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2014.03.20 FY2013 Annual Report 4 S. Fujiyama, Y. Oshima
2014.03.13 "Orbital Degree of Freedom in a Molecular Crystal" Dr. H. Sawa （Sawa Lab., Nagoya University）
The molecular crystal is a unique material by the ability of exotic physical properties to be described by the interaction which assumed a molecule or a dimer of molecules to be one site. However, in order to understand the relation between the diversity of molecules and their variegated physical properties, the information on a spatially spreading frontier orbital is indispensable. If you use the Synchrotron X-ray diffraction data of a single crystal which has the wide dynamic range of the intensity and high Q-resolution, the electron density distribution on the molecule can be obtained precisely.
In this seminar, I would like to talk about the recent results of the electronic charge distribution of typical molecular conductors and the latest analysis result about the Pd(dmit)2 system which shows the interesting physical properties containing a quantum spin liquid by viewpoint of the molecular orbital degree of freedom.
2014.03.06 FY2013 Annual Report 3 H. B. Cui, Y. Kawasugi
2014.02.27 FY2013 Annual Report 2 F. Iwase, K. Ueda
2014.02.20 FY2013 Annual Report 1 T. Tsumuraya, Y. Sato
2014.02.13 Literature Survey Report
2014.02.06 "Direct Observation of the Photoinduced Dynamics of the Electronic and Lattice Structural Change in Me4P[Pt(dmit)2]2" Dr. T. Ishikawa（Koshihara Okimoto Lab., Tokyo Insitute of Technology）
Development of the fs-laser technology enables us to observe ultrafast dynamics of photoinduced phenomena with precise time-resolution. However, among the various time-resolved measurement techniques, the only optical measurement could achieve the time-resolution of the order of sub-ps range. Recently, it bacame possible to use another new and powerful experimental technique, time-resolved electron diffraction, which can achieve the time-resolution of sub-ps scale with using table-top measurement system.
This time-resolution is comparable to the optical one, then we can directly study the dynamics from the both side of viewpoints, electronic and lattice (molecular) structural change. Using the both experimental technique, optical spectroscopy and electron diffraction, we must be able to make the various photoinduced dynamics clearer.
Now we are studying the dynamics of photoinduced phase transition from the charge-separated phase in Me4P[Pt(dmit)2]2.
In this seminar, I would like to talk about the recent results of both time-resolved optical and electron diffraction measurement about this unique system.
2014.01.31 "Universality Class Of The Mott Transition In EtMe3P[Pd(dmit)2]2" Abdel Jawad Majed
The universality class of the Mott transition is currently an unresolved problem. In this seminar, I will present isothermal pressure measurements of the conductivity and the thermoelectric coefficient within a Helium pressure medium in EtMe3P[Pd(dmit)2]2, a dimer-Mott insulator. The thermoelectric coefficient is of particular interest as the Mott-transition is clearly seen in this compound. Scaling of the conductivity and the thermoelectric coefficient, on both the insulating and the metal side, will be shown and compared to previous results in other Mott insulators.
2014.01.23 "TBA" Dr. Hattori
2014.01.16 "Dielectric and Optical Properties in Dimer-Mott Insulator" Dr. M. Naka（Quantum Matter Theory Research Team, Strong Correlation Physics Division, Center for Emergent Matter Science, RIKEN）
It is widely known that electric polarization in some kinds of materials is attributed to the charge order without inversion symmetry. This is seen in some transition metal oxides and charge transfer salts. Quasi two-dimesional organic salt kappa-(ET)2Cu2 (CN)3 belongs to this kind of materials. Two ET molecules construct a dimer and are arranged on a triangular lattice. Recently, it is reported that a relaxor-like dielectric anomaly and a low energy charge excitation in THz region are experimentally observed. An origin of them is thought to be a “dimer dipole” generated by a localized hole in one side of the ET molecules in dimers. Motivated by this result, we study dielectric and optical properties in kappa-type ET salts where the internal charge degree of freedom in a dimer exists. We adopt various models, extended Hubbard model, spinless fermion model and these low-energy effective models for analysis without ambiguity. We analyze these models by utilizing mean-field approximation, Monte Carlo method, exact diagonalization method and spin wave approximation, and focus on the dielectric and optical responses due to the “dimer dipoles”. In finite temperature, dimer-Mott (DM) and ferroelectric charge ordered (FCO) phases compete with each other. We investigate the temperature dependence of dielectric susceptibility, and find the anomaly with broad peak structure around the boundary of DM and FCO phases. Also, we find the low-energy intra-dimer charge excitations which show strong light polarization dependence. The charge excitation mode which is observable by light being parallel to the electric polarization shows remarkable softening and frequency dispersion near the phase boundary, and is expected to be a collective charge excitation.
