加藤分子物性研究室


2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006 2015.1.29 "π-d系有機導体λ-(BETS)₂FeCl₄における特異な磁気構造が磁気トルクにもたらす影響" 杉浦　栞理氏（東邦大学　理学部　物理学科　物性物理学教室　M2） π-d系有機導体λ-(BETS)₂FeCl₄は、低温ゼロ磁場では反強磁性絶縁体(AFI)相を基底状態として持つが、磁場の印加に伴い絶縁体－金属－磁場誘起超伝導転移と大きく状態を変えていくことが報告されている。近年の比熱研究から、低温のAFI相はπ電子系の反強磁性秩序であること、またそれに伴いπ電子が作る内部磁場を3dスピンが受けた物性が発現していることが示唆されている。本研究では内部磁場の影響が外部磁場に対する変化を探ることを目的とし、磁気トルクと磁気熱量の測定を行った。実験の結果、外部磁場のみでは説明できない磁気トルクを観測し、緩和法比熱測定の結果とも一致するエントロピーの磁場変化を得ることができた。 2015.1.22 "Nitrogen-Vacancy in Diamond for Nanoscale Imaging" 岩瀬　文達 Negatively charged nitrogen-vacancy (NV) color centers in diamond have a magneto-optically active property and work as a fluorescence sensor for nanotesla-scale magnetic fluctuations at room temperature. Applications to the nanotechnology in the future generation such as a single spin detection and high-resolution magnetic resonance imaging are expected. In the seminar, the recent research of the NV centers is reviewed. The preparation of the diamond sample and the experimental detail of NV center nuclear magnetic resonance are described. 2015.1.15 "Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) [PEDOT:PSS] under Secondary Doping" 川椙　義高 In the last decade, PEDOT:PSS has emerged as the most successful conducting polymer because of the "secondary doping". In addition to the conventional advantages of organic materials such as flexibility and light weight, the conductivity is now comparable to ITO. I will briefly introduce the effect of the secondary doping and recent works focusing on the thermoelectric property of PEDOT:PSS. 2015.1.8 "Three Dimensional Dirac Semimetal" 圓谷　貴夫 A three-dimensional (3D) Dirac semimetal is the 3D generation of graphene having linear band dispersion around Fermi level, which has been predicted theoretically. In contrast to graphene, the Dirac points of such semimetals does not open the band gap by the spin-orbit interaction and the crossing of the linear dispersions is protected by space group symmetry. Several candidate compounds such as Cd₃As₂ and Na₃Bi were proposed by first-principles calculations and tight-binding models. 3D Dirac cones in Cd₃As₂ were observed recently by angle-resolved photoemission spectroscopy (ARPES). In this talk, recent theoretical and experimental studies for 3D Dirac semimetals are presented. A possible way of finding 3D semimetals in molecular solids is also discussed. 2014.12.18 文献調査 2014.12.11 文献調査 2014.12.04 "Ferromagnetic Superconductors" 崔　亨波 It was believed that the ferromagnetic superconductors could not come truefor a long time, because the superconducting state could be easily bedestroyed by strong internal magnetic field. However, recent discoveries in three uranium compounds (UGe, URhGe and UCoGe) are shown clear evidences that the superconductivity is coexists with ferromagnetism. Moreover, under the high magnetic field, the URhGe sample is showed a new type of Field-induced superconductivity. In this seminar, I will introduce recent progress in the magnetic and electric properties measurements on these three compounds. 2014.11.27 "Spin Order in Multilayered Dirac Fermion Systems" 田嶋　尚也博士（東邦大学　理学部　物理学科　物性物理学教室　准教授） First bulk (multilayer) two-dimensional zero-gap state with massless Dirac particles was realized in an organic conductor α-(BEDT-TTF)₂I₃ under pressure. We have succeeded in detecting the special Landau levels and those spin-split levels in this system. The most impressive phenomenon is the QHE plateaux with the steps are essence of 2D Dirac fermion systems. Those progresses led us to the some intrinsic questions in this system. In this seminar, I will discuss the peculiar spin states at low temperatures. 2014.11.20 "ESR for Dummies（アホ?でもわかる電子スピン共鳴）" 大島　勇吾 1945年にザボイスキーが電子スピン共鳴(ESR)を観測して以来、ESRは微視的な電子状態の最も直接的なプローブ法として使われてきた。これと同時並行して、新たな手法を取り入れたESR測定も多数開発されている。本セミナーでは、ESRの基本原理や測定対象を紹介し、ブラックボックス化した近年のX バンドESR装置の仕組みを丁寧に説明しつつ、どういうふうにデータを解析するのか？どういう情報が得られるのか？を紹介していく。また従来型のESRから派生し、昨今生物系の試料などに多く使われている、新たな測定手法にも言及していきたい。 