The Experts below are selected from a list of 4578 Experts worldwide ranked by ideXlab platform
Kazushi Kanoda - One of the best experts on this subject based on the ideXlab platform.
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disorder unveils mott quantum criticality behind a first order transition in the quasi two dimensional Organic Conductor κ et 2 cu n cn 2 cl
Physical Review B, 2019Co-Authors: Mizuki Urai, Kazuya Miyagawa, Takahiko Sasaki, Tetsuya Furukawa, Yasuhide Seki, Hiromi Taniguchi, Kazushi KanodaAbstract:We show the significant impact of weak disorder on the Mott transition by investigating electronic transport in a systematically x-ray-irradiated layered Organic Conductor under continuous pressure control. The critical end point of the first-order Mott transition is dramatically suppressed by such weak disorder that causes only a minor reduction in the transition temperature of disorder-sensitive nodal superconductivity. Instead, quantum critical scaling of resistance holds at lower temperatures and Fermi-liquid coherence temperature on the metallic side is lowered. Introducing disorder unveils the interaction-induced quantum criticality hidden behind the first-order transition.
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Observation of an anisotropic Dirac cone reshaping and ferrimagnetic spin polarization in an Organic Conductor
Nature Communications, 2016Co-Authors: Michihiro Hirata, Masafumi Tamura, Kazuya Miyagawa, Akito Kobayashi, Kyohei Ishikawa, Claude Berthier, Denis Basko, Genki Matsuno, Kazushi KanodaAbstract:The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping. In less symmetric Dirac materials possessing anisotropic cones with tilted axes, the Coulomb interaction can provide still more exotic phenomena which have not been experimentally unveiled yet. Here, using site-selective nuclear magnetic resonance, we find a non-uniform cone reshaping accompanied by a bandwidth reduction and an emergent ferrimagnetism in tilted Dirac cones that appear on the verge of charge ordering in an Organic compound. Our theoretical analyses based on the renormalization-group approach and the Hubbard model show that these observations are the direct consequences of the long-range and short-range parts of the Coulomb interaction, respectively. The cone reshaping and the bandwidth renormalization, as well as the novel magnetism revealed here, can be ubiquitous and vital for many Dirac materials.
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charge cluster glass in an Organic Conductor
Nature Physics, 2013Co-Authors: Fumitaka Kagawa, Taku J Sato, Kazuya Miyagawa, Kazushi Kanoda, Yoshinori Tokura, Kensuke Kobayashi, Reiji Kumai, Youichi MurakamiAbstract:Geometrically frustrated spin-systems do not order magnetically even at absolute zero, forming instead a spin liquid or a glassy state. An Organic Conductor in which the charges, rather than spins, are frustrated now shows a similar absence of long-range order, resulting in a charge-cluster glass at low temperature.
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13 c nmr study on the charge disproportionated conducting state in the quasi two dimensional Organic Conductor α bedt ttf 2 i 3
Physical Review B, 2011Co-Authors: Michihiro Hirata, Kazushi Kanoda, Kazuya Miyagawa, Kyohei Ishikawa, Masafumi TamuraAbstract:The conducting state of the quasi-two-dimensional Organic Conductor $\ensuremath{\alpha}$-(BEDT-TTF)${}_{2}$I${}_{3}$ at ambient pressure is investigated with ${}^{13}$C NMR measurements, which separate the local electronic states at three nonequivalent molecular sites (A, B, and C). The spin susceptibility and electron correlation effect are revealed in a locally resolved manner. While there is no remarkable site dependence around room temperature, the local spin susceptibility gradually disproportionates among the nonequivalent sites with decreasing temperature. The disproportionation ratio yields 5:4:6 for A:B:C molecules at 140 K. Distinct site and temperature dependences are also observed in the Korringa ratio ${\mathcal{K}}_{i}\ensuremath{\propto}{(1/{T}_{1}T)}_{i}{K}_{i}^{\ensuremath{-}2}$ ($i$ = A, B, and C), which is a measure of the strength and the type of electron correlations. The values of ${\mathcal{K}}_{i}$ point to sizable antiferromagnetic spin correlation. We argue the present results in terms of the theoretical prediction of the peculiar site-specific reciprocal-space ($\mathbit{k}$-space) anisotropy on the tilted Dirac cone, and discuss the $\mathbit{k}$-dependent profiles of the spin susceptibility and electron correlation on the cone.