2014.01.09 "Field Effect Control of Electronic Phases in Strongly Correlated Oxides" Dr. T. Hatano（Emergent Device Research Team, Center for Emergent Matter Science, RIKEN）
In strongly correlated oxides, the mutual interactions among charge, spin, orbital degrees of freedom make a rich variety of orderings which have been controlled by external stimuli such as a magnetic fields, light and pressure. However, the electric field effect, which is of critical importance for the electronics applications, has been left to be investigated because of the insufficient strength of electric field in conventional field effect transistors (FET). To overcome this point, we employed an electric double-layer transistor (EDLT), i.e. an ionic liquid-gated FET, which can produce the extremely strong electric field.
In this seminar, I will introduce the recent results for the oxide-based EDLT. Most focus will be on the perovskite manganites-EDLT: dual control of the doping level and one-electron bandwidth by the gate voltage and magnetic field, respectively, enables us a gigantic resistance switching with a slight tweaking of the gate voltage.
2013.12.26 Literature Survey Report
2013.12.19 "Potential Energy Surface of Very Short Hydrogen Bonds" K. Ueda
Recently, New interesting molecular conductor, H3- (Cat-EDT-TTF)2, was synthesized. H3- (Cat-EDT-TTF)2 shows interesting phase behavior by deuteration; quantum spin liquid state for H compound and charge ordered non magnetic phase for D compound. In the crystalline, two Cat-EDT-TTF molecules are connected with very short hydrogen bond, and this hydrogen bond has got to plays key role for magnetic and electric nature of it. At the studying field of hydrogen bonded (anti-)ferroelectric, such very short hydrogen bond was attracted and studied widely, because of existence of large isotope effect and quantum para electricity. Especially, local symmetry of potential energy surface of proton and proton-phonon coupling were discussed.
In this seminar, I will introduce 30 years desiccations of intra-dimer very short hydrogen bond of M3H(XO4)s, in which (XO4) is connected with 2.5 angstrom hydrogen bond.
2013.12.12 "Covalent Nature of Hydrogen Bonds in Functional Molecular Materials" T. Tsumuraya
Several organic ferroelectric materials having hydrogen bond were found recently, in which the H-bonds are thought to have a large contribution to the spontaneous polarization. Horiuchi et al. synthesized H-bonded organic ferroelectrics such as phenazine-chloanil acid (Phz-H2ca) and croconic acid. The ferroelectricity is induced by displacement of H atom between molecule, and they show a relatively large spontaneous polarization among organic ferroelectric materials.
In this talk, we discuss covalent nature of the H-bond with short O--O and O--N distances in related to the realization of the ferroelectricity. Similar intermolecular H-bond in other functional materials are also reported.
2013.12.05 "Superconducting Chemical Elements under High Pressure" H. B. Cui
In this seminar, I will present the high pressure research fields in Japan. The first topic is, the recent progress in high pressure physics and technology. The second topic is, the efforts on pressure induced superconductor works in the chemical elements on the Periodic table. The back ground and recent results in dense hydrogen, Oxygen, Lithium, and Calcium will be introduced.
