## YOSHIOKA HideoFaculty Division of Natural Sciences Research Group of Physics Professor |

Last Updated :2021/06/02

- Natural sciences, Magnetism, superconductivity, and strongly correlated systems
- Natural sciences, Semiconductors, optical and atomic physics

- - 1993, The University of Tokyo, 理学系研究科, 物理学, Japan
- - 1993, The University of Tokyo, Graduate School, Division of Science
- - 1988, Nagoya University, School of Science, 物理, Japan
- - 1988, Nagoya University, Faculty of Science

Transport Properties of Zigzag Ribbons Composed of Two-Dimensional Quantum Spin Hall Insulators with a Single Magnetic Impurity

Apr. 2020, Journal of the Physical Society of Japan, 89 (4), 043702Scientific journal

Phase Competition, Solitons, and Domain Walls in Neutral-Ionic Transition Systems

Phase competition and excitations in the one-dimensional neutral-ionic transition systems are theoretically studied comprehensively. From the semiclassical treatment of the bosonized Hamiltonian, we examine the competition among the neutral (N), ferroelectric-ionic (I-ferro), and paraelectric-ionic (I-para) states. The phase transitions between them can become first-order when the fluctuation-induced higher-order commensurability potential is considered. In particular, the description of the first-order phase boundary between N and Iferro enables us to analyze N-I-ferro domain walls. Soliton excitations in the three phases are described explicitly and their formation energies are evaluated across the phase boundaries. The characters of the soliton and domain-wall excitations are classified in terms of the topological charge and spin. The relevance to the experimental observations in the molecular neutral-ionic transition systems is discussed. We ascribe the pressure-induced crossover in tetrathiafulvalene-p-chloranil (TTF-CA) at a high-temperature region to that from the N to the I-para state, and discuss its consequence., PHYSICAL SOC JAPAN, Oct. 2016, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 85 (10), 104705, doi;web_of_scienceScientific journal

Tomonaga-Luttinger liquid theory for metallic fullurene polymers

We investigate the low energy behavior of local density of states in metallic C-60 polymers theoretically. The multichannel bosonization method is applied to electronic band structures evaluated from first-principles calculation, by which the effects of electronic correlation and nanoscale corrugation in the atomic configuration are fully taken into account. We obtain a closed-form expression for the power-law anomalies in the local density of states, which successfully describes the experimental observation on the C-60 polymers in a quantitative manner. An important implication from the closed- form solution is the existence of an experimentally unobserved crossover at nearly a hundred milli-electron volts, beyond which the power-law exponent of the C-60 polymers should change significantly., AMER PHYSICAL SOC, Apr. 2016, PHYSICAL REVIEW B, 93 (16), 165431, doi;web_of_scienceScientific journal

16aAG-13 Development of method for introducing lattice strain to graphene on BN

The Physical Society of Japan (JPS), Sep. 2015, 日本物理学会講演概要集 第70巻 第2号 2015年秋季大会, 70 (2), 1019Symposium

Enhancement of charge ordering by the zeeman effect in one-dimensional molecular conductors

The effects of an external magnetic field on the charge-ordered state are investigated within the one-dimensional extended Hubbard model with a quarter-filled band. We find that the external magnetic field leads to a coexistent state with three order parameters, i.e., the charge ordering, the uniform, and the staggered magnetic moments. In addition, the amplitude of the charge ordering is shown to be enhanced by the magnetic field. © 2013 The Korean Physical Society., Aug. 2013, Journal of the Korean Physical Society, 63 (3), 383 - 386, doiScientific journal

Theoretical Studies on Phase Transitions in Quasi-One-Dimensional Molecular Conductors

A review is given for recent theoretical studies on phase transitions in quasi-one-dimensional molecular conductors with a quarter-filled band. By lowering temperature, charge transfer salts exhibit a variety of transitions accompanying symmetry breaking, such as charge ordering, lattice dimerization, antiferromagnetic transition, spin-Peierls distortion, and so on. Analyses on microscopic quasi-one-dimensional models provide their systematic understandings, by the complementary use of different analytical and numerical techniques; they can reproduce finite-temperature phase transitions, whose results can be directly compared with experiments and give feedbacks to material design., MDPI AG, Sep. 2012, CRYSTALS, 2 (3), 996 - 1016, doi;web_of_scienceObservation of Riemannian geometric effects on electronic states

Einstein first applied Riemannian geometry to develop the general theory of relativity almost one hundred years ago and succeeded in understanding astronomical-scale phenomena such as the straining of time-space by a gravitational field. Whether or not Riemannian space affects the electronic properties of condensed matters on a much smaller scale is of great interest. Although Riemannian geometry has been applied to quantum mechanics since the 1950s, nobody has yet answered this question, because the electronic properties of materials with Riemannian geometry have not been examined experimentally. We report here the first observation of Riemannian geometrical effects on the electronic properties of materials such as Tomononaga-Luttinger liquids, which were previously theoretically predicted by our group. We present in situ high-resolution ultraviolet photoemission spectra of a one-dimensional metallic C-60 polymer with an uneven periodic peanut-shaped structure. Copyright (C) EPLA, 2012, EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY, Apr. 2012, EPL, 98 (2), 27001, doi;web_of_scienceScientific journal

Formation of graphene with one dimensional local strain and transport measurement

The Physical Society of Japan (JPS), Mar. 2012, Meeting abstracts of the Physical Society of Japan, 67 (1), 885Scientific journal

One-Dimensional Uneven Peanut-Shaped C-60 Polymer: A Quantum Electronic System in Riemannian Space

When a C-60 film is irradiated with a 3 kV electron-beam in an ultrahigh vacuum (base pressure: 10(-7) Pa), C-60 molecules are coalesced to form a one-dimensional (1D) uneven peanut-shaped C-60 polymer. From a topological viewpoint, since the polymer has both positive and negative Gaussian curvatures, it can be regarded as a new allotrope of nanocarbons different from graphene, fullerenes, and nanotubes. We will present our recent results of the electronic, optical, and electron-transport properties of the 1D uneven peanut-shaped C-60 polymer and discuss its novel electronic properties on the basis of quantum mechanics in Riemannian space., TAYLOR & FRANCIS INC, 2012, FULLERENES NANOTUBES AND CARBON NANOSTRUCTURES, 20 (1), 1 - 16, doi;web_of_scienceScientific journal

Collapse of Charge Ordering Due to Disorder in Quasi One-Dimensional Electron Systems

Effects of disorder on charge ordering ( CO) is investigated for one-dimensional (1D) and quasi 1D extended Hubbard model with infinite on-site repulsion at quarter filling. Only the forward scattering due to disorder is taken into account. In the 1D model, the resistivity due to Umklapp scattering that is an origin of CO is shown to be suppressed by the forward scattering. In addition, we obtain that the CO transition temperature T-CO for quasi 1D model becomes smaller with increasing strength of the forward scattering., IOP PUBLISHING LTD, 2012, 26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, 400, 032125, doi;web_of_scienceInternational conference proceedings