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unconventional critical behaviour in a quasi two dimensional Organic Conductor
Nature, 2005Co-Authors: Fumitaka Kagawa, Kazuya Miyagawa, Kazushi KanodaAbstract:Changing the interactions between particles in an ensemble--by varying the temperature or pressure, for example--can lead to phase transitions whose critical behaviour depends on the collective nature of the many-body system. Despite the diversity of ingredients, which include atoms, molecules, electrons and their spins, the collective behaviour can be grouped into several families (called 'universality classes') represented by canonical spin models. One kind of transition, the Mott transition, occurs when the repulsive Coulomb interaction between electrons is increased, causing wave-like electrons to behave as particles. In two dimensions, the attractive behaviour responsible for the superconductivity in high-transition temperature copper oxide and Organic compounds appears near the Mott transition, but the universality class to which two-dimensional, repulsive electronic systems belongs remains unknown. Here we present an observation of the critical phenomena at the pressure-induced Mott transition in a quasi-two-dimensional Organic Conductor using conductance measurements as a probe. We find that the Mott transition in two dimensions is not consistent with known universality classes, as the observed collective behaviour has previously not been seen. This peculiarity must be involved in any emergent behaviour near the Mott transition in two dimensions.
Yoshikazu Suzumura - One of the best experts on this subject based on the ideXlab platform.
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anomalous conductivity of two dimensional dirac electrons in Organic Conductor under pressure
Journal of the Physical Society of Japan, 2021Co-Authors: Yoshikazu Suzumura, Masao OgataAbstract:The electric conductivity of Dirac electrons in the Organic Conductor α-(BEDT-TTF)2I3 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] under pressure has been examined using a two-dimensional tig...
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effect of tilting on the in plane conductivity of dirac electrons in Organic Conductor
Journal of the Physical Society of Japan, 2014Co-Authors: Yoshikazu Suzumura, Igor Proskurin, Masao OgataAbstract:We examine the in-plane electric conductivity of Dirac electrons with a tilted cone in terms of the degree of the tilting η and the angle α measured from the applied electric field. It is demonstrated that a noticeable difference in the conductivity exists between α = 0 and π/2, which corresponds to the tilting being parallel and perpendicular to the field, respectively. With increasing tilting parameter η (0 ≤ η 0 for π/2 < α < π. We propose an experiment to determine α and η.
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inversion symmetry and wave function nodal lines of dirac electrons in Organic Conductor alpha bedt ttf _2i_3
arXiv: Mesoscale and Nanoscale Physics, 2013Co-Authors: Frederic Piechon, Yoshikazu SuzumuraAbstract:By examining Organic Conductor alpha-(BEDT-TTF)_2I_3 which is described by a nearest neighbors tight-binding model it is shown that because of inversion symmetry, each component of a wave function (WF) exhibits nodal lines (NLs) in the Brillouin zone. In the absence of any band crossing, each NL connects two time reversal invariant momenta (TRIM) as partners. In the presence of a pair of Dirac points (band crossing), for each band that crosses and for each WF component there is a NL that connects the pair of Dirac points via a TRIM without partner. This second kind of NL leads to a discontinuous sign change for non vanishing components of the WF. Such a property is at the origin of the +/- pi Berry phase accumulated on a contour integral encircling one Dirac point. The results are examplified by numerical calculation of WFs components for the above Conductor with a 3/4 filled band.
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dirac electron in Organic Conductor α bedt ttf 2i3 with inversion symmetry
Journal of the Physical Society of Japan, 2013Co-Authors: Frederic Piechon, Yoshikazu SuzumuraAbstract:Diffraction data at ambient pressure and room temperature for the Organic Conductor α-(BEDT-TTF)2I3 have shown the existence of an inversion symmetry between the molecular sites A and A'. This prop...
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mechanism of dirac point in α type Organic Conductor under pressure
Journal of the Physical Society of Japan, 2013Co-Authors: Yoshikazu Suzumura, Takao Morinari, Frederic PiechonAbstract:We examine the Dirac point of α type Organic Conductor described by a tight binding model with a \(4\times 4\) matrix. The Dirac point between a conduction band and a valence band, is calculated wi...
