2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
2012.03.01 平成23年度研究報告3 山本浩史、須田理行、木村弘志、圓谷貴夫
2012.02.23 "スピン流の物理と応用" 東北大学金属材料研究所 齊藤研究室 齊藤 英治
2012.02.23 平成23年度研究報告2 大島勇吾、Abdel J. Majed、山下智史、上田康平
2012.02.16 平成23年度研究報告1 草本哲郎、野村光城、田久保直子、崔亨波
2012.01.26 "Electrical Transport and Field-Effect in Molecular Monolayers" 須田 理行
Charge carriers in a field-effect transistor are confined by the gate field as a thin accumulation layer at the semiconductor-gate dielectric interface. When we use a molecular monolayer as a channel layer, the layer thickness is comparable to that of the accumulation layer. Hence, the monolayer FET, if realized, will be an ideal FET. However, most of the monolayer FETs reported so far show inverse scaling; that is, device mobility decreases dramatically with increasing channel length due to defects or limited π-π coupling between molecules.
In this seminar, I will review recent advances in monolayer FETs with long-range connectivity. The possibility to realize monolayer FET with molecular conductors will also be discussed.
2012.01.19 "Fe- and Co-based Metalladithioles" 草本 哲郎
M(dithiolene)2 complexes are composed of redox-active dithiolene ligands and transition metal ions, which exhibit multi-step redox behavior to produce interesting physical (conductivity, magnetism, NIR absorption) and chemical properties (binding-release of olefin). Ni-based dithiolene complexes such as Ni(dmit)2 anion radicals are often employed to construct molecular conductors, where p-radicals delocalized onto the conjugated dithiolene skeleton play a key role of the conductivity.
In contrast to the Ni-based dithiolenes, where they were typically in a monomeric state in a solution or a solid state, Fe- and Co-based dithiolenes tend to form dimeric molecular structures with metal-sulfur covalent bonds. Such a structural difference would reflect the different electronic structures between Ni- and Fe-based (Co-based) dithiolene complexes.
I will talk about the electronic structures, spin states, and chemical properties of Fe- and Co-based metalladithiolenes.
2012.01.12 "Photo-Induced Phenomena in Pd(dmit)2 Compounds" 田久保 直子
Pd(dmit)2 compounds show various electronic states, and have been widely studied. Specifically, photo-induced effect has been focused on in terms of charge-ordered state in the compounds. In my talk, I will review a few related studies, in which pico-second dynamics of near-infrared spectrum was observed in Et2Me2Sb[Pd(dmit)2]2 and related materials taking advantage of femto-second pulsed laser irradiation.
2011.12.22 "Quantum Criticality in Condensed Electron System" 山下 智史
Quantum critical phenomena are quite important property of condense electron system. Sometimes they reveal intrinsic properties which can not be clarified due to thermal fluctuation. The definition of quantum critical behavior is often expressed by zero-temperature transition. In contrast to this simple definition, only few examples experimental observations are reported up to now since absolute suppressions of transitions is quite difficult. It is also difficult to distinguish quantum critical phenomena from classical critical phenomena driven by thermodynamic fluctuation or other contribution. In this seminar, I will introduce famous examples of quantum critical behavior. A viewpoint for exploring quantum critical phenomena also will be discussed.
2011.12.15 "The Effect of Pressure Medium on High Pressure Measurement" 崔 亨波
It is a serious problem that how to keep hydrostatic pressure condition in high pressure electrical property measurement. Especially, the organic crystal samples are very soft, extremely sensitive with pressure.
In this seminar, I will mainly present my recent results of pressure medium effects on TTFTCNQ by diamond anvil cells. Many different kinds of liquid pressure medium have been explored up to 10 GPa. The sample dependence effects, culet size effects and uniaxial strain effect with Araldite for pressure medium will also be discussed.
2011.12.01 "Ionic Conductors in Metal Complexes" 野村 光城
Ion conductors in solid state materials have received much interest in the research fields of electrical properties and its applications of fuel and solar cells. In particular, inorganic salts, organic polymers and other organic molecules have been developed for electrochemical devices. A next generation of ion conducting materials may be derived from metal complexes.
Metal-organic frameworks (MOFs) often construct porous coordination polymers. We can prepare the MOFs by a self-assembly of molecules, and the pore size can be controlled by chemical modifications of the coordination polymer. A proton conducting channel structure (eg. water channel) can be created along the pore of MOFs. Furthermore, one could systematically synthesize some ion channel structures to show ion conduction by a supramolecular assembly of crown ether and alkali metal. When the M(crown ether) cation can be combined with Ni(dmit)2 radical anion, it can be coexistent ion and electron conducting systems. I will introduce some historical backgrounds of this research and recent topics in this research field.
