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Ohara Jun

Faculty of Science　Physics　Condensed Matter PhysicsAssociate Professor

Researcher basic information

■ Degree
  • 博士(理学), 北海道大学
■ URL
researchmap URLホームページURL■ Various IDs
J-Global ID■ Research Keywords and Fields
Research Field
  • Natural Science, Semiconductors, optical properties of condensed matter and atomic physics
  • Natural Science, Magnetism, superconductivity and strongly correlated systems
■ Educational Organization

Career

■ Career
Career
  • Apr. 2025 - Present
    北海道大学理学研究院, 准教授
  • Oct. 2013 - Mar. 2025
    北海道大学理学研究院, 講師
  • Oct. 2011 - Sep. 2013
    北海道大学 理学(系)研究科(研究院), 助教
  • Apr. 2010 - Sep. 2011
    Tohoku University, 産学官連携研究員
  • May 2009 - Mar. 2010
    Yokohama National University, 特任助教

Research activity information

■ Papers
  • Breakdown of the conventional spin-wave dynamics and its double-constraint modification in the spin-1/2 triangular-prism Heisenberg antiferromagnet
    Shoji Yamamoto; Jun Ohara
    Europhysics Letters, IOP Publishing, 09 Jul. 2025, [Peer-reviewed], [International Magazine]
    Scientific journal, Abstract

    Spontaneous magnon decays in an $S=\frac{1},{2}$ Heisenberg antiferromagnet on the equilateral triangular prism are investigated in terms of modified magnon Green's functions. In one dimension, the so-called infrared divergence prevents us from calculating any---whether static or dynamic---structure factor within the conventional spin-wave theory even at zero temperature. The well-known modified spin-wave theory initiated by Takahashi completely fails to treat anharmonicities to cause transverse-to-longitudinal coupling which are quite characteristic of noncollinear antiferromagnets. We propose imposing a double-constraint condition on spin waves to solve all these difficulties and get a full view of the nonlinear spin-wave dynamics in one-dimensional frustrated noncollinear antiferromagnets. We reveal a novel instability of the single-particle spectrum in the absence of any well-defined magnetically ordered ground state.
  • Photoproduction of Loop Currents in Coronene Isomers Without Any Applied Magnetic Field
    Jun Ohara; Shoji Yamamoto
    Solids, 5, 4, 640, 650, MDPI AG, 06 Dec. 2024, [Peer-reviewed], [Lead author], [International Magazine]
    Scientific journal, Applying an extended Peierls–Hubbard model to π electrons in a coronene isomer, we investigate their ground-state properties and photoinduced dynamics with particular interest in possible loop current states. Once we switch on a static magnetic field perpendicular to the coronene disk, diamagnetic (diatropic) and paramagnetic (paratropic) loop currents appear on the rim circuit and inner hub, respectively. Besides this well-known homocentric two-loop current state, heterocentric multiloop current states can be stabilized by virtue of possible electron–lattice coupling. These multiloop current states generally have a larger diamagnetic moment than the conventional two-loop one, and hence it follows that coronene, or possibly polycyclic conjugated hydrocarbons in general, may become more aromatic than otherwise with their π electrons being coupled to phonons. When we photoirradiate a ground-state coronene isomer without applying a static magnetic field, loop currents are induced in keeping with the incident light polarization. Linearly and circularly polarized lights induce heterocentric two-loop and multiloop currents, respectively, without and together with two homocentric loop currents of the conventional type, respectively. The heterocentric two-loop currents occur in a mirror-symmetric manner, which reads as the emergence of a pair of antiparallel magnetic moments, whereas the heterocentric multiloop ones appear at random in both space and time, which reads as the emergence of disordered local magnetic moments.
  • Thermal features of Heisenberg antiferromagnets on edge- versus corner-sharing triangular-based lattices: a message from spin waves
    Shoji Yamamoto; Jun Ohara
    Journal of Physics Communications, 7, 6, 065004, 065004, IOP Publishing, 01 Jun. 2023, [Peer-reviewed], [International Magazine]
    Scientific journal, Abstract