Supercurrent through Graphene: Effects of Vanishing Density of States

The critical current through superconductor-graphene-superconductor Josephson junction has been studied theoretically in terms of tunnel Hamiltonian approximation. In this paper we especially focus on the effects of vanishing density of state at Fermi level in monolayer graphene. We discuss a characteristic suppression of critical current at low temperature., IOP PUBLISHING LTD, 2012, 26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, 400, 022024, doi;web_of_scienceInternational conference proceedings

Effects of Hopping Modulation at the Edges on Transport Properties of Zigzag Graphene Nanoribbon Attached to Two Normal Metals

Transport properties of the junction composed of graphene nanoribbon with zigzag shaped edges attached to two normal metals are theoretically investigated. In order to clarify roles of zigzag edges on the transport properties, we consider the system where the hopping at the zigzag edges are weaker than the other bond. The results are compared with the case without modulation studied previously., IOP PUBLISHING LTD, 2012, 26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5, 400, 042077, doi;web_of_scienceInternational conference proceedings

Incommensurate Antiferromagnetic Insulating State in (MDT-TS)(AuI2)(x)

We theoretically study the metal-insulator transition in a molecular conductor (MDT-TS)(AuI2)(x) composed with an incommensurate ratio (x = 0.441), where the conduction band originated from the HOMO of donor MDT-TS molecules is incommensurately filled. We consider a two-dimensional Hubbard model taking account of anisotropic transfer integrals in the donor layer, under a periodic potential due to the anions (AuI2)(-) which mismatches the donor lattice period, and investigate the ground state within mean-field approximation. An antiferromagnetic insulating state with induced charge disproportionation is obtained in the large U and delta region; the symmetry in the charge sector is unchanged from the paramagnetic metallic state realized at small U and delta, therefore this state corresponds to the incommensurate Mott insulating state predicted previously [H. Yoshioka et al.: J. Phys. Soc. Jpn. 74 (2005) 1922] based on a simplified one-dimensional model., PHYSICAL SOC JAPAN, Dec. 2011, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 80 (12), 123702, doi;web_of_scienceScientific journal

Electronic spectral shift of oxygen-filled (6,6) carbon nanotubes

Electronic state modulation of armchair (6,6) carbon nanotubes filled with a linear assembly of oxygen molecules is addressed theoretically. Ferromagnetic ordering of encapsulated oxygen produces a magnetic field with cylindrical symmetry, which deviates the electron's eigenenergies from those prior to the oxygen absorption. An intriguing spectral gap arises near the Fermi energy, at which the gap formation is allowed only when the tube length equals to a multiple of three in units of carbon hexagon. A possible means to detect the selective gap formation is discussed. (C) 2011 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, Sep. 2011, CHEMICAL PHYSICS LETTERS, 513 (4-6), 224 - 228, doi;web_of_scienceScientific journal

Density of states anomalies in multichannel quantum wires

We reformulate the Tomonaga-Luttinger liquid theory for quasi-one-dimensional Fermion systems with many subbands across the Fermi energy. Our theory enables us to obtain a rigorous expression of the local density of states (LDOS) for general multichannel quantum wires, describing how the power-law anomalies of the LDOS depend on inter- and intra-subbands couplings as well as the Fermi velocity of each band. The resulting formula for the exponents is valid in the cases of both bulk contact and edge contact, and thus plays a fundamental role in the physical properties of multicomponent Tomonaga-Luttinger liquid systems., AMER PHYSICAL SOC, Aug. 2011, PHYSICAL REVIEW B, 84 (7), 075443, doi;web_of_scienceScientific journal

Manipulating the Tomonaga-Luttinger exponent by electric field modulation

We establish a theoretical framework for artificial control of the power-law singularities in Tomonaga-Luttinger liquid states. The exponent governing the power-law behaviors is found to increase significantly with an increase in the amplitude of spatially periodic electrostatic field applied to the system. This field-induced shift in the exponent indicates the tunability of the transport properties of quasi-one-dimensional electron systems., SPRINGER, Dec. 2010, EUROPEAN PHYSICAL JOURNAL B, 78 (4), 481 - 488, doi;web_of_scienceScientific journal

Theoretical study of superconducting proximity effect in single and multi-layered graphene

Theoretical analysis of superconducting current in graphite thin films (or graphene) in proximity to superconductors is presented, especially paying attention to the band structure. We derive the general formula to calculate the free energy of the superconductor-graphite film-superconductor junction, which enable us to calculate the critical current of the junction. We introduce two models for the band structures: (1) Fermi point type (characteristic to monolayer case) and (2) zero-gap semiconductor type (characteristic to bilayer case). Then we calculate the superconducting critical current as a function of junction length and temperature. (C) 2009 Published by Elsevier B.V., ELSEVIER SCIENCE BV, Dec. 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, S846 - S847, doi;web_of_scienceScientific journal

Finite-Temperature Properties across the Charge Ordering Transition-Combined Bosonization, Renormalization Group, and Numerical Methods-

We theoretically describe the charge ordering (CO) metal-insulator transition based on a quasi-one-dimensional extended Hubbard model, and investigate the finite temperature (T) properties across the transition temperature, T-CO. In order to calculate T dependence of physical quantities such as the spin susceptibility and the electrical resistivity, both above and below T-CO, a theoretical scheme is developed which combines analytical methods with numerical calculations. We take advantage of the renormalization group equations derived from the effective bosonized Hamiltonian, where Lanczos exact diagonalization data are chosen as initial parameters, while the CO order parameter at finite-T is determined by quantum Monte Carlo simulations. The results show that the spin susceptibility does not show a steep singularity at T-CO, and it slightly increases compared to the case without CO because of the suppression of the spin velocity. In contrast, the resistivity exhibits a sudden increase at T-CO, below which a characteristic T dependence is observed. We also compare our results with experiments on molecular conductors as well as transition metal oxides showing CO., PHYSICAL SOC JAPAN, Sep. 2010, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 79 (9), 094714, doi;web_of_scienceScientific journal

23pXB-2 Theory of Superconducting Proximity Effect in Graphene II

The Physical Society of Japan (JPS), Aug. 2010, Meeting abstracts of the Physical Society of Japan, 65 (2), 743Scientific journal

Anomalous Interaction Dependence in Magnetism of Graphene Nanoribbons with Zigzag Edges

The properties in magnetic ordered states of graphene nanoribbons with zigzag-shaped edges are investigated by applying mean-field approximation to the Hubbard model with the on-site repulsion U. We observe that magnetic moments and critical temperature show anomalous power-law dependences as a function of U; the actual values of the power are determined by only the width of the ribbons. Such singular behaviours are found to be due to the localized nature of the electronic states close to the Fermi energy., PHYSICAL SOC JAPAN, Aug. 2010, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 79 (8), 084708, doi;web_of_scienceScientific journal

21aGS-5 Superconducting proximity effect in few-layer graphene

The Physical Society of Japan (JPS), Mar. 2010, Meeting abstracts of the Physical Society of Japan, 65 (1), 872Scientific journal