2011.11.24 "High-Frequency ESR Studies on Frustrated Molecular Systems - Application to Keplerates" 大島 勇吾
I will talk about the latest high-frequency ESR studies on the Keplerate systems Mo72M30 (M=V, Cr and Fe) and its derivatives.
The Keplerates are one of the beautiful creations made by the recent development of modern chemistry [1-4]. The 30 magnetic ions of Mo72M30, which are located on each vertex of the icosidodecahedron, are antiferromagnetically coupled by the triangular and pentagonal network. As a result, this leads to a nanometer-sized cluster with huge number of states and magnetic frustrated network. Since the number of states (2S + 1)^30 can be varied by substituting the magnetic ions (2^30, 4^30 and 6^30 for M= V, Cr and Fe, respectively), it is an ideal system to study the translation from quantum to classical behavior.
For the M=Fe compound (S=5/2), 1/3-plateau of the magnetization and a broad peak in the specific heat are observed, while ESR signal shows behavior similar to the low-dimensional systems. Namely, the ESR shows a significant shift and linewidth broadening as the temperature decreases. The peak shift indicates the development of correlation inside the polyhedron, while the anomaly of the linewidth might be the indication of critical slow down towards T=0 (spin-freezing state). On the other hand, for M=V (S=1/2) compound, singlet ground state is revealed from ESR and the susceptibility measurements. For M=Cr (S=3/2), which belongs to the intermediate state, we have observed the ESR behavior similar to the M=Fe compound. More detailed ESR and specific heat results will be presented, and the ground state for each compound will be discussed.
Moreover, we have evaluated the exchange coupling constants of Mo75V20 by ESR. It is found that the ESR intensity is sensitive to the number of excited singlets and triplets. From our analysis of the ESR intensity, the exchange couplings of each triangular ring unit are 20% deformed from the regular triangle, which suggests the partial melting of the frustration in the system.
2011.11.17 "Computation based on Superconductivity" 山本 浩史
Electrons gain energy by breaking a gauge symmetry in the superconducting state. This results in the phase coherence of all electrons, which can be utilized as a tool for computations of the next-generation.
I will introduce both Qubit operation and single-flux-quantum (SFQ) operation based on superconductivity and Josephson junction technologies.
2011.10.27 "Density Functional Theory: Fundamentals and Applications for Organic Materials" 圓谷 貴夫
Density functional theory is an extremely successful approach for the description of ground state properties of solids and molecules. The main idea of DFT is to describe an interacting N-electron system via its density and not via its many-body wave function. All properties of the interacting system are a functional of the ground state charge density. Kohn and Sham show that original many body problems are replaced by independent (one-) electron problem using approximations for the exchange-correlation potential. One-electron Kohn-sham equations to describe independent Fermi particles are solved in a self-consistent way. There are several methods to solve the equations such as full-potential lienear augmented plane wave (FLAPW) and ultrasoft pseudo-potential (USPP) methods, and so on.
In this talk, basis idea of DFT and differences in these methods are explained. Recent topics of first-principles calculation methods for organic materials such as van der Waals DFT are also introduced.
2011.10.20 "Glass Transition and Molecular Dynamics on Crystal" 上田 康平
Often, glass state is thought as amorphous state which obtained by rapidly cooled liquid. However glass transition is widely observed in crystal state. It is common nature of condensed matter with any partial disorder. Temperature dependence of any physical property is bending at glass transition temperature. So existence of glass transition has large effect for low temperature property. In this seminar, I will talk about three topics.
(1) Fundamental nature of glass state. (2) What type of degree of freedom is associated to glass transition in crystal state? (3) The effect for low temperature phenomena of organic conductors.
2011.08.11 "Thermodynamic Study of Chiral Molecular-based Magnets" 福岡 修平（大阪大学大学院理学研究科化学専攻 中澤研究室）
Chirality is an important factor to control functionality of molecular-based materials. In general, the feature of chiral magnets is derived from asymmetric (chiral) crystal structures. When the crystal structure is chiral, it is expected that magnetic moments form chiral magnetic ordering. Due to this ordering, chiral magnets exhibit attracting magnetic properties and optical responses.
In this seminar, we report on results of heat capacity measurements for typical chiral molecular-based magnets [W(CN)8]4[Cu(pn)H2O]4[Cu(pn)]2・2.5H2O (pn=1,2-diaminopropane), abbreviated as W-Cu complex, using 100 ug order single crystal.