2013.11.28 "High Magnetic Field Studies on Molecular-based Nano-magnets" Y. Oshima
Here, in my seminar, I will talk about my old studies on molecular-based nano-magnets, such as single molecule magnet, single chain magnet. Firstly, I will introduce the definition of "high" magnetic field and why we need it to study the nanomagnets. Then, I will talk about the basics of the single molecule magnet and the single chain magnet. I will also try to explain why such magnets are interesting from a physicist’s point of view (which is usually different from the chemists’ point of view) .
2013.11.21 "Magnetic X-Ray Diffraction (on molecular materials)" S. Fujiyama
Magnetic x-ray diffraction is a relatively new technique to exploit the magnetism of solids, which offers several advantageous points such as q-dependent spin dynamics as well as site selectivity. There has been no study of magnetic x-ray diffraction on molecular materials so far, and I show the characteristics and technical limitations of the technique, and discuss possible applications on molecular materials.
2013.11.14 "Field-Effect Measurements Using Electrolyte Gating" Y. Kawasugi
Field-effect carrier doping with electrolyte gating has attracted much attention recently. This method is applicable to a wide range of materials and enables high-density carrier injection, resulting in interesting phenomena such as field-induced superconductivity, ferromagnetism, and spin manipuration. Recent publications and attempts of application to molecular conductors will be introduced.
2013.10.30 "Thermodynamic Study on the Magnetic Property of X[Ni(dmit)2]2 with bi-layer Structure" Mr. R. Yoshimoto (Nakazawa Lab., Osaka University)
A part of X[Ni(dmit)2]2 system (X=Me3,5-DIP, Et-4BrT, Et-2I-5BrP) has interesting crystal structure called "bi-layer structure" due to asymmetric interaction of cations. In these compounds, two different types of Ni(dmit)2 layers are formed. In the case of (Me-3,5-DIP)[Ni(dmit)2]2, one Ni(dmit)2 layer behaves as metallic layer and the other layer behaves as Mott insulating layer. In (Et-4BrT)[Ni(dmit)2]2 and (Et-2I-5BrP)[Ni(dmit)2]2, a metallic behavior was not observed. Both Ni(dmit)2 layers are considered as Mott insulating layer with different molecular alignment to each other. It was suggested that the magnetic properties of these compounds were different from ordinary Mott insulator system by various measurement. However, the detailed properties were still mysterious.
In this seminar, I will introduce the heat capacities of three types of bi-layer compounds which may give us a key point of magnetic property of bi-layer system. I will discuss the drastic transition behavior lower than 1 K in (Et-4BrT)[Ni(dmit)2]2 and (Et-2I-5BrP)[Ni(dmit)2]2. I also investigated on the relation between the heat capacity behavior and field dependence of magnetic susceptibility. The heavy fermion like behavior in (Me-3,5-DIP)[Ni(dmit)2]2 will be also introduced. I also suggest the possibility of important rolls of the weak interaction such as inter-layer interaction in these bi-layer systems.
2013.10.24 "Substrate Effect on the Electronic Properties of Graphene" Y. Sato
Graphene continues to attract much interest due to its unique massless Dirac fermion electronic feature and potential application as a flexible post-silicon electronic material. Its atomic thickness, however, makes graphene so sensitive to environment that the interaction with supporting substrate sometimes makes it difficult to realize truly intrinsic properties of graphene. In this seminar, I will review several substrate effects on graphene recently found, especially focusing on the following two: (i) the external screening by dielectric substrate, which varies carrier scattering by charged impurity, electron-electron interaction, and electron-phonon coupling, (ii) π-band reshaping by precise control of the alignment between graphene and the substrate material such as hexagonal boron nitride (h-BN).