    We propose a new scheme of modifying spin waves so as to describe the thermodynamic properties of various noncollinear antiferromagnets with particular interest in a comparison between edge- versus corner-sharing triangular-based lattices. The well-known modified spin-wave theory for collinear antiferromagnets diagonalizes a bosonic Hamiltonian subject to the constraint that the total staggered magnetization be zero. Applying this scheme to frustrated noncollinear antiferromagnets ends in a poor thermodynamics, missing the optimal ground state and breaking the local U(1) rotational symmetry. We find such a plausible double-constraint condition for spin spirals as to spontaneously go back to the traditional single-constraint condition at the onset of a collinear Néel-ordered classical ground state. We first diagonalize only the bilinear terms in Holstein-Primakoff boson operators on the order of spin magnitude S and then bring these linear spin waves into interaction in a perturbative rather than variational manner. We demonstrate specific-heat calculations in terms of thus-modified interacting spin waves on various triangular-based lattices. In zero dimension, modified-spin-wave findings in comparison with finite-temperature Lanczos calculations turn out so successful as to reproduce the monomodal and bimodal specific-heat temperature profiles of the triangular-based edge-sharing Platonic and corner-sharing Archimedean polyhedral-lattice antiferromagnets, respectively. In two dimensions, high-temperature series expansions and tensor-network-based renormalization-group calculations are still controversial especially at low temperatures, and under such circumstances, modified spin waves interestingly predict that the specific heat of the kagome-lattice antiferromagnet in the corner-sharing geometry remains having both mid-temperature broad maximum and low-temperature narrow peak in the thermodynamic limit, while the specific heat of the triangular-lattice antiferromagnet in the edge-sharing geometry retains a low-temperature sharp peak followed by a mid-temperature weak anormaly in the thermodynamic limit. By further calculating one-magnon spectral functions in terms of our newly developed double-constraint modified spin-wave theory, we reveal that not only the elaborate modification scheme but also quantum corrections, especially those caused by the O(S 0) primary self-energies, are key ingredients in the successful description of triangular-based-lattice noncollinear antiferromagnets over the whole temperature range of absolute zero to infinity.
  • Multimagnon-mediated Raman scattering in two-dimensional quasiperiodic Heisenberg antiferromagnets
    Shoji Yamamoto; Jun Ohara
    Journal of Physics: Conference Series, 2461, 1, 012012, 012012, IOP Publishing, 01 Mar. 2023, [Peer-reviewed], [International Magazine]
    Scientific journal, Abstract

    We demonstrate configuration-interaction and Green’s function approaches to the Shastry-Shraiman fourth-order magnetic Raman response of Heisenberg antiferromagnets on the two-dimensional C5v Penrose and C8v Ammann-Beenker lattices. Beyond the Loudon-Fleury second-order perturbation scheme, two more symmetry species A1 and A2 become Raman-active to break the depolarized Loudon-Fleury Raman response of E2 symmetry. The A1 and A2 modes are activated by dynamic ring exchange and chiral spin fluctuations, respectively, the former of which owes much to multimagnon scatterings in a complicated manner, while the latter of which owes much to aperiodic arrangements of different rhombuses.
  • Helical magnetic ordering studied in single-crystalline GdBe13
    Hiroyuki Hidaka; Kota Mizuuchi; Eikai Hayasaka; Tatsuya Yanagisawa; Jun Ohara; Hiroshi Amitsuka
    Physical Review B, 102, 17, 06 Nov. 2020, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Photoinduced Bidirectional Magnetism against Monodirectional Electronics in Square-Antiprismatic Octacyanometalates
    Jun Ohara; Shoji Yamamoto
    Journal of the Physical Society of Japan, 89, 9, 093706, 093706, Physical Society of Japan, 15 Sep. 2020, [Peer-reviewed], [International Magazine]
    Scientific journal
  • Photocontrollable Mixed-Valent States in Platinum-Halide Ladder Compounds
    Jun Ohara; Shoji Yamamoto
    Applied Sciences, 8, 11, 2126, 2126, MDPI AG, 02 Nov. 2018, [Peer-reviewed], [International Magazine]
    Scientific journal, Employing a two-orbital extended Peierls–Hubbard model, we demonstrate the photomanipulation of mixed-valent states in platinum-halide ladder compounds. There are two types of interchain valence arrangements, namely in-phase and out-of-phase types. The conversion of the in-phase structure to the out-of-phase structure is induced by photoirradiation, which is accelerated with increasing light intensity, while the reverse process hardly occurs. The out-of-phase arrangement is highly stabilized in the photoexcited states by the interchain electron transfer.
  • Photoinduced itinerant ferromagnetism in copper octacyanomolybdates
    Jun Ohara; Shoji Yamamoto
    Journal of Physics: Conf. Series, 868, 012013-1, 012013-8, Jul. 2017
    English, International conference proceedings
  • 21pBT-11 Modified spin-wave theory on fully frustrated antiferromanets : How to modify the conventional spin waves
    Yamamoto Shoji; Ohara Jun
    Meeting Abstracts of the Physical Society of Japan, 71, 3053, 3053, The Physical Society of Japan (JPS), 2016
    Japanese
  • 22aBC-7 Theory of magnetic Raman scattering in triangular lattice antiferromagnets
    Ohara Jun; Yamamoto Shoji
    Meeting Abstracts of the Physical Society of Japan, 71, 1294, 1294, The Physical Society of Japan (JPS), 2016
    Japanese
  • The magnetic specific heat and susceptibility of triangular-lattice Heisenberg antiferromagnets
    Ohara Jun; Yamamoto Shoji; Schmidt Burkhard
    Meeting Abstracts of the Physical Society of Japan, 71, 839, 839, The Physical Society of Japan, 2016
    Japanese,

