Updated on 2022/05/26

写真a

 
TAKAYAMA, Akari
 
Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Associate Professor

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Education

  • 2008.04
    -
    2013.03

    Tohoku University   Department of Physics  

  • 2004.04
    -
    2008.03

    Fukushima University  

Degree

  • 東北大学   博士(理学)

Research Experience

  • 2018.04
    -
     

    Waseda University   Department of Physics   Assistant Professor

  • 2014.04
    -
    2018.03

    The University of Tokyo   Department of Physics   Assistant Professor

  • 2013.04
    -
    2014.03

    Tohoku University   WPI-AIMR   JSPS Research Fellowship for Young Scientists

  • 2010.04
    -
    2013.03

    Tohoku University   JSPS Research Fellowship for Young Scientists

Professional Memberships

  •  
     
     

    The Japanese Society for Synchrotron Radiation Research

  •  
     
     

    The Japan Society of Vacuum and Surface Science

  •  
     
     

    The Physical Society of Japan

 

Research Areas

  • Thin film/surface and interfacial physical properties

Research Interests

  • Surface Science

Papers

  • Scattering of topological surface-state carriers at steps on surfaces

    Naoya Fukui, Rei Hobara, Akari Takayama, Ryota Akiyama, Toru Hirahara, Shuji Hasegawa

    Physical Review B   102 ( 11 ) 115418  2020.09  [Refereed]

     View Summary

    The resistance across a step on ultrathin films of three different topological insulators, Bi2Te3, Bi2Se3, and (Bi1-xPbx)(2)Te-3, was measured through anisotropy in two-dimensional resistivity by using the in situ square fourpoint probe method in ultrahigh vacuum. The step resistance was much larger for Bi2Te3 than for Bi2Se3 in the range of 1-10 quintuple-layer thickness, due to the smaller critical thickness for isolation of topological surface states in Bi2Te3. The transmission probability of carriers across a step is much higher for the bulk-insulating (Bi1-xPbx)(2)Te-3 than bulk-metallic Bi2Te3, due to prevention of scattering of surface-state carriers into the bulk states. We were able to deduce microscopic information concerning the transmission probability at individual steps from the resistance data obtained macroscopically.

    DOI

  • Controlling of the Dirac band states of Pb-deposited graphene by using work function difference

    Y. Tsujikawa, M. Sakamoto, Y. Yokoi, M. Imamura, K. Takahashi, R. Hobara, T. Uchihashi, A. Takayama

    AIP Advances   10 ( 8 ) 085314 - 085314  2020.08  [Refereed]

    Authorship:Last author, Corresponding author

    DOI

  • Superconducting proximity effect in a Rashba-type surface state of Pb/Ge(111)

    H Huang, H Toyama, L V Bondarenko, A Y Tupchaya, D V Gruznev, A Takayama, R Hobara, R Akiyama, A V Zotov, A A Saranin, S Hasegawa

    Superconductor Science and Technology   33 ( 7 ) 075007 - 075007  2020.07  [Refereed]

    DOI

  • Two-dimensional conducting layer on the SrTiO3 surface induced by hydrogenation

    Y. Takeuchi, R. Hobara, R. Akiyama, A. Takayama, S. Ichinokura, R. Yukawa, I. Matsuda, S. Hasegawa

    Physical Review B   101 ( 8 ) 085422  2020.02  [Refereed]

    DOI

  • Structure of superconducting Ca-intercalated bilayer Graphene/SiC studied using total-reflection highenergy positron diffraction

    Y. Endo, Y. Fukaya, I. Mochizuki, A. Takayama, T. Hyodo, S. Hasegawa

    Carbon   157   857 - 862  2020.01  [Refereed]

    DOI

  • Atomic layer superconductors studied by in-situ surface electrical conductivity measurements in ultrahigh vacuum

    A. Takayama, S. Hasegawa

    Acc. Mater. Surf. Res.   ( 3 ) 87 - 96  2019.09

  • Superconducting single-atomic-layer Tl-Pb compounds on Ge(111) and Si(111) surfaces

    T. Nakamura, A. Takayama, R. Hobara, D.V. Gruznev, A.V. Zotov, A.A. Saranin, S. Hasegawa

    Applied Surface Science   479   679 - 684  2019  [Refereed]

    DOI

  • Vortex-induced quantum metallicity in the mono-unit-layer superconductor NbSe2

    Satoru Ichinokura, Yuki Nakata, Katsuaki Sugawara, Yukihiro Endo, Akari Takayama, Takashi Takahashi, Shuji Hasegawa

    Phys. Rev. B   99   220501(R)  2019  [Refereed]

    DOI

  • Alkali-metal induced band structure deformation investigated by angle-resolved photoemission spectroscopy and first-principles calculations

    S. Ito, B. Feng, M. Arita, T. Someya, W. C. Chen, A. Takayama, T. Iimori, H. Namatame, M. Taniguchi, C. M. Cheng, S. J. Tang, F. Komori, I. Matsuda

    Physical Review B   97 ( 15 ) 155423  2018.04  [Refereed]

     View Summary

    Alkali-metal adsorption on the surface of materials is widely used for in situ surface electron doping, particularly for observing unoccupied band structures by angle-resolved photoemission spectroscopy (ARPES). However, the effects of alkali-metal atoms on the resulting band structures have yet to be fully investigated, owing to difficulties in both experiments and calculations. Here, we combine ARPES measurements on cesium-adsorbed ultrathin bismuth films with first-principles calculations of the electronic charge densities and demonstrate a simple method to evaluate alkali-metal induced band deformation. We reveal that deformation of bismuth surface bands is directly correlated with vertical charge-density profiles at each electronic state of bismuth. In contrast, a change in the quantized bulk bands is well described by a conventional rigid-band-shift picture. We discuss these two aspects of the band deformation holistically, considering spatial distributions of the electronic states and cesium-bismuth hybridization, and provide a prescription for applying alkali-metal adsorption to a wide range of materials.