Transport properties of normal metal-graphene nanoribbon-normal metal junctions

Transport properties are investigated theoretically for the junctions consisting of two normal metals and a graphene nanoribbon which has zigzag shaped edges with the electron hopping weaker than that in the other region. We find that the conductance of the present model has the same asymptotic behavior for N(L) >> 1 as that with the spatially uniform hopping in the N(L) >= 3 case, where N(L) and N are integers corresponding to length and width, respectively. The result seems to indicate that the zigzag edges do not contribute to the transport properties in the case with N(L) >> 1. (C) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, Feb. 2010, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 42 (4), 722 - 725, doi;web_of_scienceScientific journal

Curvature effects on collective excitations in dumbbell-shaped hollow nanotubes

We investigate surface-curvature induced alteration in the Tomonaga-Luttinger liquid (TLL) states of a one-dimensional (1D) deformed hollow nanotube with a dumbbell-shape. Periodic variation of the surface curvature along the axial direction is found to enhance the TLL exponent significantly, which is attributed to an effective potential field that acts low-energy electrons moving on the curved surface. The present results accounts for the experimental observation of the TLL properties of 1D metallic peanut-shaped fullerene polymers whose enveloping surface is assumed to be a dumbbell-shaped hollow tube. (c) 2009 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, Feb. 2010, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 42 (4), 1151 - 1154, doi;web_of_scienceScientific journal

Superconducting proximity effect in graphene nanostructures

The superconducting proximity effect is studied theoretically for graphene(G)-superconductor(S) hybrid structures. Especially S-G-S junction is considered and the critical current is argued focusing on its temperature and junction-length dependences. The free energy of the total system is calculated by use of the tunneling approximation and the critical current is estimated from it. It is reported that the critical current can oscillate as a function of temperature and junction-length in bi-layer junctions. Some detailed comparison with ordinary S-normal metal-S junctions is also given and both monolayer and bilayer junctions show some characteristic deviations., IOP PUBLISHING LTD, 2010, INTERNATIONAL CONFERENCE ON THEORETICAL PHYSICS DUBNA-NANO 2010, 248, 012002, doi;web_of_scienceInternational conference proceedings

Theoretical Study on Transport Properties of Normal Metal-Zigzag Graphene Nanoribbon-Normal Metal Junctions

We investigate transport properties of the junctions in which the graphene nanoribbon with the zigzag shaped edges consisting of the N legs is sandwiched by the two normal metals by means of recursive Green's function method. The conductance and the transmission probabilities are found to have the remarkable properties depending on the parity of N. The singular behaviors close to E = 0 with E being the Fermi energy are demonstrated. The channel filtering is shown to occur in the case with N = even., PHYSICAL SOC JAPAN, Dec. 2009, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 78 (12), 123701, doi;web_of_scienceScientific journal

26pYE-9 Anomalous behavior of proximity-induced superconducting transition in multilayer graphene under gate-electric field

The Physical Society of Japan (JPS), Aug. 2009, Meeting abstracts of the Physical Society of Japan, 64 (2), 765Scientific journal

Geometry-driven shift in the Tomonaga-Luttinger exponent of deformed cylinders

We demonstrate the effects of geometric perturbation on the Tomonaga-Luttinger liquid (TLL) states in a long, thin, and hollow cylinder whose radius varies periodically. The variation in the surface curvature inherent to the system gives rise to a significant increase in the power-law exponent of the single- particle density of states. The increase in the TLL exponent is caused by a curvature-induced potential that attracts low-energy electrons to region that has large curvature. © 2009 The American Physical Society., 01 May 2009, Physical Review B - Condensed Matter and Materials Physics, 79 (20), doiScientific journal

Geometry-driven shift in the Tomonaga-Luttinger exponent of deformed cylinders

We demonstrate the effects of geometric perturbation on the Tomonaga-Luttinger liquid (TLL) states in a long, thin, and hollow cylinder whose radius varies periodically. The variation in the surface curvature inherent to the system gives rise to a significant increase in the power-law exponent of the single- particle density of states. The increase in the TLL exponent is caused by a curvature-induced potential that attracts low-energy electrons to region that has large curvature., AMER PHYSICAL SOC, May 2009, PHYSICAL REVIEW B, 79 (20), 201401, doi;web_of_scienceScientific journal

Properties of nano-graphite ribbons with zigzag edges - Difference between odd and even legs

Persistent currents and transport properties are investigated for the nano-graphite ribbons with zigzag shaped edges with paying attention to system length L dependence. It is found that both the persistent current in the isolated ring and the conductance of the system connected to the perfect leads show the remarkable L dependences. In addition, the dependences for the systems with odd legs and those with even legs are different from each other. On the persistent current, the amplitude for the cases with odd legs shows power-low behavior as L(-N) with N being the number of legs, whereas the maximum of it decreases exponentially for the cases with even legs. The conductance per one spin normalized by e(2)/h behaves as follows. In the even legs cases, it decays as L(-2), whereas it reaches to unity for L -> infinity in the odd legs cases. Thus, the material is shown to have a remarkable property that there is the qualitative difference between the systems with odd legs and those with even legs even in the absence of the electron-electron interaction., IOP PUBLISHING LTD, 2009, 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 2, 150, 022105, doi;web_of_scienceInternational conference proceedings

グラフェンにおける超伝導近接効果の理論(不均一超伝導超流動状態と量子物理,研究会報告)

Bussei Kenkyu, Dec. 2008, Bussei Kenkyu, 91 (3), 241Scientific journal

Superconducting proximity effect through graphene and graphite films

We discuss the superconducting proximity effect in graphite films (or graphene) by studying the critical current through superconductor-graphite film (or graphene)superconductor Josephson junction. The two leads are assumed to be conventional s-wave superconductors. We especially pay attention to the dispersions of electrons in graphite films: because of the delicate band structure of graphite, the electron dispersion in the film, which undergoes the effects of various external factors such as leads, gate electrodes and sample inhomogeneities, can show a wide variety. We introduce several models for electron dispersion near Fermi energy: 1) graphene-like Fermi points, 2) semi-metal, and 3) semiconducting gap. The superconducting critical current I, through the junction is usually expressed as I-c proportional to exp{-d/xi(T)}, where d is the distance between two leads and xi(T) is the proximity length. We show that the temperature dependence of (T) is largely affected by the band structure of the graphite film and by examining this dependence some insight into the electronic properties of the graphite film can be obtained., IOP PUBLISHING LTD, 2008, INTERNATIONAL SYMPOSIUM ON ADVANCED NANODEVICES AND NANOTECHNOLOGY, 109, 012014, doi;web_of_scienceInternational conference proceedings

Mott insulating state in incommensurate molecular conductors

2008, Journal of Physics: Conference Series, 132, 012018Charge-ordered state versus Dimer-Mott insulator at finite temperatures