2013.10.17 Research Outline T. Kusamoto, Y. Hattori, L. Shi, A. Tanushi
2013.10.10 "Resistively Detected NMR in Quantum Hall State" F. Iwase
Nuclear magnetic resonance (NMR) is a powerful technique to study molecular structure and electronic properties in bulk crystals. In recent years, novel surface states in topological insulator (superconductor) and interfaces in FET or heterojunction structure have attracted much attention. The contribution of NMR to these fields, however, is limited, since the standard NMR is not sensitive to the surface state due to the small volume (and also small number of nuclei/electrons). In the seminar, I introduce an experimental technique called resistively detected nuclear magnetic resonance (RDNMR), which has the possibility to avoid such problem and has been originally applied to a quantum Hall effect (QHE) in GaAs heterostructure. The principle of NMR and the basic concept of QHE are introduced. Then, the difference between NMR and RDNMR is highlighted. A RDNMR evidence of low energy excitations in the quantum Hall state (Skyrmion) is discussed.
2013.10.03 Literature Survey Report
2013.09.19 Midterm Report 3 S. Fujiyama, Y. Oshima
2013.09.12 Midterm Report 2 Y. Kawasugi, F. Iwase, Y. Sato
2013.09.05 Midterm Report 1 H. B. Cui, K. Ueda, T. Tsumuraya
2013.07.25 "Organic Field Effect Transistors under High Pressure" Dr. K. Sakai (Takeya Lab., Tokyo University)
Organic molecular semiconductors have been known as flexible electronic materials since microscopic molecular arrangement inside crystal is based on weak van der Waals interaction, resulting in sensitivity against external mechanical stimulation. This fact should be paid attention in that physical and chemical properties can be tuned by pressure.
In this presentation, I introduce current investigation about the pressure effect in organic semiconducting materials, progressed by the combination of carrier transport measurement in organic field effect transistors and crystal structure analysis. In every case it is clarified that variation of charge transfer rate according to pressurization is governed by not only reduction of intermolecular distance but change in relative alignment of adjacent molecules coming from the peculiar shape of molecule.
2013.07.11 Literature Survey Report
2013.07.04 "Towards a Precise First-Principles Vibration Frequencies of Molecular Crystals with Density Functional Theory" T. Tsumuraya
To accurately calculate vibration frequencies of molecular crystals is a great challenge because these vibrations are results from interplay among various types of interactions such as chemical bondings, hydrogen bonding, dipole-dipole, Van der Waals, and electrostatic interactions.
Especially, low-frequency vibration modes measured by Terahertz spectroscopies have soft potential energy surfaces. One of the major approximation arises in DFT is the choice of an approximation in exchange and correlation density-functional.
In this part, local and semi local functionals such as local density approximation (LDA) and generalized gradient approximation (GGA) that has been used in standard choice of the first-principles calculations.
Recently, it has been demonstrated that non-local functionals, such as that by Heyd-Scuseria-Ernzerhof (HSE) which contains exact exchange shows better descriptions of band gaps, phonon dispersion, and so onor one with dispersion interactions, such as vdW-DF2 significantly improve the equilibrium lattice parameters of molecular crystals.
These functionals could be suitable for obtaining vibration modes of molecular conductors.
In this talk, we discuss the effect of these approximations with non-local potential in vibration modes and thermodynamic properties for crystalline molecular systems.
2013.06.27 "TBA" Dr. H. Eguchi (Advanced Applied Science Department, Research Laboratory, IHI Corporation)
We have found that this magnetic organic compound (EI236) exhibits anti-cancer property and, more important, possesses a magnetic property as it was readily attached to a magnet. EI236 inhibited melanoma expansion in mouse tails when delivered to the melanoma lesion using a commercially available magnet. The local accumulation of the compound, as induced by a magnet, was readily visualized by magnetic resonance imaging (MRI) in mice. Thus, this acted as both an anti-cancer drug and an MRI contrast, and had pharmacological effects that could be delivered in a controlled manner. The identification of such compounds may dramatically alter our concept of pharmacotherapy in the future, i.e., drug-targeting using a magnet and drug-dosing using MRI.
2013.06.20 "Nonlocal Spin Valve Measurements on Organic Materials" Y. Kawasugi
Application of organic materials to spintronics has been widely studied in this decade because of their long spin lifetime, particularly since the pioneering report of organic spin valves in 2004. However, the four-terminal "nonlocal" spin valve measurement, which can detect pure spin current and exclude spurious signals, had not been carried out in organic spin valves. I will introduce the nonlocal spin valve measurement in lateral spin valve devices using highly conducting organic materials, conducting polymers and molecular conductors.