    DOI

  • Weak localization in bilayer graphene with Li-intercalation/desorption

    Y. Endo, S. Ichinokura, R. Akiyama, A. Takayama, K. Sugawara, K. Nomura, T. Takahashi, S. Hasegawa

    Journal of Physics: Condensed Matter   30   305701  2018  [Refereed]

    DOI

  • Unconventional Superconductivity at Si(111)-√3×√3-(Tl, Pb) One-Atom-Layer Alloy

    T. Nakamura, H. Kim, S. Ichinokura, A. Takayama, A.V. Zotov, A.A. Saranin, Y. Hasegawa, S. Hasegawa

    Phys. Rev. B   98   134505  2018  [Refereed]

    DOI

  • Thickness dependence of surface structure and superconductivity in Pb atomic layers

    H. Toyama, H. Huang, T. Nakamura, L. V. Bondarenko, A. Y. Tupchaya, D. V. Gruznev, A. Takayama, A. V. Zotov, A. A. Saranin, S. Hasegawa

    J. Phys. Soc. Japan   87   113601  2018  [Refereed]

    DOI

  • Anisotropic electronic band structure of intrinsic Si(110) studied by angle-resolved photoemission spectroscopy and first-principles calculations

    Stephane Yu Matsushita, Akari Takayama, Erina Kawamoto, Chunping Hu, Satoshi Hagiwara, Kazuyuki Watanabe, Takashi Takahashi, Shozo Suto

    PHYSICAL REVIEW B   96 ( 12 ) 125302  2017.09  [Refereed]

     View Summary

    We have studied the electronic band structure of the hydrogen-terminated Si(110)-(1 x 1) [H:Si(110)-(1 x 1)] surface using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations in the framework of density functional theory with local density approximation (LDA). The bulk-truncated H: Si(110)-(1 x 1) surface is a good template to investigate the electronic band structure of the intrinsic Si(110). In the ARPES spectra, seven bulk states and one surface state due to the H-H interaction are observed clearly. The four bulk states consisting of Si 3p(xy) orbitals exhibit anisotropic band dispersions along the high symmetric direction of (Gamma) over bar-(X) over bar and (Gamma) over bar-(X) over bar' directions, where one state shows one-dimensional character. The calculated band structures show a good agreement with the experimental results except the surface state. We discuss the exact nature of electronic band structures and the applicability of LDA. We have estimated the anisotropic effective masses of electrons and holes of Si(110) for device application.

    DOI

  • Emergence of charge density waves and a pseudogap in single-layer TiTe2

    P. Chen, Woei Wu Pai, Y. -H. Chan, A. Takayama, C. -Z. Xu, A. Karn, S. Hasegawa, M. Y. Chou, S. -K. Mo, A. -V. Fedorov, T. -C. Chiang

    NATURE COMMUNICATIONS   8   516  2017.09  [Refereed]

     View Summary

    Two-dimensional materials constitute a promising platform for developing nanoscale devices and systems. Their physical properties can be very different from those of the corresponding three-dimensional materials because of extreme quantum confinement and dimensional reduction. Here we report a study of TiTe2 from the single-layer to the bulk limit. Using angleresolved photoemission spectroscopy and scanning tunneling microscopy and spectroscopy, we observed the emergence of a (2 x 2) charge density wave order in single-layer TiTe2 with a transition temperature of 92 +/- 3 K. Also observed was a pseudogap of about 28 meV at the Fermi level at 4.2 K. Surprisingly, no charge density wave transitions were observed in two-layer and multi-layer TiTe2, despite the quasi-two-dimensional nature of the material in the bulk. The unique charge density wave phenomenon in the single layer raises intriguing questions that challenge the prevailing thinking about the mechanisms of charge density wave formation.

    DOI

  • Large-Gap Magnetic Topological Heterostructure Formed by Subsurface Incorporation of a Ferromagnetic Layer

    Toru Hirahara, Sergey V. Eremeev, Tetsuroh Shirasawa, Yuma Okuyama, Takayuki Kubo, Ryosuke Nakanishi, Ryota Akiyama, Akan Takayama, Tetsuya Hajiri, Shin-ichiro Ideta, Masaharu Matsunami, Kazuki Sumida, Koji Miyamoto, Yasumasa Takagi, Kiyohisa Tanaka, Taichi Okuda, Toshihiko Yokoyama, Shin-ichi Kimura, Shuji Hasegawa, Evgueni V. Chulkov

    NANO LETTERS   17 ( 6 ) 3493 - 3500  2017.06  [Refereed]

     View Summary

    Inducing magnetism into topological insulators is intriguing for utilizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) for technological applications. While most studies have focused on doping magnetic impurities to open a gap at the surface-state Dirac point, many undesirable effects have been reported to appear in some cases that makes it difficult to determine whether the gap opening is due to the time-reversal symmetry breaking or not. Furthermore, the realization of the QAHE has been limited to low temperatures. Here we have succeeded in generating a massive Dirac cone in a MnBi2Se4/Bi2Se3 heterostructure, which was fabricated by self-assembling a MnBi2Se4 layer on top of the Bi2Se3 surface as a result of the codeposition of Mn and Se. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the fabricated MnBi2Se4/Bi2Se3 heterostructure shows ferromagnetism up to room temperature and a clear Dirac cone gap opening of similar to 100 meV without any other significant changes in the rest of the band structure. It can be considered as a result of the direct interaction of the surface Dirac cone and the magnetic layer rather than a magnetic proximity effect. This spontaneously formed self-assembled heterostructure with a massive Dirac spectrum, characterized by a nontrivial Chern number C = -1, has a potential to realize the QAHE at significantly higher temperatures than reported up to now and can serve as a platform for developing future topotronics devices.

    DOI

  • 2 層グラフェン層間化合物の2 次元超伝導

    高橋隆, 菅原克明, 一ノ倉聖, 高山あかり, 長谷川修司

    表面科学   38 ( 9 ) 460 - 465  2017

    DOI

  • Proving Nontrivial Topology of Pure Bismuth by Quantum Confinement

    S. Ito, B. Feng, M. Arita, A. Takayama, R. -Y. Liu, T. Someya, W. -C. Chen, T. Iimori, H. Namatame, M. Taniguchi, C. -M. Cheng, S. -J. Tang, F. Komori, K. Kobayashi, T. -C. Chiang, I. Matsuda

    PHYSICAL REVIEW LETTERS   117 ( 23 ) 236402  2016.12  [Refereed]

     View Summary

    The topology of pure Bi is controversial because of its very small (similar to 10 meV) band gap. Here we perform high-resolution angle-resolved photoelectron spectroscopy measurements systematically on 14-202 bilayer Bi films. Using high-quality films, we succeed in observing quantized bulk bands with energy separations down to similar to 10 meV. Detailed analyses on the phase shift of the confined wave functions precisely determine the surface and bulk electronic structures, which unambiguously show nontrivial topology. The present results not only prove the fundamental property of Bi but also introduce a capability of the quantum-confinement approach.