We theoretically investigate the competition between charge-ordered state and Mott insulating state at finite temperatures in quarter-filled quasi-one-dimensional electron systems, by studying dimerized extended Hubbard chains with interchain Coulomb interactions. In order to take into account onedimensional fluctuations properly, we apply the bosonization method to an effective model obtained by the interchain mean-field approximation. The results show that lattice dimerization, especially in the critical region, and frustration in the interchain Coulomb interactions reduce the charge-ordering phase transition temperature and enlarge the dimer-Mott insulating phase. We also derive a general formula of the Knight shift in the charge-ordered phase and its implication to experiments is discussed., PHYSICAL SOC JAPAN, Oct. 2007, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 76 (10), 103701, doi;web_of_scienceScientific journal

Knight shift in the charge ordered states of the one-dimensional electron systems at 1/4 filling

Knight shift in the pure charge ordered states is calculated for the one-dimensional extended Hubbard model at quarter filling. The cases of charge ordered state with a 2-fold periodicity and with a 4-fold one are investigated based on the mean-field theory. It is shown that splitting of the Knight shift observed below the transition temperature reflects not the periodicity enlarged by the charge ordering but the charge disproportionation. (c) 2006 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, Mar. 2007, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 310 (2), E332 - E334, doi;web_of_scienceScientific journal

Finite-temperature charge-ordering transition and fluctuation effects in quasi one-dimensional electron systems at quarter filling

Finite-temperature charge-ordering phase transition in quasi one-dimensional (ID) molecular conductors is investigated theoretically, based on a quasi I D extended Hubbard model at quarter filling with interchain Coulomb repulsion V-perpendicular to. The interchain term is treated within a mean-field approximation, and the ID fluctuations in the chains are fully taken into account by the bosonization theory. Three regions are found depending on the appearance of the charge-ordered state at a finite temperature when V-perpendicular to is introduced: (i) a weak-coupling region where the system transforms from a metal to a charge-ordered insulator with a finite transition temperature at a finite critical value of V-perpendicular to, (ii) an intermediate region where this transition occurs by infinitesimal V-perpendicular to due to the stability of the inherent ID fluctuation, and (iii) a strong-coupling region where the charge ordered state is already realized in a purely 1D case, of which the transition temperature becomes finite with infinitesimal V-perpendicular to. An analytical formula for the V-perpendicular to dependence of the transition temperature is derived for each region., PHYSICAL SOC JAPAN, Jun. 2006, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 75 (6), 063706, doi;web_of_scienceScientific journal

Theoretical aspects of charge ordering in molecular conductors

Theoretical studies on charge ordering phenomena in quarter-filled molecular (organic) conductors are reviewed. Extended Hubbard models including not only the on-site but also the inter-site Coulomb repulsion are constructed in a straightforward way from the crystal structures, which serve for individual study on each material as well as for their systematic understandings. In general the inter-site Coulomb interaction stabilizes Wigner crystal-type charge ordered states, where the charge localizes in an arranged manner avoiding each other, and can drive the system insulating. The variety in the lattice structures, represented by anisotropic networks in not only the electron hopping but also in the inter-site Coulomb repulsion, brings about diverse problems in low-dimensional strongly correlated systems. Competitions and/or co-existences between the charge ordered state and other states are discussed, such as metal, superconductor, and the dimer-type Mott insulating state which is another typical insulating state in molecular conductors. Interplay with magnetism, e.g., antiferromagnetic state and spin gapped state is considered as well. Distinct situations are pointed out: influences of the coupling to the lattice degree of freedom and effects of geometrical frustration which exists in many molecular crystals. Some related topics, such as charge order in transition metal oxides and its role in new molecular conductors, are briefly remarked., PHYSICAL SOC JAPAN, May 2006, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 75 (5), 051009, doi;web_of_scienceKnight shift and nuclear spin relaxation rate in a charge-ordered state of the one-dimensional extended Hubbard model at quarter filling

We investigate Knight shift and nuclear spin relaxation rate in a charge-ordered state of the one-dimensional extended Hubbard model with a quarter-filled band by using RPA around the mean-field solution. It is shown that both quantities show splitting below the critical temperature of the charge order, as is experimentally observed. The relationships between the amount of the splitting in the both quantities and the charge disproportionation rate are discussed., PHYSICAL SOC JAPAN, Mar. 2006, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 75 (3), 034703, doi;web_of_scienceScientific journal

Theoretical study on knight shift and nuclear spin relaxation rate in the charge ordering state of the ID quarter-filled electron system

We study theoretically the Knight shift and the nuclear spin relaxation rate in the charge ordering (CO) state of the one-dimensional extended Hubbard model with a quarter-filled band. It is shown that the both quantities split into the two components below the critical temperature of CO, which is different from the half-filled case. The relationship between the amount of splitting in these quantities and the charge disproportionation rate is discussed., SPRINGER/PLENUM PUBLISHERS, Feb. 2006, JOURNAL OF LOW TEMPERATURE PHYSICS, 142 (3-4), 503 - 506, doi;web_of_scienceScientific journal

Incommensurate Mott insulator in one-dimensional electron systems close to quarter filling

The possibility of metal-insulator transition in molecular conductors has been studied for systems composed of donor molecules and fully ionized anions with an incommensurate ratio close to 2 : I based on the one-dimensional extended Hubbard model, where donor carriers are slightly deviated from quarter filling and under an incommensurate periodic potential from anions. By the renormalization group method, the interplay between commensurability energy on the donor lattice and that from the anion potential has been studied and it has been found that an "incommensurate Mott insulator" can be generated. This theoretical finding will qualitatively explain the appearance of the insulating state in a two-dimensional material with an incommensurate, PHYSICAL SOC JAPAN, Jul. 2005, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 74 (7), 1922 - 1925, doi;web_of_scienceScientific journal

Photoemission spectroscopy on single-wall carbon nanotubes

One-dimensional nature of single-wall carbon nanotubes (SWNTs) has been investigated by the photoemission spectroscopy on SWNT samples with different diameters. We successfully observe peak structures that arise from one-dimensional van Hove singularities. The spectral function and the intensity at the Fermi level both exhibit power-law behavior with almost identical exponents, which indicates that the metallic SWNTs are regarded as ideal one-dimensional systems. (C) 2004 Elsevier B.V. All rights reserved., ELSEVIER SCIENCE BV, Sep. 2004, PHYSICA B-CONDENSED MATTER, 351 (3-4), 259 - 261, doi;web_of_scienceScientific journal

Charge ordering and Knight shift in one-dimensional electron systems nearly half-filling

We investigate Knight shift in the charge ordered state of the one-dimensional electron system nearly half-filling. It is shown that the splitting of Knight shift occurs below the critical temperature of charge ordering. This finding is different from the case of just half-filling, where the splitting does not occur even in the charge ordered state. In addition. we find the simple relations among the difference between the shift in the charge rich site and that in the poor site and the mount of the charge transfer., E D P SCIENCES, Apr. 2004, JOURNAL DE PHYSIQUE IV, 114, 159 - 161, doi;web_of_scienceScientific journal