Gunzi Saito - One of the best experts on this subject based on the ideXlab platform.
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high pressure transport study of a charge transfer salt based on cytosine and tcnq using a diamond anvil cell
Journal of Physics: Conference Series, 2008Co-Authors: Masafumi Sakata, Mitsuhiko Maesato, Takafumi Miyazaki, Kazukuni Nishimura, Tsuyoshi Murata, Hideki Yamochi, Gunzi SaitoAbstract:Transport properties of a strongly correlated Organic Conductor (CHC+)TCNQ− were examined under high pressures up to about 7 GPa using a diamond anvil cell, where CHC+ denotes hemiprotonated cytosine pair and TCNQ represents 7,7,8,8-tetracyanoquinodimethane. This salt is a highly conductive semiConductor as a fully ionic TCNQ salt with the activation energy Ea of 0.14 eV at ambient pressure. Application of high pressure gradually increased the conductivity. The Ea decreased monotonically by a rate of 0.013 eV/GPa.
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photoinduced change in the charge order pattern in the quarter filled Organic Conductor edo ttf 2pf6 with a strong electron phonon interaction
Physical Review Letters, 2008Co-Authors: Ken Onda, Hideki Yamochi, Yoshiaki Nakano, Sho Ogihara, Kenji Yonemitsu, Nobuya Maeshima, T Ishikawa, Y Okimoto, Xiangfeng Shao, Gunzi SaitoAbstract:The quasistable state in the photoinduced phase transition for the quasi-one-dimensional quarter-filled Organic Conductor (EDO-TTF) 2 PF 6 has been examined by ultrafast reflective measurements and time-dependent model calculations incorporating both electron-electron and electron-phonon interactions. The transient optical conductivity spectrum over a wide probe photon-energy range revealed that photoexcitation induced a new type of charge-disproportionate state. Additionally, coherent and incoherent oscillations dependent on probe photon energies were found, as predicted by the calculation.
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photoinduced change in the charge order pattern in the quarter filled Organic Conductor edo ttf 2pf6 with a strong electron phonon interaction
Physical Review Letters, 2008Co-Authors: Ken Onda, Hideki Yamochi, Yoshiaki Nakano, Sho Ogihara, Kenji Yonemitsu, Nobuya Maeshima, T Ishikawa, Y Okimoto, Xiangfeng Shao, Gunzi SaitoAbstract:The quasistable state in the photoinduced phase transition for the quasi-one-dimensional quarter-filled Organic Conductor $(\mathrm{EDO}\mathrm{\text{\ensuremath{-}}}\mathrm{TTF}{)}_{2}{\mathrm{PF}}_{6}$ has been examined by ultrafast reflective measurements and time-dependent model calculations incorporating both electron-electron and electron-phonon interactions. The transient optical conductivity spectrum over a wide probe photon-energy range revealed that photoexcitation induced a new type of charge-disproportionate state. Additionally, coherent and incoherent oscillations dependent on probe photon energies were found, as predicted by the calculation.
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the photo induced phase and coherent phonon in the Organic Conductor edo ttf 2pf6
Journal of Physics: Condensed Matter, 2008Co-Authors: Hideki Yamochi, Gunzi Saito, Ken Onda, Sho Ogihara, T Ishikawa, Y Okimoto, Xiangfeng Shao, Shinya KoshiharaAbstract:We have investigated the nature of the photo-induced state and coherent phonon in the conducting charge transfer complex (EDO-TTF)2PF6 by measuring the ultrafast reflectivity change over a wide photon energy range from 0.069 eV (18 µm) to 2.1 eV (580 nm). The photo-induced spectra just after photo-excitation indicate that the photo-induced phase is similar to but clearly different from that in a thermally induced metal phase though they are the same for general photo-induced phase transition. The temporal profiles at each probe photon energy are accompanied by extraordinarily large amplitude oscillation originating from coherent phonon generation. The period of the coherent phonon depends discretely on the probe photon energy, while the generation efficiency of both the photo-induced phase and coherent photon reaches a maximum when the peak top of a charge transfer band is excited. These results are probably attributable to the strong electron–vibration coupling in this complex.