    DOI

  • Superconducting Calcium-Intercalated Bilayer Graphene

    Satoru Ichinokura, Katsuaki Sugawara, Akari Takayama, Takashi Takahashi, Shuji Hasegawa

    ACS NANO   10 ( 2 ) 2761 - 2765  2016.02  [Refereed]

     View Summary

    We report the direct evidence for superconductivity in Ca-intercalated bilayer graphene C6CaC6, which is regarded as the thinnest limit of Ca-intercalated graphite. We performed the electrical transport measurements with the in situ 4-point probe method in ultrahigh vacuum under zero- or nonzero-magnetic field for pristine bilayer graphene, Li-intercalated bilayer graphene (C6LiC6) and C6CaC6 fabricated on SiC substrate. We observed that the zero-resistance state occurs in C6CaC6 with the onset temperature (T-c(onset)) of 4 K, while the T-c(onset) is gradually decreased upon applying the magnetic field. This directly proves the superconductivity origin of the zero resistance in C6CaC6. On the other hand, both pristine bilayer graphene and C6LiC6 exhibit nonsuperconducting behavior, suggesting the importance of intercalated atoms and its species to drive the superconductivity.

    DOI

  • Quantum transport properties of bilayer graphene on SiC studied by in situ four-point probe resistance measurements

    Endo Y., Ichinokura S., Suzuki K., Sugawara K., Akiyama R., Takayama A., Takahashi T., Hasegawa S.

    Meeting Abstracts of the Physical Society of Japan   71   2450 - 2450  2016

    DOI CiNii

  • In situ 電気伝導測定によるRashba 型表面構造(Tl, Pb)/Si(111)の超伝導の観測

    一ノ倉聖, 保原麗, 高山あかり, 長谷川修司, Andrey V. MATETSKIY, Leonid, V. BONDARENKO、Alexandra Y. TUPCHAYA, Dimitry V. GRUZNEV, Andrey V. ZOTOV、Alexander, A. SARANIN

    表面科学   37 ( 8 ) 363 - 368  2016

  • Two-Dimensional Superconductor with a Giant Rashba Effect: One-Atom-Layer Tl-Pb Compound on Si(111)

    A. V. Matetskiy, S. Ichinokura, L. V. Bondarenko, A. Y. Tupchaya, D. V. Gruznev, A. V. Zotov, A. A. Saranin, R. Hobara, A. Takayama, S. Hasegawa

    PHYSICAL REVIEW LETTERS   115 ( 14 ) 147003  2015.10  [Refereed]

     View Summary

    A one-atom-layer compound made of one monolayer of Tl and one-third monolayer of Pb on a Si(111) surface having root 3 x root 3 periodicity was found to exhibit a giant Rashba-type spin splitting of metallic surface-state bands together with two-dimensional superconducting transport properties. Temperature-dependent angle-resolved photoelectron spectroscopy revealed an enhanced electron-phonon coupling for one of the spin-split bands. In situ micro-four-point-probe conductivity measurements with and without magnetic field demonstrated that the (Tl, Pb)/Si(111) system transformed into the superconducting state at 2.25 K, followed by the Berezinskii-Kosterlitz-Thouless mechanism. The 2D Tl-Pb compound on Si(111) is believed to be the prototypical object for prospective studies of intriguing properties of the superconducting 2D system with lifted spin degeneracy, bearing in mind that its composition, atomic and electron band structures, and spin texture are already well established.

    DOI

  • Rashba effect of bismuth thin film on silicon studied by spin-resolved ARPES

    A. Takayama, T. Sato, S. Souma, T. Takahashi

    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA   201   105 - 109  2015.05  [Refereed]

     View Summary

    We report high-resolution spin- and angle-resolved photoemission spectroscopy of bismuth thin film on Si(1 1 1) to discuss the spin structure of surface states. We found that, unlike conventional picture of the Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric between two hole pockets across the Brillouin-zone center. In addition, these pockets exhibit a giant out-of-plane spin polarization as large as the in-plane counterpart, which changes the sign across the (Gamma) over bar (M) over bar line. We also revealed that the spin polarization of the Rashba surface states near the Brillouin-zone boundary (the (M) over bar point) is gradually reduced on decreasing the film thickness. Our result provides a new pathway to generate and control spin-polarized electrons in the Rashba system. (C) 2014 Elsevier B.V. All rights reserved.

    DOI

  • Topological proximity effect in a topological insulator hybrid

    T. Shoman, A. Takayama, T. Sato, S. Souma, T. Takahashi, T. Oguchi, Kouji Segawa, Yoichi Ando

    NATURE COMMUNICATIONS   6   6547  2015.03  [Refereed]

     View Summary

    It is well known that a topologically protected gapless state appears at an interface between a topological insulator and an ordinary insulator; however, the physics of the interface between a topological insulator and a metal has largely been left unexplored. Here we report a novel phenomenon termed topological proximity effect, which occurs between a metallic ultrathin film and a three-dimensional topological insulator. We study one bilayer of bismuth metal grown on the three-dimensional topological insulator material TlBiSe2, and by using spin-and angle-resolved photoemission spectroscopy, we found evidence that the topological Dirac-cone state migrates from the surface of TlBiSe2 to the attached one-bilayer Bi. We show that such a migration of the topological state occurs as a result of strong spin-dependent hybridization of the wave functions at the interface, which is also supported by our first-principles calculations. This discovery points to a new route to manipulating the topological properties of materials.