2014.11.13 "Organic Thin Films" 藤山　茂樹 Self-assembled monolayers (SAM) on gold have significant applications in sensing, electrochemistry, surface protection, and microelectronics. Since the report of sulfer-based SAMs on gold 30 years ago, no truely alternatives for these ligands have been found. Although thiol-based SAMs are stable in a ultra high vacuum in the absence of light, degradation has been observed at room temperature in air. Recent finding of a new kind of SAM, N-heterocyclic carbenes that can align on gold through C-Au bond could increase the range of applications of SAM. I will show a brief history of organic thin films and several topics of physics related to molecules on metal surfaces. 2014.10.30 "フラストレート量子スピン系におけるマルチフェロイクス" 紙屋佳知博士（理研　古崎物性理論研究室）フラストレートスピン系では、しばしば電気磁気の交差相関などのマルチフェロイクス現象が見られる。本講演では我々の最近の研究より（１）渦結晶秩序（２）スピン-1/2三量体系における摂動的電荷揺らぎの２つの話題をマルチフェロイクスと絡めて紹介する。渦結晶秩序[1]は、フラストレート量子磁性体においてmulti-Qの磁気的不安定性（マグノンのボーズ凝縮）として磁場誘起の量子臨界点近傍で理論的に予想される磁気秩序の一つで、ナノスケールの渦が周期的にならんだ磁気構造を持つ。既知のマルチフェロイクス機構によると、このような磁気構造はナノスケールの電荷分布変調を伴うことが予想され、カイラル磁性体Cu2OSeO3において近年発見されたスカーミオン結晶と似た物性が期待される。後半ではスピン-1/2の三量体からなるモット絶縁体における摂動的な電荷揺らぎ[2]を議論する。孤立三量体の基底状態はS=1/2の二重項でカイラル自由度を持ち、その擬スピンは強結合のハバードモデルにおける電荷ゆらぎの低エネルギー有効演算子である。このような三量体を単位とする格子系では、磁性と分極が絡み合った有効モデルが導かれ、平均場近似からマルチフェロイックな系であることが期待される。 2014.10.23 "Phase Diagram of the Mott Transition in EtMe₃P[Pd(dmit)₂]₂ and the bad metal state" Abdel Jawad Majed博士（理研　仁科加速器研究センター　岩崎先端中間子研究室） Although the general theory of the Mott insulators was introduced in 1949, the description of the mechanism and the definitive signature of a Mott metal-insulator transitions are still not resolved. In this seminar, I will discuss the phase diagram and the critical nature of the Mott transition in EtMe₃P[Pd(dmit)₂]₂ from measurements of the resistivity, thermoelectric power and Hall coefficient in a pressurised Helium environment. The Seebeck coefficient is of particular interest as it undergoes a drastic and systematic change in proximity to the Mott-transition. Surprisingly, the metal-insulator limit as deduces from previous resistivity measurements does not coincidence with the Seebeck coefficient. In addition to this, we will also discuss the bad metal state in this compound and its relation to the Mott transition with a new insight into this strange state from the Hall coefficient measurements. 2014.10.16 "Mottness in a Doped Organic Superconductor" 大池広志博士（理研　創発物性科学研究センター　統合物性科学研究プログラム動的創発物性研究ユニット） It is well known that half-filled systems undergo the first-order Mott transition under variation of the on-site Coulomb repulsion U relative to the bandwidth W. However, questions remain regarding the case in which the band filling deviates from a half. I will introduce the pressure study of a doped organic superconductor, κ-(ET)₄Hg_2.89Br₈, with tunable U/W. We found that maximally enhanced superconductivity and a non-Fermi liquid appear around a certain pressure where mobile carriers increase critically, suggesting a possible quantum phase transition between strongly and weakly correlated regimes. Our description extends the conventional picture of a Mott metal-insulator transition at half filling to the case of a doped Mott insulator. 2014.10.09 文献調査 2014.10.02 中間報告5　大島　勇吾、藤山　茂樹 2014.09.19 "Zero-Gap State in Organic Conductor from the Topological Aspect" 鈴村　順三博士（名古屋大学名誉教授） I examine a zero-gap state (ZGS) in alpha-type organic conductor from the topological aspect using a tight binding model with seven kinds of hopping energies. The ZGS is obtained when the conduction band and valence band touches only at a Dirac point. However the ZGS is obtained only through a fine tuning of hopping energies in addition to a condition of Dirac point. Thus a clear method to obtain the ZGS is not yet known. I examine the variation of the sign of the transfer energy with the fixed amplitude. A robust ZGS is obtained among 16 kinds of the triangular pattern with the different spectrum. On the basis of these patterns, a study of searching a new material with ZGS is discussed by showing a relation between such robust ZGS and that of the alpha-(BETDT-TTF)₂I₃. 2014.09.04 物理学会発表練習、中間報告4　佐藤　慶明、岩瀬　文達、圓谷　貴夫、川椙　義高、上田　康平 2014.07.24 平成26年度中間報告3　崔　亨波、上田　康平 