We discuss the magnetic phase transition of chiral crystals and racemic crystal through entropic analysis. We also comment on an observation of novel field-induced first order transition appears only in the H // b axis. I will talk about the possible origin of these curious magnetic behaviors in these crystals.
2011.07.28 平成23年度中間報告2 木村弘志、須田理行、山本浩史、崔亨波、Abdel J. Majed
2011.07.21 平成23年度中間報告1 大島勇吾、上田康平、草本哲郎、山下智史、野村光城、田久保直子
2011.07.14 圓谷 貴夫
"Linear Optical Properties and Electronic Structure of Electron Donor Polymers for Organic Photovoltaics"
Semiconducting polymers, like regioregular poly(3-hexylthiophene)/poly(3-hexylselenophene) (rr-P3HT/rr-P3HS) are currently the most widely studied materials in a variety of applications for polymer based bulk-heterojunction (BHJ) solar cells and organic field-effect transistors (OFET). For both applications, the performance of devices has been attributed to thin film structures of rr-P3HT/rr-P3HS on substrates.
Linear optical properties of these polymers are investigated in relation to their anisotropic crystal structure by means of first-principles density functional calculations.
The linear optical properties are evaluated by calculating its dielectric functions, focusing on the frequency dependence of the imaginary part. A group-theoretical analysis of the matrix elements is given to explain the interband transitions.
The electronic structures and optical properties are calculated using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the local-density approximation (LDA). Lastly, the differences in electronic and optical properties between rr-P3HT and rr-P3HS are discussed. Additionally, structural and electronic properties of PTB polymer which exhibits a high power conversion efficiency of 7.5% in the BHJ solar cell will be presented.
"Structural, Electronic and Magnetic Properties of Iron Hydride"
Interaction of hydrogen with transition-metal atoms is of broad interest and fundamental importance for understanding the properties of hydrogen-storage materials.
Iron and its hydrides under ultrahigh pressure at giga pascal range are also interesting for geophysics and planetary science since Fe and H are main constituents of the Earth’s core. Iron hydride FeH has double hexagonal close-packed (dhcp) Fe lattice. Structural transformation from bcc Fe to dhcp FeH has been observed under hydrogen pressure above about 3.5 GPa. The hydride is thermodynamically stable only at high-pressure condition and rapidly decomposed into bcc Fe and gaseous hydrogen under ambient condition.
Fortunately, the hydride can be retained in a meta-stable state at ambient pressure by cooling under high hydrogen pressure. The “quenched” meta-stable FeH shows a ferromagnetic phase with dhcp Fe lattice. Magnetic properties are very sensitive to external variables such as pressure. To investigate the magnetic properties of the hydride depending on applied hydrogen pressure, an x-ray magnetic circular dichroism measurement at the Fe K-edge has been carried out recently.
In this study, we present a theoretical investigation of FeH for understanding the structural, electronic and magnetic properties from first-principles calculations.
2011.06.30 "Organic-based Magnets: New Chemistry, New Physics, and New Materials for this Millennium" J. S. Miller
Molecule-based materials exhibiting the technologically important property of bulk magnetism have been prepared and studied in collaboration with many research groups worldwide frequently exhibit supramolecular extended 3-D structures. These magnets are prepared via conventional organic synthetic chemistry methodologies, but unlike classical inorganic-based magnets do not require high-temperature metallurgical processing. Furthermore, these magnets are frequently soluble in conventional solvents (e. g., toluene, dichloromethane, acetonitrile, THF) and have saturation magnetizations more than twice that of iron metal on a mole basis, as well as in some cases coercive fields exceeding that of all commercial magnets (e.g., Co5Sm). Also several magnets with critical temperatures (Tc) exceeding room temperature have been prepared. In addition to an overview of magnetic behavior, numerous examples of structurally characterized magnets made from molecules will be presented. Our groups has discovered 7 families of molecule-based magnets, mostly organic-based, and have significantly contributed to an eight family based upon the Prussian blue structure. Four examples magnetically order above room temperature and as high at 127 oC. These will include [MIII(C5Me5)2][A], [MnIII(porphyrin)][A] (A = cyanocarbon etc. electron acceptors) as well as M[TCNE]x, which for M = V is a room temperature magnet that can be fabricated as a thin film magnet via Chemical Vapor Deposition (CVD) techniques. A newer class of magnets of [Ru2(O2CR)4]3[M(CN)6] (M = Cr, Fe; R = Me, t-Bu) composition will also discussed. For R = Me an interpenetrating, cubic (3-D) lattice forms and the magnet exhibits anomalous hysteresis, saturation magnetization, out-of-phase, Χ"(T), AC susceptibility, and zero field cooled-field cooled temperature-dependent magnetization data. This is in contrast to R = t-Bu, which forms a layered (2-D) lattice. Additionally, new magnets possessing the nominal Prussian blue composition, M'[M(CN)6]x and (Cation)yM'[M(CN)6], but not their structure, will be described.