    DOI

  • Role of Quantum and Surface-State Effects in the Bulk Fermi Level Position of Ultrathin Bi films

    T. Hirahara, T. Shirai, A. Takayama, T. Hajiri, M. Matsunami, K. Tanaka, S. Kimura, S. Hasegawa, K. Kobayashi

    Physical Review Letters   115   106803  2015.02  [Refereed]

    DOI

  • One-Dimensional Edge States with Giant Spin Splitting in a Bismuth Thin Film

    A. Takayama, T. Sato, S. Souma, T. Oguchi, T. Takahashi

    PHYSICAL REVIEW LETTERS   114 ( 6 ) 066402  2015.02  [Refereed]

     View Summary

    To realize a one-dimensional (1D) system with strong spin-orbit coupling is a big challenge in modern physics, since the electrons in such a system are predicted to exhibit exotic properties unexpected from the 2D or 3D counterparts, while it was difficult to realize genuine physical properties inherent to the 1D system. We demonstrate the first experimental result that directly determines the purely 1D band structure by performing spin-resolved angle-resolved photoemission spectroscopy of Bi islands on a silicon surface that contains a metallic 1D edge structure with unexpectedly large Rashba-type spin-orbit coupling suggestive of the nontopological nature. We have also found a sizable out-of-plane spin polarization of the 1D edge state, consistent with our first-principles band calculations. Our result provides a new platform to realize exotic quantum phenomena at the 1D edge of the strong spin-orbit-coupling systems.

    DOI

  • 23pAS-6 Electronic structure of a topological insulator/magnetic insulator ultrathin film heterostructure

    Hirahara T., Kubo T., Mateckij Andrei, Takayama A., Matsunami M., Hajiri T., Tanaka K., Kimura S., Hasegawa S.

    Meeting Abstracts of the Physical Society of Japan   70   2630 - 2630  2015

    DOI CiNii

  • 21aCN-3 Topological proximity effect at the interface of Rashba metal and topological insulator studied by high-resolution ARPES

    Shoman T., Sato T., Takayama A., Souma S., Takahashi T., Oguchi T., Segawa K., Ando Y.

    Meeting Abstracts of the Physical Society of Japan   70   1419 - 1419  2015

    DOI CiNii

  • 21pPSB-6 Observation of circular dichroism in photovoltage by the Rashba effect of Bi and Bi/Ag thin film

    Ishihara H., Fukui N., Hanazuka M., Hobara R., Takayama A., Hirahara T., Hasegawa S.

    Meeting Abstracts of the Physical Society of Japan   70   2533 - 2533  2015

    DOI CiNii

  • 21pPSB-49 Transport property of magnetic insulator/topological insulator interface in MnSe/Bi_2Se_3 thin film

    Kubo T., Fukui N., Ichinokura S., Hobara R., Takayama A., Hasegawa S.

    Meeting Abstracts of the Physical Society of Japan   70   2575 - 2575  2015

    DOI CiNii

  • スピン分解ARPES によるBi エッジ構造の1 次元Rashba 効果の観測

    高山あかり, 佐藤宇史, 相馬清吾, 小口多美夫, 高橋隆

    表面科学   36 ( 8 ) 412 - 417  2015

  • Rashba effect in antimony and bismuth studied by spin-resolved ARPES

    A. Takayama, T. Sato, S. Souma, T. Takahashi

    NEW JOURNAL OF PHYSICS   16   055004  2014.05  [Refereed]

     View Summary

    We have performed spin- and angle-resolved photoemission spectroscopy of antimony (Sb) and bismuth (Bi) thin films grown on Si(111) to elucidate the nature of the Rashba effect in the spin-split surface bands. In Sb, we revealed spin polarization with the in-plane vortical texture on an elongated hole-like Fermi surface. The spin polarization is strongly momentum-dependent, almost vanishing at the region away from the Brillouin zone center. Such unusual suppression of the spin polarization is not observed in Bi, pointing to a strong influence from the quantized bulk bands on the surface spin polarization in Sb. The present result strongly suggests that bulk-surface interband scattering should be properly taken into account to understand the Rashba surface states in group-V semimetals.

    DOI

  • Relationship between Fermi surface warping and out-of-plane spin polarization in topological insulators: A view from spin- and angle-resolved photoemission

    M. Nomura, S. Souma, A. Takayama, T. Sato, T. Takahashi, K. Eto, Kouji Segawa, Yoichi Ando

    Physical Review B - Condensed Matter and Materials Physics   89 ( 4 )  2014.01  [Refereed]

     View Summary

    We have performed spin- and angle-resolved photoemission spectroscopy of the topological insulator Pb(Bi,Sb)2Te4 and observed significant out-of-plane spin polarization on the hexagonally warped Dirac-cone surface state. To put this into context, we carried out quantitative analysis of the warping strengths for various topological insulators [Pb(Bi,Sb)2Te4, Bi2Te3, Bi2Se3, and TlBiSe2] and elucidated that the out-of-plane spin polarization Pz is systematically correlated with the warping strength. However, the magnitude of Pz is found to be only half that expected from the k·p theory when the warping is strong. Besides confirming a universal relationship between the spin polarization and the surface state structure, our data provide an empirical guiding principle for tuning the spin polarization in topological insulators. © 2014 American Physical Society.

    DOI

  • Relationship between Fermi surface warping and out-of-plane spin polarization in topological insulators: A view from spin- and angle-resolved photoemission

    M. Nomura, S. Souma, A. Takayama, T. Sato, T. Takahashi, K. Eto, Kouji Segawa, Yoichi Ando

    PHYSICAL REVIEW B   89 ( 4 ) 045134  2014.01  [Refereed]

     View Summary

    We have performed spin- and angle-resolved photoemission spectroscopy of the topological insulator Pb(Bi,Sb)(2)Te-4 and observed significant out-of-plane spin polarization on the hexagonally warped Dirac-cone surface state. To put this into context, we carried out quantitative analysis of the warping strengths for various topological insulators [Pb(Bi,Sb)(2)Te-4, Bi2Te3, Bi2Se3, and TlBiSe2] and elucidated that the out-of-plane spin polarization P-z is systematically correlated with the warping strength. However, the magnitude of P-z is found to be only half that expected from the k . p theory when the warping is strong. Besides confirming a universal relationship between the spin polarization and the surface state structure, our data provide an empirical guiding principle for tuning the spin polarization in topological insulators.