    表題模型及び関連物質の磁気比熱、帯磁率の理論計算。有限サイズ・クラスタ、熱力学極限、その振る舞いの詳細な検討。修正スピン波理論、Lanczos対角化法。

  • Modified spin-wave theory on the kagome-lattice Heisenberg antiferromagnet
    Ohara Jun; Yamamoto Shoji
    Meeting Abstracts of the Physical Society of Japan, 71, 1014, 1014, The Physical Society of Japan, 2016
    Japanese,

    表題模型の比熱、帯磁率、動的構造因子などを修正スピン波理論を用いて計算する。磁気フラストレイト系におけるスピン波記述の問題点を明らかにし、それを克服する修正条件の改良についても議論する。

  • 16aCQ-8 Bosonic representations of the thermodynamic properties of the triangular Heisenberg antiferromagnet
    Ohara Jun; Yamamoto Shoji
    Meeting Abstracts of the Physical Society of Japan, 70, 2534, 2534, The Physical Society of Japan (JPS), 2015
    Japanese
  • 22aAH-4 Modified spin-wave theory on anisotropic triangular lattice antiferromagnets
    Ohara Jun; Yamamoto Shoji
    Meeting Abstracts of the Physical Society of Japan, 70, 1153, 1153, The Physical Society of Japan (JPS), 2015
    Japanese
  • Photomagnetism in octacyanomolybdates of the square antiprism configuration
    Jun Ohara; Shoji Yamamoto
    Molybdenum and its Compounds: Applications, Electrochemical Properties and Geological Implications, 123, 152, Nova Science Publishers, Inc., 01 Jul. 2014
    English, In book
  • Intermolecular THz Vibrations Relevant to Optically and Thermally Induced Magnetic Phase Transitions in the Strongly Correlated Organic Radical TTTA
    Taro Kawano; Ikufumi Katayama; Jun Ohara; Masaaki Ashida; Jun Takeda
    Journal of the Physical Society of Japan, 83, 1, 014713, 014713, Physical Society of Japan, 15 Jan. 2014, [Peer-reviewed], [International Magazine]
    Scientific journal
  • Phototunable Magnetism in Copper Octacyanomolybdate
    Jun Ohara; Shoji Yamamoto
    SCIENTIFIC WORLD JOURNAL, 2014, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Optical manipulation of magnetism in spin-charge-coupled correlated electron systems
    Jun Ohara; Yu Kanamori; Sumio Ishihara
    Physical Review B, 88, 8, American Physical Society (APS), 07 Aug. 2013, [Peer-reviewed], [International Magazine]
    Scientific journal
  • Symmetry argument of cyano-bridged copper-molybdenum complexes
    Jun Ohara; Shoji Yamamoto
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY, 62, 12, 1797, 1801, Jul. 2013, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Platinum-halide square-prism compounds: Novel ground states and their optical features
    Shoji Yamamoto; Jun Ohara
    Platinum: Compounds, Production and Applications, 123, 145, Nova Science Publishers, Inc., Jan. 2013, [International Magazine]
    English, In book
  • Photoinduced magnetic bound state in an itinerant correlated electron system with a spin-state degree of freedom
    Yu Kanamori; Jun Ohara; Sumio Ishihara
    Physical Review B, 86, 4, American Physical Society (APS), 30 Jul. 2012, [Peer-reviewed], [International Magazine]
    Scientific journal
  • Phase competition and photomagnetism in supramolecular assemblies based on octacyanomolybdates of square antiprism configuration
    Shoji Yamamoto; Jun Ohara
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 12, 9, 12, 2565, 2569, 2012, [Peer-reviewed], [International Magazine]
    English, International conference proceedings
  • Bottom-up realization of a porous metal–organic nanotubular assembly
    Kazuya Otsubo; Yusuke Wakabayashi; Jun Ohara; Shoji Yamamoto; Hiroyuki Matsuzaki; Hiroshi Okamoto; Kiyofumi Nitta; Tomoya Uruga; Hiroshi Kitagawa
    Nature Materials, 10, 4, 291, 295, Springer Science and Business Media LLC, Apr. 2011, [Peer-reviewed], [International Magazine]
    Scientific journal
  • Optical distinction and photoinduced phase transition between degenerate ground states of polyacene
    Shoji Yamamoto; Jun Ohara
    PHYSICA B-CONDENSED MATTER, 405, 11, S365, S368, Jun. 2010, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Ground-State Properties of a Peierls-Hubbard Triangular Prism
    Shoji Yamamoto; Jun Ohara; Masa-aki Ozaki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 79, 4, Apr. 2010, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Competing ground states of a Peierls-Hubbard nanotube
