RIKEN's CMM


2019 2018 2017 2016 2015 2014 2013 2012 2011 2010 2009 2008 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" S. Sugiura (M2, Department of Physics, Faculty of Science, Toho University) 2015.1.22 "Nitrogen-Vacancy in Diamond for Nanoscale Imaging" F. Iwase 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" Y. Kawasugi 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" T. Tsumuraya 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 Literature Survey Report 2014.12.11 Literature Survey Report 2014.12.04 "Ferromagnetic Superconductors" H. B. Cui 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" Dr. N. Tajima (Associate professor, Department of Physics, Faculty of Science, Toho University) 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" Y. Oshima 2014.11.13 "Organic Thin Films" S. Fujiyama 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 "TBA" Dr. Yoshitomo Kamiya（Condensed Matter Theory Laboratory, RIKEN） 2014.10.23 "Phase Diagram of the Mott Transition in EtMe₃P[Pd(dmit)₂]₂ and the bad metal state" Dr. Abdel Jawad Majed（Advanced Meson Science Laboratory, Nishina Center for Accelerator-Based Science, RIKEN） 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" H. Oike（Dynamic Emergent Phenomena Research Unit, Cross-Divisional Materials Research Program, Center for Emergent Matter Science, RIKEN） 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 Literature Survey Report 2014.10.02 Midterm Report 5 Y. Oshima, S. Fujiyama 2014.09.19 "Zero-Gap State in Organic Conductor from the Topological Aspect" Dr. J. Suzumura (Professor emeritus at Nagoya university) 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 Conference Presentation Practice and Midterm Report 4 Y. Sato, F. Iwase, T. Tsumuraya, Y. Kawasugi, K. Ueda 2014.07.24 Midterm Report 3 H. B. Cui, K. Ueda 2014.07.17 Midterm Report 2 F. Iwase, T. Tsumuraya 2014.07.10 Literature Survey Report 2014.07.03 Midterm Report 1 H. B. Cui, Y. Sato 2014.06.26 Presentation by Dr. T. Kusamoto and trainees "Structural and Magnetic Properties of Cu(II) and Zn(II) Complexes with an Organic Radical PyBTM as Ligands" T. Kusamoto 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" H. Hattori 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" A. Tanushi 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 Dr. T. Takenobu（Takenobu Lab., Waseda Univ.） 2014.06.12 "Single Component Molecular Conductors" H. B. Cui 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" Y. Kawasugi 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" F. Iwase 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 "TBA" Dr. T. Konoike 2014.05.15 "Local Electrostatic Imaging of Buried Electron Gas at Interface Using Scanning Single-Electron Transistor" Y. Sato 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" Dr. H. Seo（Condensed Matter Theory Lab., RIKEN） 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 Literature Survey Report 2014.04.17 Research Plan of FY2014 2014.04.03 "Luminescent Organic Radicals" Dr. T. Kusamoto（Inorganic Chemistry Lab., The University of Tokyo） 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.