    DOI

  • Spin Polarization of Gapped Dirac Surface States Near the Topological Phase Transition in TlBi(S1-xSex)(2)

    S. Souma, M. Komatsu, M. Nomura, T. Sato, A. Takayama, T. Takahashi, K. Eto, Kouji Segawa, Yoichi Ando

    PHYSICAL REVIEW LETTERS   109 ( 18 ) 186804  2012.11  [Refereed]

     View Summary

    We performed systematic spin- and angle-resolved photoemission spectroscopy of TlBi(S1-xSex)(2) which undergoes a topological phase transition at x similar to 0.5. In TlBiSe2 (x = 1.0), we revealed a helical spin texture of Dirac-cone surface states with an intrinsic in-plane spin polarization of similar to 0.8. The spin polarization still survives in the gapped surface states at x > 0: 5, although it gradually weakens upon approaching x = 0.5 and vanishes in the nontopological phase. No evidence for the out-of-plane spin polarization was found, irrespective of x and momentum. The present results unambiguously indicate the topological origin of the gapped Dirac surface states, and also impose a constraint on models to explain the origin of mass acquisition of Dirac fermions.

    DOI

  • Anomalous Rashba effect of bismuth(111) thin films studied by high-resolution spin- and angle-resolved photoemission spectroscopy

    Akari Takayama, Takafumi Sato, Seigo Souma, Takashi Takahashi

    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B   30 ( 4 ) 04E107  2012.07  [Refereed]

     View Summary

    The authors have developed an ultrahigh-resolution spin-resolved photoemission spectrometer equipped with a highly efficient mini Mott detector and a high-intensity xenon plasma discharge lamp. An electron deflector situated between the hemispherical electron-energy analyzer and the Mott detector enables the determination of the electron's spin-polarization in three independent directions and the spectrometer achieves an energy resolution of 0.9 and 8 meV for nonspin-resolved and spin-resolved modes, respectively. By using this spectrometer, we have performed spin-and angle-resolved photoemission spectroscopy of bismuth thin films on Si(111) to investigate the spin structure of surface states. Unlike conventional Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric across the zone center between the two elongated surface hole pockets and there is a giant out-of-plane spin polarization. The authors discuss these unusual spin textures in terms of a possible time-reversal symmetry breaking. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4731467]

    DOI

  • Tunable Spin Polarization in Bismuth Ultrathin Film on Si(111)

    Akari Takayama, Takafumi Sato, Seigo Souma, Tamio Oguchi, Takashi Takahashi

    NANO LETTERS   12 ( 4 ) 1776 - 1779  2012.04  [Refereed]

     View Summary

    We performed a spin- and angle-resolved photoemission spectroscopy of bismuth ultrathin film on Si(111) with various film thickness d. We found that the spin polarization of spin-split Rashba surface states near the Brillouin-zone boundary, which is high (0.7) at d = 40 BL (bilayers), is gradually reduced on decreasing d and almost vanishes at d = 8 BL. This finding provides a novel method to generate spin-polarized electrons with tunable spin-polarization.

    DOI

  • Anomalous Rashba effect of bismuth(111) thin films studied by high-resolution spin- and angle-resolved photoemission spectroscopy

    Akari Takayama, Takafumi Sato, Seigo Souma, Takashi Takahashi

    Journal of Vacuum Science and Technology B:Nanotechnology and Microelectronics   30 ( 4 )  2012  [Refereed]

     View Summary

    The authors have developed an ultrahigh-resolution spin-resolved photoemission spectrometer equipped with a highly efficient mini Mott detector and a high-intensity xenon plasma discharge lamp. An electron deflector situated between the hemispherical electron-energy analyzer and the Mott detector enables the determination of the electron's spin-polarization in three independent directions and the spectrometer achieves an energy resolution of 0.9 and 8 meV for nonspin-resolved and spin-resolved modes, respectively. By using this spectrometer, we have performed spin- and angle-resolved photoemission spectroscopy of bismuth thin films on Si(111) to investigate the spin structure of surface states. Unlike conventional Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric across the zone center between the two elongated surface hole pockets and there is a giant out-of-plane spin polarization. The authors discuss these unusual spin textures in terms of a possible time-reversal symmetry breaking. © 2012 American Vacuum Society.

    DOI

  • 高分解能スピン分解光電子分光装置の開発と表面ラシュバ効果の研究

    高山あかり, 相馬清吾, 高橋隆

    表面科学   33 ( 3 ) 165 - 171  2012

  • Evolution of surface states in Bi1-xSbx alloys across the topological phase transition

    H. Guo, K. Sugawara, A. Takayama, S. Souma, T. Sato, N. Satoh, A. Ohnishi, M. Kitaura, M. Sasaki, Q. -K. Xue, T. Takahashi

    PHYSICAL REVIEW B   83 ( 20 ) 201104(R)  2011.05  [Refereed]

     View Summary

    We performed a systematic, high-resolution, angle-resolved photoemission spectroscopy of Bi1-x Sb-x alloys to study the evolution of electronic states as a function of Sb concentration x. We revealed that the number of Fermi-level crossings is different between the topologically trivial (x = 0.023) and nontrivial (x = 0.17) phases: four and five times for the former and latter cases, respectively. We also found a systematic expansion of the bandwidth of spin-split surface bands at the (Gamma) over bar point upon substituting Bi with Sb, which is indicative of the monotonous reduction of the spin-orbit coupling strength.

    DOI

  • Direct Measurement of the Out-of-Plane Spin Texture in the Dirac-Cone Surface State of a Topological Insulator

    S. Souma, K. Kosaka, T. Sato, M. Komatsu, A. Takayama, T. Takahashi, M. Kriener, Kouji Segawa, Yoichi Ando

    PHYSICAL REVIEW LETTERS   106 ( 21 ) 216803  2011.05  [Refereed]

     View Summary

    We have performed spin-and angle-resolved photoemission spectroscopy of Bi2Te3 and present the first direct evidence for the existence of the out-of-plane spin component on the surface state of a topological insulator. We found that the magnitude of the out-of-plane spin polarization on a hexagonally deformed Fermi surface of Bi2Te3 reaches maximally 25% of the in-plane counterpart, while such a sizable out-of-plane spin component does not exist in the more circular Fermi surface of TlBiSe2, indicating that the hexagonal deformation of the Fermi surface is responsible for the deviation from the ideal helical spin texture. The observed out-of-plane polarization is much smaller than that expected from the existing theory, suggesting that an additional ingredient is necessary for correctly understanding the surface spin polarization in Bi2Te3.