Electronic structure of single-wall carbon nanotubes and peapods; Photoemission study

Electronic structure of single-wall carbon nanotubes was investigated by photoemission spectroscopy. Oscillations in electronic density of states due to one-dimensional van Hove singularities were clearly observed near the Fermi level, which can be well reproduced by simple tight-binding calculation with assumptions a broadening and an energy shift probably due to a charge transfer from the metal substrate. Furthermore, in the vicinity of the Fermi level, two kinds of typical power-law dependences were observed that can be regarded as evidence of Tomonaga-Luttinger liquid states. Both exponents show very similar values 0.46 and 0.48 good agreement with theoretical prediction. Results on fullerene peapod system are also discussed., AMER INST PHYSICS, 2004, ELECTRONIC PROPERTIES OF SYNTHETIC NANOSTRUCTURES, 723, 222 - 226, web_of_scienceInternational conference proceedings

Direct observation of Tomonaga-Luttinger-liquid state in carbon nanotubes at low temperatures

The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga-Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons(1-3). Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states(4-6). Indeed, the results of transport measurements on metal - SWNT and SWNT - SWNT junctions have been attributed(7-9) to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations(10). Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the pi-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour ( with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs., NATURE PUBLISHING GROUP, Dec. 2003, NATURE, 426 (6966), 540 - 544, doi;web_of_scienceScientific journal

Spin excitation in nano-graphite ribbons with zigzag edges

Spin excitation in a nano-graphite ribbon with zigzag edges is investigated theoretically. Due to the strongly localized nature of the states near the Fermi energy, the effective Hamiltonian for the low-energy physics is given by the Heisenberg Hamiltonian with the nearest neighbor exchange coupling. The action corresponding to the effective Hamiltonian is mapped to that of the O(3) nonlinear sigma model. It is shown that the spin excitation has a gap when the number of the zigzag lines is even, whereas the excitation becomes gapless in the case of an odd number of zigzag lines., PHYSICAL SOC JAPAN, Sep. 2003, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 72 (9), 2145 - 2148, doi;web_of_scienceScientific journal

Tomonaga-Luttinger-liquid behavior in conducting carbon nanotubes with open ends

We discuss the local density of states (LDOS) of the semi-infinite conducting carbon nanombe based on the bosonization theory of one-dimensional electron systems with open boundaries. The dependences of the spatially slowly varying component of the LDOS on location, energy and temperature are investigated. (C) 2003 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, May 2003, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 18 (1-3), 212 - 213, doi;web_of_scienceScientific journal

Excitations in the charge ordered state of one-dimensional extended Hubbard model at half-filling

We investigate excitation spectra in the charge ordered state of the one-dimensional extended Hubbard model at half-filling with taking account of fluctuations around the mean-field solution. The imaginary parts of the dynamical susceptibilities, the dispersion relations and the weights of the collective modes are discussed., ELSEVIER SCIENCE SA, Apr. 2003, SYNTHETIC METALS, 135 (1-3), 551 - 552, doi;web_of_scienceScientific journal

Commensurate-incommensurate transition in a one-dimensional dimerized electron system close to quarter-filling

We investigate electronic states upon doping (i.e., by varying the chemical potential) for a quarter-filled one-dimensional electron system with a dimerization, on-site and nearest-neighbor repulsive interaction. By applying the renormalization group method to the bosonized Hamiltonian, the metal-insulator transition followed by commensurate-incommensurate transition is obtained for Mott insulating region as well as charge ordered insulating regime. We discuss the phase diagram on the plane of the chemical potential and the interaction. (C) 2002 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE SA, Mar. 2003, SYNTHETIC METALS, 133, 49 - 50, doi;web_of_scienceScientific journal

Valence-band photoemission study of single-wall carbon nanotubes

We have performed the valence-band photoemission spectroscopy on single-wall carbon nanotubes. Characteristic peak structures originated from one-dimensional van Hove singularities have been successfully observed. The peak structures are well reproduced by the calculation based on the tight-binding model taking into account a diameter distribution of nanotubes., AMER INST PHYSICS, 2003, MOLECULAR NANOSTRUCTURES, 685, 139 - 142, doi;web_of_scienceInternational conference proceedings

Tomonaga-Luttinger-liquid theory of metallic carbon nanotubes with open boundaries

Tomonaga-Luttinger-liquid theory is formulated for metallic carbon nanotubes with open boundaries. Both cases of single- and multi-wall nanotubes are discussed. Based on this theory, spatial variation of the charge density from an edge is investigated with taking account of the shift of the chemical potential which expresses the carrier injection to the nanotube. The charge density has the spatially independent part and the oscillatory component. Roles of Coulomb interaction on the amplitude of the oscillation, the wavenumbers of it and the uniform component of the charge. density are clarified., PHYSICAL SOC JAPAN, Oct. 2002, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (10), 2512 - 2519, doi;web_of_scienceScientific journal

Magnetic fluctuations in a charge-ordered state of the one-dimensional extended Hubbard model with a half-filled band

Magnetic properties in a charge-ordered state are examined for the extended Hubbard model at half-filling. Magnetic excitations, magnetic susceptibilities and a nuclear spin relaxation rate are calculated with taking account of fluctuations around the mean-field solution. The relevance of the present results to the observation in the 1:1 organic conductors, (TTM-TTP)I-3, is discussed., PHYSICAL SOC JAPAN, Aug. 2002, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 71 (8), 1812 - 1815, doi;web_of_scienceScientific journal

NMR relaxation rate in metallic carbon nanotubes

NMR relaxation rate, T-1(-1), of the metallic carbon nanotube is discussed based on Tomonaga-Luttinger-liquid theory. It is found that the Coulomb interaction leads to increase of (T1T)(-1) by a power law with decreasing temperature, T. The dependence on temperature of (T1T)(-1) in the multi-wall nanotube (MWNT) is shown to be strongly suppressed by existence of the metallic shells in the MWNTs. (C) 2002 Elsevier Science Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, Jun. 2002, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 63 (6-8), 1281 - 1284, doi;web_of_scienceScientific journal

Oscillator strength of metallic carbon nanotubes

Based on the tight binding method with a hopping integral between the nearest-neighbor atoms, an oscillator strength integral (infinity)(0) d omega Re sigma(omega) is discussed for armchair and metallic zigzag carbon nanotubes. The formulae of the oscillator strength are derived for both types of nanotubes and are compared with the result obtained by a linear chain model. In addition, the doping dependence is investigated in the absence of the Coulomb interaction. It is shown that the oscillator strength of each carbon nanotube shows qualitatively the same doping dependence, hut the fine structure is different due to its own peculiar band structure. Some relations independent of the radius of the tube are derived; and a useful formula for determining the amount of doping is proposed., PHYSICAL SOC JAPAN, Jan. 2001, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 70 (1), 17 - 20, doi;web_of_scienceScientific journal

Effects of next-nearest-neighbor repulsion on one-dimensional quarter-filled electron systems