2011.06.23 "Control of Magnetic Properties in Molecular Solids by External Photo-Stimuli" 須田 理行
Since the first discovery of photo-controllable magnetic compounds, so called CoFe Prussian blue, in 1996, optically-switchable magnetic materials have been attracting great interest because of the continuing demand which is driving the development of future optical memory and switching devices. Until now, various types of photo-magnetic effects, such as photo-induced (de)magnetization and photo-induced magnetic pole inversion, have been realized mainly in kinds of metal cyanide complexes (Prussian blue analogues). In this seminar, I will introduce some important works not only in the metal cyanide systems but also in organic radicals or inorganic systems.
2011.06.16 "Next Generation of Magnetic Molecular Conductors" 草本 哲郎
Since molecular conductors have ionic characters, which are composed of cation (or anion) radicals and the counter ions, it is possible to introduce another physical property into the system by using a functional counter ion. Magnetic molecular conductors are good examples, in which an introduction of the magnetic counter ion realizes a co-existence of conductivity and magnetism in one system. (BETS)(FeX)4 (X = Cl, Br) are one of the interesting magnetic molecular conductors, in which the interplay between conducting π-electron on BETS and localized d-electron on FeX4 produces intriguing physical properties such as a field-induced superconductivity.
While (BETS)(FeX)4 salts have attracted scientists more than 10 years, chemists continue to make efforts to develop new types of magnetic molecular conductors using 'functional' magnetic counter ions, such as a spin-crossover (SCO) complex and a single-molecule magnet (SMM).
I will introduce recent advances of these magnetic molecular conductors with 'functional' magnetic counter ions, namely, the next generation of magnetic molecular conductors.
2011.06.09 "High Pressure Techniques for Physical Properties Measurement" 崔 亨波
It is needless to say that, the high pressure technique is a very important and powerful method of research material science. Especially, for molecular conductors because these materials have soft lattice structure, the physical properties are easily affected by external pressure. However, it is very difficult and dangerous to start without any basic knowledge of high pressure.
In this seminar, I will introduce a lot kind of high-pressure apparatuses used for physical properties research in the world. The techniques such as sample set-up, selection of pressure transmitting medium, and pressure calibration method are also included.
2011.06.02 "Electronic Ferroelectricity" Abdel J. Majed
Beyond the standard classification of ferroelectrics, it is known that, in some types of ferroelectric materials, electron degrees of freedom and/or electronic interactions directly give rise to a macroscopic electric polarization and ferroelectric transition. Here, we call this phenomenon electronic ferroelectricity and these materials electronic ferroelectric compounds. There are the two types of the electronic ferroelectricity; 1) spin driven ferroelectricity where magnetic interaction and magnetic ordering mainly cause the ferroelectric transition and 2) charge driven ferroelectricity where electronic charge degree of freedom and charge order are responsible for an electric polarization. In this seminar, I will review our current understanding of materials that exemplify both type of electronic ferroelectricity.
2011.05.26 "Photo-Induced Neutral to Ionic Phase Transition in TTF-CA" 田久保 直子
Photo-induced phase transition (PIPT) has been studied since around 1990. A wide variety of PIPT has been observed with recent developments of ultrafast time-resolved measurements. In this seminar, I will review photo-induced neutral to ionic phase transition in TTF-CA, which has been widely studied since 1990 using various time-resolved measurements. I will also inform you about the most recent topic "photo-induced superconductivity".
2011.05.13 研究会「金属 dmit 錯体による磁性・伝導性研究の最前線」
2011.04.28 "Proton Tunnel and Hydrogen Bond Network" 上田 康平
The approximation that nuclei are dealt as classical particles is almost all good for representing physical and chemical phenomena. However the quantum nature of proton is enhanced under special condition. For example, the quantum nature of the proton transfer within hydrogen-bond network is open to a particularly interesting problem. I measured any hydrogen bond network system on crystalline state by calorimetry and dielectric measurement with changing its size, strength and dimension. In this seminar, I introduce extraordinary change of quantum behavior of proton transfer and a new phenomenon brought by increase hydrogen bond network size.