    Jun Ohara; Shoji Yamamoto
    EPL, 87, 1, Jul. 2009, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Multichanneled relaxation of halogen-bridged diplatinum chain complexes photoexcited
    Shoji Yamamoto; Jun Ohara
    Physica Status Solidi (C) Current Topics in Solid State Physics, 6, 1, 144, 148, 2009, [Peer-reviewed], [International Magazine]
    English, International conference proceedings
  • Optical observations of new halogen-bridged platinum complexes assembled within a ladder lattice
    Shoji Yamamoto; Jun Ohara
    JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 20, 367, 370, Jan. 2009, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Photoproduction of spin and charge carriers in halogen-bridged binuclear platinum chain complexes
    Shoji Yamamoto; Jun Ohara
    JOURNAL OF PHYSICS-CONDENSED MATTER, 20, 41, Oct. 2008, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Optical characterization of platinum-halide ladder compounds
    Shoji Yamamoto; Jun Ohara
    PHYSICAL REVIEW B, 76, 23, Dec. 2007, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Low-energy structure of the homometallic intertwining double-chain ferrimagnets A(3)Cu(3)(PO4)(4) (A=Ca,Sr,Pb)
    Shoji Yamamoto; Jun Ohara
    PHYSICAL REVIEW B, 76, 1, Jul. 2007, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Nonlinear lattice relaxation of photoexcited diplatinum-halide chain compounds
    Jun Ohara; Shoji Yamamoto
    Physical Review B - Condensed Matter and Materials Physics, 73, 4, 2006, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Photoinduced infrared absorption of quasi-one-dimensional halogen-bridged binuclear transition-metal complexes
    Jun Ohara; Shoji Yamamoto
    Journal of Physics and Chemistry of Solids, 66, 8-9, 1571, 1574, Aug. 2005, [Peer-reviewed], [International Magazine]
    English, International conference proceedings
  • Photoinduced absorption spectra of halogen-bridged binuclear metal complexes: Possible contrast between R4[Pt2(P 2O5H2)4X]·nH2O and Pt2(CH3CS2)4I
    Jun Ohara; Shoji Yamamoto
    Journal of the Physical Society of Japan, 74, 1, 250, 253, Jan. 2005, [Peer-reviewed], [International Magazine]
    English, Scientific journal
  • Soliton-induced optical absorption of halogen-bridged mixed-valence binuclear metal complexes
    Jun Ohara; Shoji Yamamoto
    Physical Review B - Condensed Matter and Materials Physics, 70, 11, 1, 115112, Sep. 2004, [Peer-reviewed], [International Magazine]
    English, Scientific journal
■ Other Activities and Achievements
■ Lectures, oral presentations, etc.
  • 三角柱反強磁性体の磁気Ramanスペクトル
    大原潤; 鈴木浩介; 山本昌司
    日本物理学科2017年秋季大会, 20 Sep. 2017, Japanese, Oral presentation
    [Domestic Conference]
■ Syllabus
  • 計算物理学, 2024年, 修士課程, 理学院
  • 物理学Ⅰ, 2024年, 学士課程, 全学教育
  • 電磁気学Ⅱ, 2024年, 学士課程, 理学部
  • 現代物理学特論, 2024年, 学士課程, 理学部
■ Research Themes
  • Photoinduced dynamics of quantum many-body systems: essential differences from thermally and electron-doping induced dynamics
    Grants-in-Aid for Scientific Research
    01 Apr. 2012 - 31 Mar. 2015
    JUN Ohara
    In order to obtain a new insight into photoinduced quantum dynamics, we have theoretically investigated effects of photocarrier doping in halogen-bridged platinum (PtX) complexes and copper-molybdenum (CuMo) complexes. PtX complexes show a directional photoinduced phase transition between two distinct charge-density-wave (CDW) states. We can optically purify the mixed CDW state by tuning the directionality. As for CuMo complexes, which are known as photomagnets, we have revealed all the possible electronic states and illuminated a microscopic mechanism of the photoswitchable magnetism. Furthermore we have found that the photoinduced final steady state can be regarded as a hidden state which is hardly stabilized as an equilibrium state.
    Our findings not only bring about further understanding of nonequilibrium quantum dynamics induced by photoirradiation but also stimulate experimental studies on photoinduced ultrafast dynamics.
    Japan Society for the Promotion of Science, Grant-in-Aid for Young Scientists (B), Hokkaido University, 24740192