We examine effects of the next-nearest-neighbor repulsion on electronic states of a one-dimensional interacting electron system which consists of quarter-filled band and interactions of on-site and nearest-neighbor repulsion. We derive the effective Hamiltonian for the electrons around wave number +/-k(F) (K-F: Fermi wave number) and apply the renormalization group method to the bosonized Hamiltonian. It is shown that the next-nearest-neighbor repulsion makes 4k(F)-charge ordering unstable and suppresses the spin fluctuation. Further the excitation gaps and spin susceptibility are also evaluated., PHYSICAL SOC JAPAN, Mar. 2001, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 70 (3), 762 - 773, doi;web_of_scienceScientific journal

Crossover from quarter-filling to half-filling in a one-dimensional electron system with a dimerized and quarter-filled band

The interplay between quarter-filled and half-tilled umklapp scattering has been examined by applying the renormalization group method to a one-dimensional quarter-filled electron system with dimerization, on-site (U) and nearest-neighbor (V) repulsive interactions. The phase diagram on the U-V plane is obtained at absolute zero temperature where the Mott, insulator (the charge ordered insulator) is found for smaller (larger) V. By choosing the moderate parameter in the region of Mott insulator, it is shown that the resistivity exhibits a crossover from behavior of quarter-filling to that of half-filling with decreasing temperature., PHYSICAL SOC JAPAN, Jun. 2001, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 70 (6), 1460 - 1463, doi;web_of_scienceScientific journal

Two kinds of metallic states in carbon nanotubes - differences in transport properties

The differences between the metallic states with two valleys (2 nu) and with one valley (1 nu), both of which are realized in carbon nanotubes, are investigated through Tomonaga-Luttinger liquid behaviors in the transport properties due to the impurity potential. It is shown that the effects of Coulomb interaction are stronger in the 1 nu states than in the 2 nu states. The possibility of observation of the present results in multi wall carbon nanotubes is discussed. (C) 2000 Elsevier Science Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2001, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 62 (1-2), 413 - 417, doi;web_of_scienceScientific journal

Commensurability in one-dimensional electron systems at quarter-filling

We examine the role of commensurability in electronic states and excitations for a one-dimensional interacting electron system at quarter-filling with on-site (U), nearest-neighbor (V-1) and next-nearest-neighbor (V-2) repulsive interactions, By applying the renormalization group method to the bosonized model, it is shown that the next-nearest-neighbor repulsion stabilizes 2k(F) density waves and induces the excitation gap in spin fluctuation for V-2 > U/2, (C) 2000 Elsevier Science Ltd. All rights reserved., PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2001, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 62 (1-2), 419 - 422, doi;web_of_scienceScientific journal

Effects of a transverse electric field on charge-density waves

A transverse electric field (a field perpendicular to the quasi-one-dimensional conducting chains) applied to a charge-density wave (CDW) causes frustration in the ordered state and has similar effects to a magnetic field applied to a superconductor. We study the equilibrium states of CDW in the transverse electric field paying attention to this similarity. Corresponding to type-I and type-II superconductivity, two types of CDW are investigated. (C) 2000 Elsevier Science B.V, All rights reserved., ELSEVIER SCIENCE BV, Jul. 2000, PHYSICA B, 284, 1535 - 1536, web_of_scienceScientific journal

Correlation gap in one-dimensional quarter-filled electron system

Umklapp scattering in an one-dimensional quarter-filled electron system with both on-site U(> 0) and nearest-neighbor V(> 0) interactions is examined by applying the renormalization group method to the bosonized Hamiltonian. We calculate a correlation gap, which appears for V larger than a critical value. In such a case, the spin density wave (SDW) coexists with the charge disproportion with two-fold periodicity. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, Jul. 2000, PHYSICA B, 284, 1547 - 1548, web_of_scienceScientific journal

Effects of Coulomb interaction on resistivity of metallic carbon nanotubes with impurity potential

Transport properties of two kinds of metallic states, which have been found in single wall carbon nanotubes, are examined in the presence of impurity potential and long-range Coulomb interaction. It is shown that Coulomb interaction leads to the power-law dependence in the resistivity as a function of temperature, and modifies the power of frequency dependence of the optical conductivity at zero temperature, which is seen in high frequency. However, the powers are different between both the states. (C) 2000 Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, Jul. 2000, PHYSICA B, 284, 1756 - 1757, web_of_scienceScientific journal

Correlation effects in a one-dimensional quarter-filled electron system with repulsive interactions

A one-dimensional electron system at quarter-filling has been examined by applying the renormalization group method to a bosonized model with on-site (U) and nearest-neighbor (V) repulsive interactions. By evaluating both normal scattering and Umklapp scattering perturbatively, we obtain a phase diagram in which a metallic state with a 2k(F) spin density wave (k(F) is the Fermi wave number) mol-es into an insulating state with charge disproportionation of a 4k(F) charge density wave with an increase in both U and V. The effect of the next-nearest-neighbor repulsion is also discussed., PHYSICAL SOC JAPAN, Mar. 2000, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 69 (3), 651 - 654, doi;web_of_scienceTransport properties of disordered carbon nanotubes with long-range Coulomb interaction

Transport properties of disordered carbon nanotubes are investigated including long-range Coulomb interaction. The resistivity and optical conductivity are calculated by using the memory functional method. In addition, the effect of localization is taken into account by use of the renormalization-group analysis, and it is shown that the backward scattering of the intravalley and that of the intervalley cannot coexist in the localized regime. Differences between the transport properties for the metallic state with two valleys and those with one valley are discussed., AMER PHYSICAL SOC, Mar. 2000, PHYSICAL REVIEW B, 61 (11), 7316 - 7319, doi;web_of_scienceScientific journal

Correlated electrons in carbon nanotubes

Single-wall carbon nanotubes are almost ideal systems for the investigation of exotic many-body effects due to non-Fermi liquid behavior of interacting electrons in one dimension. Recent theoretical and experimental results are reviewed with a focus on electron correlations. Starting from a microscopic lattice model we derive an effective phase Hamiltonian for conducting single-wall nanotubes with arbitrary chirality. The parameters of the Hamiltonian show very weak dependence on the chiral angle, which makes the low-energy physics of conducting nanotubes universal. The temperature-dependent resistivity and frequency-dependent optical conductivity of nanotubes with impurities are evaluated within the Luttinger-like model. Localization effects are studied. In particular, we found that intra-valley and inter-valley electron scattering can not coexist at low energies. Low-energy properties of clean nanotubes are studied beyond the Luttinger liquid approximation. The strongest Mott-like electron instability occurs at half filling. In the Mott insulating phase electrons at different atomic sublattices form characteristic bound states. The energy gaps occur in all modes of elementary excitations and estimate at 0.01 - 0.1 eV. We finally discuss observability of the Mott insulating phase in transport experiments. The accent is made on the charge transfer from external electrodes which results in a deviation of the electron density from half-filling., SPRINGER-VERLAG BERLIN, 2000, LOW-DIMENSIONAL SYSTEMS, 544, 97 - 111, web_of_scienceInternational conference proceedings