2014.07.17 平成26年度中間報告2　岩瀬　文達、圓谷　貴夫 2014.07.10 文献調査 2014.07.03 平成26年度中間報告1　崔　亨波、佐藤　慶明 2014.06.26 草本哲郎博士および実習生卒研発表 "Structural and Magnetic Properties of Cu(II) and Zn(II) Complexes with an Organic Radical PyBTM as Ligands" 草本　哲郎 We prepared a pyridine-containing organic radical PyBTM that was a rare example in radicals to show luminescent properties with high photo-stability. The spin density of PyBTM was revealed to distribute on the nitrogen atom of the pyridine moiety. In this situation, non-negligible spin-spin interaction via the nitrogen atom is expected between the metal ion and PyBTM in PyBTM-ligated metal complexes. I'd like to report on the structural and magnetic properties of Cu(II) and Zn(II) complexes with PyBTM as ligands in this seminar. The ferromagnetic exchange interaction was indicated between the Cu(II) and PyBTM. "発光を示す安定メチルラジカルとその金属錯体" 服部　陽平 Stable radicals are interesting compounds because of their spin and electronic properties, however luminescent radicals are rare and they had problem in their stabilities, especially under light irradiation. We designed a new fluorescent stable organic radical (PyBTM), which is persistent under UV light irradiation. In this seminar, I will talk about molecular orbitals, luminescent properties, and stability of PyBTM. Then, I will introduce my research about metal complexes containing PyBTM ligand, in which stronger fluorescences are expected. "Proton-Electron Dual Responses of Nickelladithiolene with a Ferrocene Moiety" 田主　陽 Metalladithiolenes have various physical and chemical properties based on their unique electronic structure, and we have developed novel molecular functionalities on metalladithiolenes by introducing another functional moiety such as ferrocene into the system. While the studies on the ferrocene-bound metalladitiholenes focused mainly on their electronic structures and inter-unit interaction upon oxidation, we recently discovered that the complexes are also responsive to protonation. In this seminar, I will introduce the progress in establishing the dual responsive system, in which the molecular and electronic structures of the complexes change in response to two kinds of external stimuli, proton and electron. 2014.06.19 "電界効果を用いた新しい機能性素子" 竹延　大志博士（早稲田大学　先進理工学部　応用物理学科　竹延研究室　教授）電界効果トランジスタとは、キャパシタと伝導度測定を組み合わせた極めてシンプルな素子であり、現代の情報化社会を支える最も重要な素子である。最近では、キャパシタ構造を用いたキャリア蓄積が物質に全く乱れを与えない理想的なドーピング手法であるため、物性研究の舞台としても注目されている。本講演では、キャパシタを構成する絶縁体として固体絶縁体（SiO₂）を用いた場合と電解質（イオン液体・イオンゲル）を用いた場合に実現される様々な電子状態に関して紹介したい。まず、固体絶縁体と有機半導体を組み合わせた時には、有機半導体内に電子・正孔を同時に蓄積した疑似的なpn接合が実現可能であり、極めてユニークな発光現象を実現できる。一方、電解質を用いた場合は、電気二重層に特徴的な大きな静電容量（~ 10μ F/cm²）を活かした高密度キャリア蓄積や柔軟性・伸縮性を活かした新しい機能を持つ素子が実現できる。講演では、カーボンナノチューブや遷移金属ダイカルコゲナイド原子層との組み合わせで実現される相転移現象や量子伝導、ユニークな光電変換現象などを紹介する予定である。 2014.06.12 "Single Component Molecular Conductors" 崔　亨波 Since the discovery of a single component molecular metal [Ni(tmdt)₂], the explore of organic single component metal have attracted considerable attention in recent years. In this seminar, I will introduce all efforts on the synthesis and high pressure electrical experiments on single component molecular crystals. My recent progress in metallic and superconducting single component molecular crystals work is also included. 2014.06.05 "dc Voltages in Ferromagnet-Nonmagnet Bilayers under Ferromagnetic Resonance" 川椙　義高 Spin injection into materials using spin pumping effect has attracted much attention recently. This dynamical method is considered to be more simple and applicable to a wider range of materials, compared to the conventional method using spin-polarized electric current. Experiments on various materials such as semiconductor, graphene, and conducting polymers have been actually reported. 