2019   2018   2017   2016   2015   2014   2013   2012   2011   2010   2009   2008   2007   2006

2016.04.05    年度報告会2(川椙、佐藤、圓谷)  

2016.03.15    予聴会  

2016.03.08    卒業発表  上田康平

2016.03.01    年度報告会1(藤山、大島、崔)  

2016.02.23    文献紹介 (藤山、大島、佐藤、川椙)  

2016.02.16    "Cooperative Interactions between Valence Bond Formation and Inter-Site Coulomb Repulsions Specific to an Interchange of Energy Levels in the Molecular Orbitals"  山本貴博士(愛媛大学理工学研究科 固体物理化学研究室 准教授)
X[M(dmit)2]2 salts [M=Pt and Pd] exhibit the interchange of energy levels in the molecular orbitals (HOMO-LUMO inversion) owing to the tight dimerization. Nevertheless, the intrinsic role of the HOMO-LUMO inversion in the charge and spin distributions has not been studied. The accumulation of the recent experimental results revealed that the valence bond ordering and the inter-site Coulomb repulsions all cooperate in this HOMO-LUMO inversion system. Interestingly, the charge and spin distribution due to the cooperative interaction between neighboring dimers is different from that within a dimer. Interestingly, the competition between these cooperative interactions is observed in several X[M(dmit)2]2 salts. This result indicates a novel degree of freedom arising from the HOMO-LUMO inversion in the present systems. The magnitudes of the intra-dimer and inter-dimer cooperative interactions are evaluated using the frequencies of the C=C stretching modes exhibiting the electron-molecular vibrational (e-mv) interaction. The ground states of X[Pd(dmit)2]2, including the anti-ferromagnetic state, is mapped using the magnitudes of cooperative interactions defined above. From the viewpoints of these cooperative interactions, I will discuss the puzzling phenomenon that the 2D layer of the spin-liquid system, β'-Et2Me2Sb[Pd(dmit)2]2, deviates from the ideal triangular lattice whereas the 2D layers of the non-magnetic insulators, β'-Et2Me2Sb[Pd(dmit)2]2 and monoclinic-EtMe3P[Pd(dmit)2]2, are close to the ideal triangular lattice.

2016.02.09    文献紹介 (加藤先生、崔、上田、圓谷)  

2016.01.26    クラスター摂動論による異方的三角格子ハバード模型の一粒子励起スペクトルの研究  関和弘博士(理研 柚木計算物性物理研究室 基礎科学特別研究員)
電子相関により実現する絶縁体にキャリアをドープした際等、電子相関が無視できない金属で起こり得るフェルミアーク現象は、ドープされた 銅酸化物や最近ではイリジウム酸化物で観測されており、パラメタ(温度・ドーピング等)空間で隣接すると考えられる超伝導相との関係を明 らかにすることが理論としても実験としても重要な研究テーマとなっている。
遷移金属酸化物が電子状態のフィリング依存性を対象としてきた一方、有機モット絶縁体は圧力や歪みによりモット 絶縁体状態から金属状態・超伝導状態へ相転移を起こせる等の電子状態の制御性の高さを用いて、これまで主にハーフフィルドの電子状態を対 象としてきた。しかし近年、実験の進展により有機モット絶縁体へのキャリアドーピングが実現してきている。種々の物質に基づくドープされ たモット絶縁体の研究が可能となることで、その電子状態の理解をさらに進展させることが期待される。

2016.01.19    経過報告会 (川椙、上田、佐藤)  

2016.01.12    経過報告会 (加藤先生、圓谷)  

2015.12.15    経過報告会1 (藤山、大島、崔)  

2015.12.08    "TBA"  Abdel Jawad Majed

2015.12.01    文献紹介 (藤山、大島、佐藤、川椙)  

2015.11.24    文献紹介 (加藤先生、崔、上田、圓谷)  

2015.11.19    "Low-Frequency Charge Carrier Dynamics in Quasi-2D Molecular Conductors"  Prof. Jens Muller (Institute of Physics, Goethe-University Frankfurt, Germany)
Electronic noise, on the one hand, is mostly considered an unwanted nuisance and is sought to be reduced or even eliminated, since it ultimately limits the accuracy of physical measurements. On the other hand, understanding the microscopic origin of the different noise sources may help to improve the signal-to-noise ratio of measurements on semiconductors and therefore the performance of semiconductor sensors and devices.
Another point of view, however, is to consider “noise as the signal”, since the frequency-dependent fluctuations are related to the autocorrelation function of the measured quantity. Therefore, fluctuation spectroscopy is a powerful tool for studying the microscopic kinetics of charge carriers in condensed-matter systems.
In this talk, we will discuss how resistance fluctuations, in particular 1/f- and random-telegraph noise, reveal otherwise ‘hidden’ pieces of information on the low-frequency dynamics of quasi-2D organic charge-transfer salts (ET)2X. We will focus on (i) the structural, glass-like ordering of the ET molecules’ terminal ethylene groups and the possibility to predict the occurrence of such a glass transition for different crystal structures, and (ii) the critical slowing down of the fluctuations at the Mott metal-insulator transition.
In an outlook, we will mention new results on insulating materials exhibiting ferroelectric ordering or relaxor-type behavior.