Kazuya Miyagawa - One of the best experts on this subject based on the ideXlab platform.
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disorder unveils mott quantum criticality behind a first order transition in the quasi two dimensional Organic Conductor κ et 2 cu n cn 2 cl
Physical Review B, 2019Co-Authors: Mizuki Urai, Kazuya Miyagawa, Takahiko Sasaki, Tetsuya Furukawa, Yasuhide Seki, Hiromi Taniguchi, Kazushi KanodaAbstract:We show the significant impact of weak disorder on the Mott transition by investigating electronic transport in a systematically x-ray-irradiated layered Organic Conductor under continuous pressure control. The critical end point of the first-order Mott transition is dramatically suppressed by such weak disorder that causes only a minor reduction in the transition temperature of disorder-sensitive nodal superconductivity. Instead, quantum critical scaling of resistance holds at lower temperatures and Fermi-liquid coherence temperature on the metallic side is lowered. Introducing disorder unveils the interaction-induced quantum criticality hidden behind the first-order transition.
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Observation of an anisotropic Dirac cone reshaping and ferrimagnetic spin polarization in an Organic Conductor
Nature Communications, 2016Co-Authors: Michihiro Hirata, Masafumi Tamura, Kazuya Miyagawa, Akito Kobayashi, Kyohei Ishikawa, Claude Berthier, Denis Basko, Genki Matsuno, Kazushi KanodaAbstract:The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping. In less symmetric Dirac materials possessing anisotropic cones with tilted axes, the Coulomb interaction can provide still more exotic phenomena which have not been experimentally unveiled yet. Here, using site-selective nuclear magnetic resonance, we find a non-uniform cone reshaping accompanied by a bandwidth reduction and an emergent ferrimagnetism in tilted Dirac cones that appear on the verge of charge ordering in an Organic compound. Our theoretical analyses based on the renormalization-group approach and the Hubbard model show that these observations are the direct consequences of the long-range and short-range parts of the Coulomb interaction, respectively. The cone reshaping and the bandwidth renormalization, as well as the novel magnetism revealed here, can be ubiquitous and vital for many Dirac materials.
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charge cluster glass in an Organic Conductor
Nature Physics, 2013Co-Authors: Fumitaka Kagawa, Taku J Sato, Kazuya Miyagawa, Kazushi Kanoda, Yoshinori Tokura, Kensuke Kobayashi, Reiji Kumai, Youichi MurakamiAbstract:Geometrically frustrated spin-systems do not order magnetically even at absolute zero, forming instead a spin liquid or a glassy state. An Organic Conductor in which the charges, rather than spins, are frustrated now shows a similar absence of long-range order, resulting in a charge-cluster glass at low temperature.
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13 c nmr study on the charge disproportionated conducting state in the quasi two dimensional Organic Conductor α bedt ttf 2 i 3
Physical Review B, 2011Co-Authors: Michihiro Hirata, Kazushi Kanoda, Kazuya Miyagawa, Kyohei Ishikawa, Masafumi TamuraAbstract:The conducting state of the quasi-two-dimensional Organic Conductor $\ensuremath{\alpha}$-(BEDT-TTF)${}_{2}$I${}_{3}$ at ambient pressure is investigated with ${}^{13}$C NMR measurements, which separate the local electronic states at three nonequivalent molecular sites (A, B, and C). The spin susceptibility and electron correlation effect are revealed in a locally resolved manner. While there is no remarkable site dependence around room temperature, the local spin susceptibility gradually disproportionates among the nonequivalent sites with decreasing temperature. The disproportionation ratio yields 5:4:6 for A:B:C molecules at 140 K. Distinct site and temperature dependences are also observed in the Korringa ratio ${\mathcal{K}}_{i}\ensuremath{\propto}{(1/{T}_{1}T)}_{i}{K}_{i}^{\ensuremath{-}2}$ ($i$ = A, B, and C), which is a measure of the strength and the type of electron correlations. The values of ${\mathcal{K}}_{i}$ point to sizable antiferromagnetic spin correlation. We argue the present results in terms of the theoretical prediction of the peculiar site-specific reciprocal-space ($\mathbit{k}$-space) anisotropy on the tilted Dirac cone, and discuss the $\mathbit{k}$-dependent profiles of the spin susceptibility and electron correlation on the cone.