    DOI

  • Giant Out-of-Plane Spin Component and the Asymmetry of Spin Polarization in Surface Rashba States of Bismuth Thin Film

    A. Takayama, T. Sato, S. Souma, T. Takahashi

    PHYSICAL REVIEW LETTERS   106 ( 16 ) 166401  2011.04  [Refereed]

     View Summary

    We have performed high-resolution spin-and angle-resolved photoemission spectroscopy of bismuth thin film on Si(111) to investigate the spin structure of surface states. Unlike the conventional Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric between the two elongated surface hole pockets across the zone center. Moreover, we uncovered a giant out-of-plane spin polarization as large as the in-plane counterpart which switches the sign across the (Gamma) over bar-(M) over bar line. We discuss the present finding in terms of the symmetry breaking and the many-body effects.

    DOI

  • Erratum: Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector [Review of Scientific Instruments (2010) 81 (095101))

    S. Souma, A. Takayama, K. Sugawara, T. Sato, T. Takahashi

    Review of Scientific Instruments   81 ( 10 )  2010.10  [Refereed]

    DOI

  • Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector

    S. Souma, A. Takayama, K. Sugawara, T. Sato, T. Takahashi

    REVIEW OF SCIENTIFIC INSTRUMENTS   81 ( 9 ) 095101  2010.09  [Refereed]

     View Summary

    We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90 degrees electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3480542]

    DOI

  • Magnetic Phase Transition of CeSb Studied by Low-Energy Angle-Resolved Photoemission Spectroscopy

    Akari Takayama, Seigo Souma, Takafumi Sato, Toshiyuki Arakane, Takashi Takahashi

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   78 ( 7 ) 073702  2009.07  [Refereed]

     View Summary

    We have performed low-energy ultrahigh-resolution angle-resolved photoemission spectroscopy on CeSb to elucidate the bulk electronic structure responsible for the magnetic phase transition. By using a newly developed xenon-plasma discharge lamp, we clearly observed the splitting of Sb 5p(3/2) and Cc 5d bands near the Fermi level as well as their strong hybridization below the Neel temperature (T-N = 16 K). We also revealed distinct differences in the band structure between the antiferropara- and antiferromagnetic phases. These experimental results are discussed in terms of the p-f/p-d mixing effect, the exchange splitting, and the magnetic band-folding. The present result also explains the emergence of fine structures in the optical conductivity in the magnetic phase.

    DOI

  • Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba(0.6)K(0.4)Fe(2)As(2)

    H. Ding, P. Richard, K. Nakayama, K. Sugawara, T. Arakane, Y. Sekiba, A. Takayama, S. Souma, T. Sato, T. Takahashi, Z. Wang, X. Dai, Z. Fang, G. F. Chen, J. L. Luo, N. L. Wang

    EPL   83 ( 4 ) 47001  2008  [Refereed]

     View Summary

    We have performed a high-resolution angle- resolved photoelectron spectroscopy study on the newly discovered superconductor Ba(0.6)K(0.4)Fe(2)As(2) (T(c) = 37 K). We have observed two superconducting gaps with different values: a large gap (Delta similar to 12 meV) on the two small hole-like and electron-like Fermi surface (FS) sheets, and a small gap (similar to 6meV) on the large hole-like FS. Both gaps, closing simultaneously at the bulk transition temperature (T(c)), are nodeless and nearly isotropic around their respective FS sheets. The isotropic pairing interactions are strongly orbital dependent, as the ratio 2 Delta/k(B)T(c) switches from weak to strong coupling on different bands. The same and surprisingly large superconducting gap due to strong pairing on the two small FSs, which are connected by the (pi, 0) spin-density-wave vector in the parent compound, strongly suggests that the pairing mechanism originates from the inter-band interactions between these two nested FS sheets. Copyright (c) EPLA, 2008.

    DOI

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Books and Other Publications

  • High-Resolution Spin-Resolved Photoemission Spectrometer and the Rashba Effect in Bismuth Thin Films (Springer Theses)

    Akari Takayama( Part: Sole author)

    Springer  2015

    ASIN

Misc

  • 10pAS-1 Topological proximity effect in Bi/TlBiSe_2 studied by high-resolution ARPES

    Shoman T., Takayama A., Sato T., Souma S., Takahashi T., Oguchi T., Segawa K., Ando Y.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 ) 677 - 677  2014.08

    CiNii

  • 10pAS-1 Topological proximity effect in Bi/TlBiSe_2 studied by high-resolution ARPES

    Shoman T., Takayama A., Sato T., Souma S., Takahashi T., Oguchi T., Segawa K., Ando Y.

    Meeting abstracts of the Physical Society of Japan   69 ( 2 ) 461 - 461  2014.08

    CiNii

  • 28aBF-9 Electronic states of Bi-deposited TlBiSe2 studied by High-resolution ARPES

    Shoman T., Takayama A., Tanaka Y., Sugawara K., Souma S., Sato T., Takahashi T., Eto K., Segawa K., Ando Y.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 ) 706 - 706  2014.03

    CiNii

  • 27pAQ-3 Edge state of Bi thin film studied by spin-resolved ARPES

    Takayama A., Sato T., Souma S., Oguchi T., Takahashi T.

    Meeting abstracts of the Physical Society of Japan   69 ( 1 ) 873 - 873  2014.03

    CiNii

  • Anomalous electronic structure of Bi/Si(111) surface studied by high-resolution ARPES

    Takayama A., Sato T., Souma S., Oguchi T., Takahashi T.

    Meeting abstracts of the Physical Society of Japan   68 ( 2 ) 786 - 786  2013.08

    CiNii

  • 18pFE-6 High-resolution spin-resolved ARPES study of Sb thin film

    Takayama A., Sato T., Souma S., Takahashi T.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 ) 815 - 815  2012.08

    CiNii

  • 20aFJ-12 Spin-dependent electronic states near the quantum phase transition of a Tl-based topological insulator

    Sato T., Souma S., Komatsu M., Nomura M., Takayama A., Takahashi T., Eto K., Segawa K., Ando Y.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 ) 698 - 698  2012.08

    CiNii

  • 20aEA-9 Spin-resolved ARPES study of TlBi(S, Se)_2

    Souma S., Komatsu M., Nomura M., Sato T., Takayama A., Takahashi T., Eto K., Segawa K., Ando Y.

    Meeting abstracts of the Physical Society of Japan   67 ( 2 ) 632 - 632  2012.08

    CiNii

  • 24pCK-3 Film-thickness dependence of spin polarization of surface electronic states in Bi/Si(111) thin film

    Takayama A., Sato T., Souma S., Oguchi T., Takahashi T.