2015.11.10    "Atomic Layer Deposition in Solution"  佐藤 慶明
Rapid progress of nanoscience and nanotechnology pushes the device requirements toward more complex three-dimensional nanostructures and even more sophisticated functionalities. Atomic-layer-deposition (ALD), a layer-by-layer growth technique of thin film based on ‘self-limiting’ surface chemistry, is a powerful method to meet such demands because it provides atomic-scale precision of layer thickness and composition, and, importantly, is applicable to even non-planer substrates. Nevertheless, ALD has a major limitation that it needs volatile and thermally robust precursors since the deposition process is done basically in gas phase.
In this seminar, I will introduce a newly-reported ‘solution ALD’ technique, which realizes precisely controlled oxide layer growth from various kinds of precursors under milder reaction condition, without much sacrificing the merit of gas-phase ALD. .Some other solution-based layer-by-layer growth methods will be also briefly reviewed.

2015.10.27    "比熱測定から見たπ-d系有機導体λ-(BETS)2FeCl4の磁気秩序を伴う金属-絶縁体転移"  嶋田一雄氏(東邦大学 理学部物理学科 物性物理学教室 D3)
有機導体λ-(BETS)2FeCl4はπ伝導電子と局在3d電子(スピン=5/2)からなるπ-d複合電子系を有し、零磁場では8 K程度で反強磁性秩序化を伴う金属−絶縁体転移、17 T以上の磁場のもとでは磁場誘起超伝導相が現れることが知られている。これらの相転移にはdスピンの存在が強く関わっていると考えられるが、その詳細については議論が続いている。
我々はこれまでに、約10 T以下の磁場下で見られる金属−絶縁体転移の本質的な機構を明らかにするために、磁場下やアニオン置換系での比熱測定を中心とした研究を行ってきている。

2015.10.20    "[Pd(dmit)2]塩の電子状態及び分子振動に関する理論的研究"  川上貴資博士(大阪大学大学院理学研究科 化学専攻 量子化学研究室 助教)
従来より我々は、量子化学計算を用いた物性評価を行っており、分子性結晶の磁性に関しても、各手法の特性等を詳細に吟味しながら継続的に解析を行ってきた。各種計算手法のうち、例えば、密度汎関数法(DFT)はpost-Hartree Fock(HF)法と比べ、大規模な系を計算することが可能であり、実在系にも多く適用できる。また、近年の発展がめまぐるしいDMRG-CAS法は、スピンフラストレーション系や金属錯体の解析に、非常に有効である。
(1) 計算した物性量と実験値を比較し、Pd(dmit)2の計算における種々の汎関数の信頼性を確かめる。
(2) 計算から得られる分子軌道からPd(dmit)2二量体の物性量と、電荷の揺らぎや分子間相互作用とを関係づける。
(3) 理研加藤研究室での一連のPd(dmit)2結晶に関しての系統的な計算結果を紹介する。

2015.10.13    文献紹介 (藤山、大島、佐藤、川椙)  

2015.10.06    文献紹介 (加藤先生、崔、上田、圓谷)  

2015.09.29    中間報告2 (川椙、上田、佐藤)  

2015.09.15    予聴会(物理学会9/16-19)  

2015.08.25    中間報告1 (藤山、崔、大島)  