2014.05.29 "MRFM and NanoMRI" 岩瀬　文達 One of dreams of human beings is to see objects which are too small to be apparent. The ultimate goal is to determine a single spin in materials, which produces the magnetism. A series of innovative works by D. Rugar and his colleagues at Nanoscale Studies in IBM Research seems to be showing the way. They combined technologies of atomic force microscopy and magnetic resonance, and produced a machine called magnetic resonance force microscope (MRFM). A cantilever with a magnetic tip on the head has successfully detected the statistical polarization from a resonating spin resided near the surface of Si-substrate. Moreover, they demonstrated the 3D imaging of nanoscale protein with resolution of (4 nm)^3. MRFM, however, requires a low-temperature environment in order to enhance the spin signal. A recent development using a nitrogen vacancy (NV) spin sensor in diamond has overcome the problem and enabled the detection of 1H signals from (5 nm)^3 voxel in organic samples in ambient conditions. 2014.05.22 "熱物性測定による有機導体の研究" 鴻池　貴子博士有機導体では低次元性や強い電子間相互作用を反映して多彩な電子相が現れるが，相転移の熱力学的検証に不可欠な熱測定による実験的研究は，電気抵抗測定によるものと比較して圧倒的に少ない．また圧力に対して電子物性が敏感に変化し，圧力誘起の超伝導や磁気秩序化，グラフェン同様のディラック電子系を形成する線形分散の実現にいたるまで，圧力によってさまざまな物性制御が可能である．一方，圧力下の熱測定では圧力媒体を通した熱リークが避けられないため測定は困難であり，特に大きな結晶を得ることが難しい有機導体の分野ではほとんど報告がない．このような背景のもと，本研究では有機導体の熱測定による研究に着目し，磁気熱量効果や比熱測定技術を確立するとともに，これらを圧力下での測定に応用することでグラフェンでは測定が難しいディラック電子系の比熱や熱起電力のふるまいを実験的に明らかにした． 2014.05.15 "Local Electrostatic Imaging of Buried Electron Gas at Interface Using Scanning Single-Electron Transistor" 佐藤　慶明 Physics on low-dimensional electron systems formed at the interfaces has been actively explored over the past decades because they manifest a wide variety of remarkable phenomena such as mesoscopic quantum transport, low-dimensional superconductivity, etc. Microscopic understanding on the interfacial systems is, however, still challenging since most of scanning probe methods such as STM are hindered for the buried electron system underneath the surface. In this seminar, I introduce an experimental study on the local electrostatic structure of two-dimensional electron gas at LaAlO₃/SrTiO₃ interface by means of a new type of scanning charge detector, based on a ultraclean carbon nanotube single-electron transistors (SETs) assembled on a probing tip. 2014.05.08 "Fragment Model and Phase Competition in Molecular Multi-Orbital System X[Pd(dmit)₂]₂" 妹尾　仁嗣博士（理研　古崎物性理論研究室　専任研究員） I will discuss electronic states of beta'-type Pd(dmit)₂ salts based on an effective model within the tight-binding approach, for which fragment molecular orbitals weighted mainly on either of the two ligands are chosen as basis functions. We estimate transfer integrals for a series of countercations and discuss their systematical variation, and its relation with spin frustration in the Mott insulating state. Then effects of interaction are investigated within mean-field approximation for the on-site and intersite Coulomb repulsions together with the electron-lattice couplings. We find a competition between a magnetic Mott insulating state with intramolecular antiferromagnetic pattern and a charge-lattice coupled insulating state. These peculiar states are owing to the multi-orbital nature, characteristic of the Pd(dmit)₂ salts. 2014.05.01 文献調査 2014.04.17 平成26年度年度計画 2014.04.03 "Luminescent Organic Radicals" 草本　哲郎博士（東京大学　西原研究室　助教） Organic radicals that contain S = 1/2 (or more) spins within the molecular skeletons exhibit interesting properties, such as magnetism, conductivity, and redox properties. In material chemistry, the magnetic and conducting properties of organic radical-based molecular solids have been extensively studied, which led to the discoveries of organic superconductors and organic ferromagnets. The further functionalization, especially the addition of luminescent properties to the organic radicals, would be one promising strategy to establish unique functions based on the interplay between the magnetism-conductivity-luminescence; however, it is not easy to achieve these conditions. This is because the most organic radicals do not show luminescence. The organic radicals behave as quencher of luminogens; the luminogens become non-luminescent in the presence of organic radicals. In this seminar I’d like to introduce rare examples of luminescent organic radicals. The photophysics and electronic structures are explained. I mention the future scope of the luminescent organic radicals.