2013.06.13 "Pressure Effect on Iron-based Inorganic Compounds" H. B. Cui
Since the discovery of superconductivity in LaFeAsO1-xFx at 2006, a tremendous numbers of iron-based superconductors have been synthesised. Many scientists found there are two methods could enhance Tc. The one method is, a doping of fluoride ions at the O2- sites in LaOFeAs could increase Tc up to 55 K. Another method is, increase pressure in Sr2VFeAsO3 could enhance Tc up to 46 K (at 4 GPa).
In this seminar, I will introduce the history of iron-based superconductors and recent high pressure transport measurement results. The Fe-P or As compounds, Fe- S, Se, Te compounds will be mainly presented.
2013.05.30 "How to Use Differential Scanning Calorimeter and how to Analysis Heat Capacity" K. Ueda
The value of transition entropy, which is detected by thermal measurement, supplies important microscopic information; for example, transition type, spin ordering way. Recently, we can measure heat capacity easily using with commercial calorimeter; PPMS, DSC, AC-DCS….
However, there are some serious maladies from popularize, and some poor data and analysis are published. Thus, in this seminar, I will talk about how to measure heat capacity with ?1% actually by commercial DSC(Differential scanning calorimeter) and how to analyze heat capacity data of crystal; especially, determining and subtracting lattice heat capacity, which cover some important anomalous behavior.
2013.05.23 "Electrically Controllable Adsorption of Oxygen on Graphene Devices" Y. Sato
Since the emergence of graphene, an atomically thin graphite sheet, much attention has been attracted for the unique features of two-dimensional (2D) materials that cannot be seen in conventional materials. One of the central topics is how to control the physical properties of them; an effective approach is adsorption of guest molecules on the host 2D materials taking advantage of high sensitivity of them to charges, spins, and chemical interactions on the surface.
In this seminar, I will present my past works focusing on the electron transport of the graphene. oxygen host.guest interacting systems, where the adsorbed oxygen serves not only as electron acceptor but also as molecular magnet with triplet spin. It will be shown that the impact of oxygen adsorption can be significantly modified by external electric field and temperature control, and especially, field dependence of the adsorption kinetics is nicely accounted for considering relation between charge transfer rate and the Fermi level of graphene.
I will also explain the novel concepts of “effective electron temperature”, which have turned out to be essential to describe charge transfer process between the guest molecules and the host thin-layer materials in the device (e.g. field effect transistor) structure.
2013.05.16 "Low Energy Dynamics in Neutral-Ionic Phase Transition Materials" F. Iwase
Quantum criticality has been studied extensively in the context of superconductivity and non-Fermi liquid behavior in high-Tc cuprate and heavy fermion. In one-dimensional mixed-stacked organics, some materials show a change of the bonding states due to a charge transfer between electron-donor molecule and electron-acceptor molecule. This is called neutral-ionic phase (NI) transition. A simultaneous spin-Peierls-like dimeric lattice-distortion forms the ferroelectric one-dimensional chains. DMTTF-QBr4-nCln is a candidate for the study of the NI quantum criticality. The 2,6-QBr2Cl2 salt, which is located near the NI boundary (TNI〜0 K), shows a Barrett type quantum paraelectric behavior in the dielectric constant.
In the seminar, I will show the systematic study of the critical behavior and the evolution of the low energy dynamics, detected by Cl and Br NQR using helium-gas as the pressure medium.
2013.05.09 Literature Survey Report
2013.04.25 "Marginal Mott Behavior of Jeff=1/2 Iridates Srn+1IrnO3n+1 Evidenced by Magnetic X-Eay Scattering" S. Fujiyama
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2013.04.18 "Unusual Magnets From Metal-Organic Frameworks and Minerals" Dr. Mohamedally Kurmoo, Universite de Strasbourg
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2013.04.11 Research Plan of FY2013