Resistance of carbon nanotubes connected to reservoirs

A phase Hamiltonian of conducting carbon nanotubes with an arbitrary chirality is given which takes account of the long range Coulomb interaction and the microscopic lattice structure. By using this Hamiltonian, the transport properties at half-filling are investigated for the case that the system is adiabatically connected to reservoirs., ELSEVIER SCIENCE SA, Jun. 1999, SYNTHETIC METALS, 103 (1-3), 2527 - 2528, doi;web_of_scienceScientific journal

Persistent current and correlation effects in carbon nanotubes

The persistent current of interacting electrons in toroidal single-wall carbon nano-tubes is evaluated within Haldane's concept: of topological excitations. The overall pattern of the persistent current corresponds to the constant interaction model, whereas the fine structure stems from the electronic exchange correlations., E D P SCIENCES, Mar. 1999, EUROPHYSICS LETTERS, 45 (5), 598 - 604, doi;web_of_scienceScientific journal

Theoretical study on the charge gap of organic conductor - Bechgaard salts

The charge gap in a quarter-filled organic conductor, which is induced hy dimerization and/or alternating potential is studied by applying the renormalization group method to the bosonized one-dimensional Kamiltonian. The interplay of dimerization and alternating potential gives rise to the unconventional enhancement of the charge gap in addition to the on-site repulsive interaction. The experimental results of resistivity and optical conductivity in Bechgaard salts are examined based on the present calculation., PHYSICAL SOC JAPAN, Jun. 1999, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 68 (6), 1809 - 1812, doi;web_of_scienceUniversality of electron correlations in conducting carbon nanotubes

An effective low-energy Hamiltonian of interacting electrons in conducting single-wall carbon nanotubes with arbitrary chirality is derived from the microscopic lattice model. The parameters of the Hamiltonian show very weak dependence on the chiral angle, which makes the low-energy properties of conducting chiral nanotubes universal. The strongest Mott-Like electron instability at half filling is investigated within the self-consistent harmonic approximation. The energy gaps occur in all modes of elementary excitations and estimate at 0.01-0.1 eV. [S0163-1829(99)50616-4]., AMER PHYSICAL SOC, Apr. 1999, PHYSICAL REVIEW B, 59 (16), 10457 - 10460, doi;web_of_scienceScientific journal

Electronic properties of armchair carbon nanotubes: Bosonization approach

The phase Hamiltonian of armchair carbon nanotubes at half filling and away from it is derived from the microscopic lattice model by taking the long-range Coulomb interaction into account. We investigate the low-energy properties of the system using the renormalization group method. At half filling, the ground state is a Mott insulator with a spin gap, in which bound states of electrons are formed at different atomic sublattices., AMERICAN PHYSICAL SOC, Jan. 1999, PHYSICAL REVIEW LETTERS, 82 (2), 374 - 377, doi;web_of_scienceScientific journal

Charge density wave in a transverse electric field

A transverse electric field (a field perpendicular to the quasi-one-dimensional conducting chains) applied to a charge density wave (CDW) has similarities with a magnetic field applied to a superconductor: both cause frustration in the ordered state and, thus, can induce various intriguing states. We study the equilibrium states of CDW in a transverse electric field employing Ginzburg-Landau type effective free energy of the ordered state. We found that there are two types of CDW, corresponding to type-I and type-II superconductivity: in type-I CDW, the order is completely destroyed in the surface region as we increase the transverse field, whereas in type-II CDW the dislocations (topological defects) are created, thus avoiding the complete destruction of the order. We discuss the condition for type-I and type-II CDW., E D P SCIENCES, Dec. 1999, JOURNAL DE PHYSIQUE IV, 9 (P10), 145 - 147, web_of_scienceScientific journal

Response functions of two-coupled chains of Tomonaga-Luttinger liquids

Properties of fluctuations in two chains of Tomonaga-Luttinger liquids coupled by the interchain hopping have been studied by calculating retarded response functions chi(rho)(R)(q(x), q(y); omega) for charge and chi(sigma)(R)(q(x), q(y); omega) for spin where q(x) and q(y)(= 0 or pi) denote the longitudinal and transverse wave vector, respectively, and omega is the frequency. We have found the notable fact that the repulsive intrachain interaction results in the clear enhancement of Im chi(sigma)(R)(q(x), pi; omega) and the suppression of Im chi(rho)(R)(q(x), pi; omega) at low energies. This result indicates the importance of the dynamical effect by the spin fluctuation with q(y) = pi and small omega, which has a possibility to give rise to the attractive interaction for the electron pairing. (C) 1998 Published by Elsevier Science B.V. All rights reserved., ELSEVIER SCIENCE BV, Dec. 1998, PHYSICA C, 309 (1-2), 151 - 160, doi;web_of_scienceScientific journal

Effects of Spin Defects on Spin-Peierls Systems

We study the spin-Peierls states in the presence of spin defects for CuGeO3 where magnetic ions Cu2+ are replaced by non-magnetic ones Zn2+. Based on the action for the bosonized Hamiltonian, we investigate the spatial dependence of the phase which expresses the spin fluctuation. Further, we calculate temperature dependence of the magnetic susceptibility by taking account of the spatial variation of the phase. [spin-Peierls state, impurity effect, magnetic susceptibility, phase Hamiltonian, CuGeO3]. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved., 1998, Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu, 7, 656 - 658, doiScientific journal

Crossover between high and low energy-states in two-coupled chains of Tomonaga model

By applying the renormalization group method to two-coupled chains in the Tomonaga model, the role of interchain hopping has been studied in the entire energy region. The energy for a crossover from the perturbational regime to the relevant regime becomes smaller than that of the interchain hopping due to one-dimensional fluctuations of the mutual interaction. From the calculation of response functions for charge density waves and superconducting states, the phase diagram of dominant and subdominant states has been obtained in the plane of mutual interactions with fixed energy., KYOTO UNIV, Nov. 1997, PROGRESS OF THEORETICAL PHYSICS, 98 (5), 1045 - 1062, doi;web_of_scienceScientific journal

A study of quasi-one-dimensional conductors based on two coupled chains

Based on the bosonization method, we show that the phase transition between SDW and superconductivity of the quasi-one-dimensional organic conductors can be understood by the crossover in the two coupled chains. Further, remarkable behaviors of the charge and spin susceptibilities with the transverse wavenumber pi are calculated as a function of the longitudinal wavenumber and the frequency., ELSEVIER SCIENCE SA LAUSANNE, Feb. 1997, SYNTHETIC METALS, 85 (1-3), 1613 - 1614, doi;web_of_scienceScientific journal