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unconventional critical behaviour in a quasi two dimensional Organic Conductor
Nature, 2005Co-Authors: Fumitaka Kagawa, Kazuya Miyagawa, Kazushi KanodaAbstract:Changing the interactions between particles in an ensemble--by varying the temperature or pressure, for example--can lead to phase transitions whose critical behaviour depends on the collective nature of the many-body system. Despite the diversity of ingredients, which include atoms, molecules, electrons and their spins, the collective behaviour can be grouped into several families (called 'universality classes') represented by canonical spin models. One kind of transition, the Mott transition, occurs when the repulsive Coulomb interaction between electrons is increased, causing wave-like electrons to behave as particles. In two dimensions, the attractive behaviour responsible for the superconductivity in high-transition temperature copper oxide and Organic compounds appears near the Mott transition, but the universality class to which two-dimensional, repulsive electronic systems belongs remains unknown. Here we present an observation of the critical phenomena at the pressure-induced Mott transition in a quasi-two-dimensional Organic Conductor using conductance measurements as a probe. We find that the Mott transition in two dimensions is not consistent with known universality classes, as the observed collective behaviour has previously not been seen. This peculiarity must be involved in any emergent behaviour near the Mott transition in two dimensions.
Nobuo Ueno - One of the best experts on this subject based on the ideXlab platform.
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impact of an interface dipole layer on molecular level alignment at an Organic Conductor interface studied by ultraviolet photoemission spectroscopy
Physical Review B, 2004Co-Authors: Satoshi Kera, Yasufumi Yabuuchi, Hiroyuki Yamane, Hiroyuki Setoyama, Koji K. Okudaira, Antoine Kahn, Nobuo UenoAbstract:The effect of an interface dipole layer on the energy level alignment at Organic-Conductor interfaces is studied on a copper phthalocyanine (CuPc) monolayer/electric dipole layer/graphite system via ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy. An oriented monolayer of the OTi-phthalocyanine molecule, which has an electric dipole moment, is grown on graphite to yield a welldefined dipole layer with the vacuum side negatively charged. The CuPc monolayer is sequentially deposited on the dipole layer kept at 123 K. This weakly interacting system made of a very thin Organic layer on top of a very thin dipole layer is in thermodynamic equilibrium. The UPS data from the system grown with and without the interface dipole layer show that the binding energy of the highest occupied state of the CuPc monolayer decreases when the dipole layer is inserted. The binding energy shift is in excellent agreement with the increase in vacuum level energy of the graphite substrate upon deposition of the dipole layer. The results show that the Fermi level of the CuPc shifts toward the valence states when the interface dipole layer is inserted.
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impact of an interface dipole layer on molecular level alignment at an Organic Conductor interface studied by ultraviolet photoemission spectroscopy
Physical Review B, 2004Co-Authors: Satoshi Kera, Yasufumi Yabuuchi, Hiroyuki Yamane, Hiroyuki Setoyama, Koji K. Okudaira, Antoine Kahn, Nobuo UenoAbstract:The effect of an interface dipole layer on the energy level alignment at Organic-Conductor interfaces is studied on a copper phthalocyanine (CuPc) monolayer/electric dipole layer/graphite system via ultraviolet photoemission spectroscopy (UPS) and metastable atom electron spectroscopy. An oriented monolayer of the OTi-phthalocyanine molecule, which has an electric dipole moment, is grown on graphite to yield a well-defined dipole layer with the vacuum side negatively charged. The CuPc monolayer is sequentially deposited on the dipole layer kept at $123\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This weakly interacting system made of a very thin Organic layer on top of a very thin dipole layer is in thermodynamic equilibrium. The UPS data from the system grown with and without the interface dipole layer show that the binding energy of the highest occupied state of the CuPc monolayer decreases when the dipole layer is inserted. The binding energy shift is in excellent agreement with the increase in vacuum level energy of the graphite substrate upon deposition of the dipole layer. The results show that the Fermi level of the CuPc shifts toward the valence states when the interface dipole layer is inserted.