    Meeting abstracts of the Physical Society of Japan   67 ( 1 ) 939 - 939  2012.03

    CiNii

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Awards

  • 一般財団法人エヌエフ基金 第7回研究開発奨励賞

    2018.11   一般財団法人エヌエフ基金  

  • 日本応用物理学会「薄膜・表面物理分科会 論文賞」

    2018.03  

    Winner: 一ノ倉 聖, 菅原 克明, 高山 あかり, 高橋 隆, 長谷川修司

  • 日本物理学会 日本物理学会若手奨励賞(領域9)

    2015.03  

  • 井上科学振興財団 第7回井上リサーチアウォード

    2014.12  

  • 日本表面科学会 講演奨励賞(新進研究者部門)

    2014.05  

  • 日本ロレアル ロレアル-ユネスコ女性科学者 日本奨励賞

    2013.09  

  • 東北大学青葉理学振興会 青葉理学振興会賞

    2013.03  

  • 東北大学 総長優秀学生賞

    2013.03  

  • 東北大学 総長賞

    2013.03  

  • 日本学術振興会 第3回育志賞

    2013.03  

  • 東北大学青葉理学振興会 黒田チカ賞

    2012.03  

  • 東北大学 物理学専攻賞

    2010.03  

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Research Projects

  • 陽電子と光子を用いた量子ビーム協奏利用によるディラック電子系ボロフェンの研究

    Project Year :

    2019.04
    -
    2022.03
     

     View Summary

    申単元素(ホウ素)単原子層「ボロフェン」の構造を精密に決定し,その新奇ディラック物性の起源を明らかにする.さらに新たな量子物性が期待されるボロフェンを合成するとともに,それぞれの原子構造と電子状態を系統的に明らかにする.本研究では陽電子回折法で原子構造を決定し,軟X線光電子分光で詳細に電子状態を調べる.光子(軟X線)と陽電子の2種類の量子ビームの協奏的利用による多種多様なボロフェンの系統研究により「低次元ホウ素材料科学」を新たな学問分野として切り拓くことを目的とする

  • 原子層半導体薄膜における歪みダイナミクス測定の新手法開発

    東芝メモリ  東芝メモリFS研究

    Project Year :

    2018.09
    -
    2020.03
     

  • Spin-texture mapping in k-space by spin-resolved AREPS

    Project Year :

    2014.04
    -
    2018.03
     

     View Summary

    Spin-orbit coupling (SOC) in matter strongly affects an electron’s spin which points to various directions depending on the type of SOC interaction and crystal symmetry. In this study, we have developed our spin-resolved photoemission spectrometer and, by using this, studied the electronic structure of high functional materials in which a relation between spin and momentum plays an important role in this functionality. Consequently, we have observed various intriguing electronic states; Surface Fermi arc in Weyl semimetals, As 4p hole-band in dilute magnetic semiconductor GaMnAs, one dimensional edge state in heavy metal film, unexpected surface state in line node semimetals, and so on. Based on the above results, we conclude that this project has succeeded in establishing of new topological materials and unraveling of mechanism of ferromagnetism in GaMnAs

  • 独立駆動4探針・磁性探針STMによるスピン偏極した1次元電子系の研究

    日本学術振興会  科学研究費助成事業

    Project Year :

    2015.04
    -
    2018.03
     

  • Study of Electron/Spin Transport at Molecules by Functionalized Four-Tip STM

    Project Year :

    2013.06
    -
    2018.03
     

     View Summary

    By using our four-tip scanning tunneling microscope prober with functionalized tips, we have measured charge and spin transport properties of various molecular objects and surfaces of electrodes which are components necessary for "molecular architechtonics" . (1) The conductivity of Nickel dithiolene nanosheets is very high and changes with redox control. (2) Bilayer graphene becomes superconducting around 2 K by Calcium intercalation. (3) The Berry phase of bilayer graphene changes from 0 to π by Li-intercalation and thermal desorption treatment. (4) A probe for pure spin injection has been developed

  • 多探針STM を用いた1次元Rashba 効果およびトポロジカルエッジ状態の研究

    井上科学振興財団  井上リサーチアウォード

    Project Year :

    2015.04
    -
    2017.03
     

  • Studies on Electronic and Spin Transport at Topological Surfaces and Edge States

    Project Year :

    2013.04
    -
    2016.03
     

     View Summary

    The present research on transport phenomena at surfaces of strong spin-orbit coupling materials has provided the following results. (1) Direct detection of suppression of back scattering of surface-state carriers on topological insulators. (2) Detection of photogalvanic effect (spin-polarized current induced by irradiation of circularly polarized light) at Rashba-type spin-split surface states. (3) Detection of energy-gap opening in a topological Dirac-cone type state by proximity effect of magnetic material. (4) Detection of spin Hall effect at ultrathin films of topological insulators. (5) Discovery of superconductivity at Rashba-type spin-split surface states. (6) Discovery of superconductivity at Ca-intercalated double-layer graphene

  • 高分解能スピン分解光電子分光による金属超薄膜の電子状態の研究

    日本学術振興会  科学研究費補助金

    Project Year :

    2013.04
    -
    2014.03
     

  • スピン分解超高分解能光電子分光装置の建設と磁性表面薄膜の研究

    日本学術振興会  科学研究費補助金

    Project Year :

    2010.04
    -
    2013.03
     

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Presentations

  • 角度分解光電子分光とその場伝導測定で探る 表面原子層の超伝導

    高山あかり  [Invited]

    日本物理学会2019年秋季学会 

    Presentation date: 2019.09

  • Structural analysis of bilayer-graphene intercalation compounds on SiC substrate by total-reflection high-energy positron diffraction

    Akari Takayama  [Invited]

    Presentation date: 2019.03

  • Exotic phenomena caused by spin-orbit coupling

    A. Takayama  [Invited]

    60 years of Physical Review Letters, APS/JPS Joint Symposium, JPS autumn meeting 2018  JPS

    Presentation date: 2018.09

  • 高速化データ駆動科学への期待:陽電子回折を中心に

    高山あかり  [Invited]

    ポスト「京」重点課題7研究会「データ駆動科学と高速計算科学」 

    Presentation date: 2018.07

  • Rashba 系表面超構造の超伝導

    高山あかり  [Invited]

