and rigidity in the second layer. Our results shows that He films on Gr are characterized by "quantum phase transition picture", in which a insulator - superfluid transition occurs by the gap closure of localized and spatially extended states. We have studied elasticity and superfluidity of 4He films on the hexagonal boron nitride (hBN) surface, and have found elastic anomalies and superfluid transitions both of which are qualitatively same as those of the films on Gr.

Free Research Field

低温物理学

Academic Significance and Societal Importance of the Research Achievements

グラファイト(Gr)上ヘリウム(He)薄膜は最も古くから知られる2次元系であるが、近年の2次元系研究潮流の中で改めて注目されている。特に超流動固体や量子スピン液体などの新奇量子相の発現が期待される。本研究は弾性測定によりHe薄膜のエネルギー構造を解明するというユニークなアプローチで、局在状態と拡がった状態間の量子相転移描像が他のHe薄膜同様に成り立つことを明らかにした。また超流動性と剛性の共存を示唆する結果を得ており、超流動固体や量子液晶の新しい例として学術的重要性は高い。さらに六方晶窒化ホウ素表面上He薄膜の実験を初めて行い、新しい2次元量子多体系を開拓しつつある。

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Published: 2021-02-19  

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