2015.07.21    "Electronic Transport of Low Dimensional Hybrid Nanomaterials: Colloidal Quantum Dot Assemblies and Polymer-wrapped Carbon Nanotubes"  Dr. Satria Zulkarnaen Bisri (RIKEN CEMS:岩佐チーム
The exploitation of quantum-size-effect in solution-processable nanomaterials is prospective for broad range applications, including energy-harvesting- and low-energy-consumption devices that will contribute to the future sustainable development of our society. Nevertheless, many of physical properties of these materials associated with the charge transport are still not well understood in particular when translating them into solid-state assemblies. Many challenges related with the charge transport still hampering their use for high-end and high-speed applications. I will present experimental studies on the field-effect control of charge carrier transport in colloidal quantum dot assemblies (0D) and polymer-wrapped carbon nanotubes networks (1D). Through fine tuning of field-induced carrier doping utilizing field-effect transistors, ambipolar transport - coexisting of holes and electron current - are demonstrated in these materials with high mobility values. This ambipolar transport provides opportunity to investigate the dynamics of both holes and electrons in the materials system with different conditions such as very high carrier density, high electric field, as well as high current density operation. Applications of these solution-processable nanomaterials as well as both ambipolar transistor and electric-double-layer transistor techniques are promising to become rich playground for novel (opto)electronic properties and emerging sources of new device functionalities such as flexible exa-scale computing, photovoltaic and thermoelectric devices.

2015.07.14    "磁性と誘電・伝導性が相関した物質におけるマルチプローブ研究"  本田孝志博士(高エネルギー加速器研究機構 物質構造科学研究所 博士研究員)
[1] J. S. White, T. Honda et al., Phys. Rev. Lett. 108, 077204 (2012).
[2] T. Honda et al., J. Phys. Soc. Jpn. 81, 103703 (2012).
[3] Y. Togawa et al., Phys. Rev. Lett. 111, 197204 (2013).
[4] T. Honda et al., (in preparation) (2015).

2015.07.07    文献紹介 (藤山、大島、佐藤、川椙)

2015.06.30    文献紹介 (加藤先生、崔、上田、岩瀬、圓谷)

2015.06.23    経過報告会 (川椙、岩瀬、上田、佐藤)  

2015.06.16    経過報告会 (藤山、崔、大島)  

2015.06.02    "Electron Transfer through Weak-Hydrogen Bonds"  上田康平
Recently, some relatively strong interactions between C-H…O and C-H…pi have been noted, and the hydrogen-bond concept was expanded to such interactions as weak hydrogen-bond. These strengths are weaker than O-H…O and N-H…O type hydrogen bonds; however, the role of these are important in condensed matters (of course molecular conductors) because weak hydrogen-bonds are coexistent in many directions between non-special function groups. In this seminar, I will introduce the perturbation effect of such weak hydrogen bonds for molecular orbitals of proton acceptor and proton donor: for example charge transfer and MO hybridize.

2015.05.26    "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(筑波大)

2015.05.12    文献紹介(藤山、大島、佐藤、岩瀬)

2015.04.28    文献紹介(加藤先生、崔、上田、川椙、圓谷)

2015.04.21    "Mott Transition in EtMe3P[Pd(dmit)2]2"  Abdel Jawad Majed
Studies of the metal-insulator transition of the Mott type is of great interest to the condensed matter community as anomalous superconducting states are often found in proximity to such a transition. In this talk, I will summarize the current experiential results related to the Mott transition and present the pressure and temperature dependence of the Hall coefficient in EtMe3P[Pd(dmit)2]2. Surprisingly the Hall coefficient is found to be temperature and pressure independent in the metallic state of EtMe3P[Pd(dmit)2]2, implying that the carrier number and the density of state does not change on the metal side of the Mott transition.

2015.04.14    "Dirac Cone Formation in Single-Component Molecular Conductors"  加藤 礼三
Single-component molecular conductors belong to a multi-band system where both HOMO and LUMO bands contribute to the formation of conduction bands. In most single-component molecular crystals, these two bands are separated from each other at ambient pressure, which leads to insulating properties. Application of high pressure can expand the band width for both bands and their overlap induces the conducting behavior including metallization and superconductivity. In the process of resistivity measurements and the first principles DFT calculations for single-component molecular crystals under high pressure, we noticed a possibility that the Dirac cones are formed in a crystal of dithiolene complex [Pd(dddt)2]. The Dirac cone formation in [Pd(dddt)2] can be understood by a simplified two-dimensional tight-binding model where the HOMO band is convex upward and the LUMO band is convex downward. An overlap of these two bands provides a closed intersection at the Fermi level (Fermi line) in the k-space, if there is no HOMO-LUMO interaction.
An introduction of the HOMO-LUMO interactions removes the degeneracy on the Fermi line and results in a gap formation. However, if there is a line on which the HOMO-LUMO interaction is zero, the two bands contact at the points where the line intersects with the Fermi line, leading to the formation of the Dirac cones.
In the first part of my seminar, I will introduce two pragrams (Fe2d and Bcalc) for the tight-binding band calculations.

2015.04.07    研究計画/文献紹介当番決め/一般公開ミーティング