    日本表面科学会 2017年真空・表面科学合同講演会  (横浜) 

    Presentation date: 2017.08

  • スピン分解光電子分光によるV族半金属薄膜におけるラシュバ効果の研究

    高山あかり  [Invited]

    日本物理学会第70回年次大会(領域9若手奨励賞受賞講演) 

    Presentation date: 2015.03

  • 五感で感じる電子の世界

    高山あかり  [Invited]

    第3回世界トップレベル研究拠点合同シンポジウムサイエンストークライブ 

    Presentation date: 2013.12

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Specific Research

  • 対称性の破れた原子層構造における非従来型超伝導現象の直接観測

    2021  

     View Summary

    本研究では、対称性の破れた原子層構造における非従来型超伝導現象、すなわちRashba型表面超伝導の電子状態および超伝導特性について知見を得ることを目的として理化学研究所創発物性計測研究チームと共同で研究を行った。 (Tl, Pb)/Si(111)表面超構造について極低温・強磁場下での走査トンネル電子顕微鏡/分光(STM/STS)測定を行った結果、STM観測からは以前の報告と全く違いがないにもかかわらず、STS測定では従来型の超伝導特性を示すことが明らかとなった。これらの結果は、フェルミ準位がわずかに異なることでフェルミ面の形状が変化し物性が変化するリフシッツ転位によるものだと結論付けた。

  • グラフェンのディラック電子系における超伝導ギャップの直接観測

    2020  

     View Summary

    本研究において超伝導ギャップ測定を行う予定であった実験施設への立ち入りが制限されたため、本実験予定を変更し、ディラック電子系の一種であるディラックノーダルライン型電子状態を持ち、かつ超伝導発現が理論的に示唆されている単原子層Cu2Siの電子状態および超伝導発現の有無について研究を行った。極低温・磁場下での電気伝導測定および解析の結果、弱半局在効果を観測した。一方、理論の予測とは異なり超伝導は発現しなかったが、このことはSi基板の効果による歪みが超伝導発現を阻害した可能性を示唆している。さらに、電子状態測定実験と比較した結果、この弱半局在効果はディラック電子系由来のものであると考えられる。

  • ランダム欠陥を取り入れた超巨大構造としての二次元物質解析

    2019   星健夫, 辻川夕貴

     View Summary

    本研究では⽋陥を持つグラフェンの正確な物性理解と評価のため,以下の研究を行った。(i)⽋陥を含むグラフェンの作成:脱離法によりSiC基板上に作成したグラフェンを初期構造とし、Arスパッタリングによる物理的破壊によりグラフェンへ欠損を導入した。(ii)物性測定:Arスパッタリングの印加電圧依存性(0, 0.2, 1.0 kV)をSTMおよび電気伝導測定を用いて調べた。STM測定の結果、グラフェンのテラスの概形は1.0 kVでのスパッタリング後も観測された。また、電気伝導測定の結果、0.2 kVでのスパッタリングではグラフェンの電気抵抗値の変化は少なく、1.0 kVでグラフェンからの伝導度がなくなることがわかった。今後、この試料について構造解析を行う予定である。

  • 合金系表面超構造における2次元超伝導体の探索

    2019   辻川夕貴

     View Summary

     本研究は、表面超構造における低次元超伝導の物性解明を目指す研究の基盤を形成するため、新たな2次元超構造を探索することを目的して研究を行った。ディラック電子をもつ炭素の二次元シートであるグラフェンにおいて、超伝導体であるPbを数原子層蒸着するとグラフェン上にアイランドが成長するが、STMおよび電気伝導測定の結果、Pbアイランドどうしが直接接触していなくても試料全体が超伝導を示すことを見出した。このことは、Pbアイランドからの近接効果によってグラフェン上を超伝導電流が流れていることを意味しており、この系が二次元超伝導の新たな研究舞台になることを提案した。

  • 原子層薄膜における歪みダイナミクス測定の新手法開発

    2018   保原麗

     View Summary

     本研究では「柔軟性の高いシート上」の「柔軟性の高いグラフェン」を基板として薄膜を作成し、東京大学において連携研究者とともに歪み物性測定を行った。SiC基板上に作成した2層グラフェンからカプトンテープを用いてグラフェンの剥離・転写し、走査型電子顕微鏡(SEM)を用いて観察した。この試料について電気伝導測定を行い、SiC基板上の2層グラフェンの抵抗値とおおよそ同じオーダーの抵抗値を観測した。グラファイトを用いて同様の実験を行った結果、SiC基板上のグラフェンと比べて転写率は高いものの様々な層数の薄片が混在し、層数制御は難しいことが確認できた。以上の結果は学位論文(学士)として提出・受理された。

  • 機能性原子層物質における物性・構造の完全解明

    2018  

     View Summary

    本研究は、角度分解高電子分光を用いて機能性原子層構造の電子構造の決定と物性の発現メカニズムの解明を目指した実験を行った。超伝導とディラック電子系の関係性に着目し、Pbを蒸着した2層グラフェンを用いて測定した結果、Pbアイランドによる金属的なバンド分散、さらにPb蒸着によってグラフェン特有のディラック型バンド分散がフェルミ準位側にシフトする様子を観測した。またCu/Si(111)を用いた実験では、第2ブリルアンゾーン内において新たに観測したバンドがノーダルライン型バンド分散である可能性が高いと見出した。以上の結果は、以上の成果は学位論文(学士)として提出・受理された。

  • 全反射高速陽電子回折を用いたノーダルライン半金属Cu2Siの構造解析

    2018  

     View Summary

    本研究は、ノーダルライン半金属の可能性が示唆されているCu/Si(111)の構造を詳細に決定するため、全反射⾼速陽電⼦回折(TRHEPD)法による鏡⾯反射スポット強度の視射⾓依存性について実験およびシミュレーションを用いて構造解析を行った。先行研究において提案されている3種類の銅シリサイド構造について、Si基板との距離やバックリング度合いを変化させた様々な構造モデルを構築し、その理論曲線を実際の測定結果と⽐較した結果、バックリングのない構造において、Cu2SiおよびCuSi2のロッキング曲線が実験結果と⽐較的近い曲線を⽰すことを⾒出した。このことは以上の成果は学位論文(学士)として提出・受理され、4月に学会発表を予定している。

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Syllabus

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