Spin defects in spin-Peierls systems

We examine spin-Peierls states in the presence of spin defects for CuGeO3 where magnetic ions Cu2+ replaced by non-magnetic ones Zn2+. Based on the action for the bosonized Hamiltonian, the state is investigated by using path integral method. The temperature of spin-Peierls transition T-SP and, the spin gap and the magnitude of the averaged lattice dimerization in the ground state have been calculated as a function of doping. From comparison of the present TSP with the experimental result, a good agreement is obtained for the transition temperature of Cu-1-deltaZndeltaGeO3 in the region of the doping rate, delta < 0.02., PHYSICAL SOC JAPAN, Dec. 1997, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 66 (12), 3962 - 3969, doi;web_of_scienceScientific journal

Properties of fluctuations in two coupled chains of Luttinger liquids

Two chains of Luttinger liquids coupled by both interchain hopping and interchain interaction are investigated A degeneracy of two kinds of dominant states with in phase and out of phase ordering in the absence of the hopping is removed since the transverse fluctuation of charge density is completely gapful and that of spin density has two kinds of excitation with and without gap. The crucial effect of the interchain hopping on the electronic properties is studied by calculating susceptibilities., PLENUM PUBL CORP, Jan. 1997, JOURNAL OF LOW TEMPERATURE PHYSICS, 106 (1-2), 49 - 72, web_of_scienceScientific journal

Topological dislocations and mixed state of charge density waves

We discuss the possibility of the ''mixed state'' in incommensurate charge density waves with three-dimensional order. The mixed state is created by applying an electric field perpendicular to the chains. This state consists of topological dislocations induced by the external field and is therefore similar to the mixed states of superfluids (type-II superconductors or liquid helium II). However, the peculiar coupling of charge density waves with the electric field strongly modifies the mixed state compared to conventional superfluids. The field and temperature dependence of the properties of the mixed state are studied, and some experimental aspects are discussed., AMERICAN PHYSICAL SOC, Oct. 1996, PHYSICAL REVIEW LETTERS, 77 (16), 3403 - 3406, doi;web_of_scienceScientific journal

Spin-density wave versus superconducting fluctuations for quasi-one-dimensional electrons in two chains of Tomonaga-Luttinger liquids

We study possible states at low temperatures by applying the renormalization group method to two chains of Tomonaga-Luttinger liquids with both repulsive intrachain interactions and interchain hopping. As the energy decreases below the hopping energy, three distinct regions I, III, and II appear successively depending on properties of fluctuations. The crossover from the spin-density wave (SDW) state to superconducting (SC) state takes place in region UI where there are the excitation gaps of transverse charge and spin fluctuations. The competition between SDW and SC states in region III is crucial to understanding the phase diagram in the quasi-one-dimensional organic conductors., AMERICAN PHYSICAL SOC, Oct. 1996, PHYSICAL REVIEW B, 54 (13), 9328 - 9331, doi;web_of_scienceScientific journal

Spin-density wave versus superconducting fluctuations for quasi-one-dimensional electrons in two chains of Tomonaga-Luttinger liquids

We study possible states at low temperatures by applying the renormalization group method to two chains of Tomonaga-Luttinger liquids with both repulsive intrachain interactions and interchain hopping. As the energy decreases below the hopping energy, three distinct regions I, III, and II appear successively depending on properties of fluctuations. The crossover from the spin-density wave (SDW) state to superconducting (SC) state takes place in region III where there are the excitation gaps of transverse charge and spin fluctuations. The competition between SDW and SC states in region III is crucial to understanding the phase diagram in the quasi-one-dimensional organic conductors. © 1996 The American Physical Society., 1996, Physical Review B - Condensed Matter and Materials Physics, 54 (13), 9328 - 9331, doiScientific journal

Dielectric properties of the mixed states of charge density waves

The dielectric properties of the mixed states of charge density waves are investigated. The electric screening due to the charge density waves and the non-linear dielectric constant are studied based on the free energy of the topological dislocations, and the observation of the mixed state in condenser geometry is discussed., CZECHOSLOVAK JNL OF PHYSICS, 1996, CZECHOSLOVAK JOURNAL OF PHYSICS, 46 (Suppl. S5), 2607 - 2608, doi;web_of_scienceScientific journal

From two coupled chains to quasi-one-dimensional organic conductors

Electronic states of two coupled chains of interacting electron systems are investigated by means of phase Hamiltonian, and phase transition of quasi-one-dimensional organic conductors are discussed from the point of view of the two chains., GORDON BREACH SCI PUBL LTD, 1996, MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 285, 229 - 234, web_of_scienceScientific journal

ROLES OF INTERCHAIN HOPPING IN 2 COUPLED CHAINS OF TOMONAGA MODEL

Two chains of interacting spinless fermions in the presence of interchain hopping are investigated by use of phase Hamiltonian based on bosonization method. Excitation spectrum and phase diagram at absolute zero temperature are obtained by means of renormalization group method. Momentum distribution functions are also calculated. It is shown that the interchain hopping gives rise to drastic effects on properties of ground state compared to interchain interaction and is crucial to appearance of ordered states in higher dimensions., PHYSICAL SOC JAPAN, Oct. 1995, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 64 (10), 3811 - 3825, doi;web_of_scienceScientific journal

BOSONIZATION APPROACH TO 2 CHAINS COUPLED BY THE ELECTRON HOPPING

Based on bosonization method, the system where two chains of spinless Tomonaga model are coupled by a transverse hopping is investigated. Due to the appearance of the gap in one of the two excitations, the powers of correlation functions of charge density wave and superconductivity become just the half of those in the absence of the hopping., ELSEVIER SCIENCE SA, Apr. 1995, SYNTHETIC METALS, 71 (1-3), 1967 - 1968, doi;web_of_scienceScientific journal

SPIN MAGNETISM IN MESOSCOPIC METALS

Fluctuation of spin magnetic susceptibility square-root [deltachi(s)2] in mesoscopic metals is discussed in comparison with that of orbital magnetic susceptibility square-root [deltachi(L)2]. It is found that a ratio square-root [deltachi(s)2]/ square-root [deltachi(L)2] is independent of temperature and the boundary condition and has a magnitude of the order of (1/epsilon(F)tau)2 which is much smaller than unity, epsilon(F) and tau being Fermi energy and the relaxation time of the elastic scattering, respectively. Scattering dependent on electron spin (e.g., spin-orbit interaction or scattering by impurity spin in the glass state) are shown to suppress square-root [deltachi(s)2] far more strongly than square-root [deltachi(L)2]. The results indicate that the anomalously large fluctuation of the magnetic susceptibility compared to the average, which is expected to be observed experimentally, results from the orbital motion., PHYSICAL SOC JAPAN, Feb. 1994, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 63 (2), 405 - 408, doi;web_of_science2 COUPLED CHAINS OF TOMONAGA MODEL

Two chains of spinless Tomonaga model coupled by a transverse hopping are investigated in terms of phase Hamiltonian where separation of Fermi momentum in the presence of the hopping is taken into account explicitly. It is shown that there appears a gap in one of the two excitations by using a renormalization group method. As a result, correlation of charge density wave with interchain ordering and out of phase between the chains (superconductivity with intrachain ordering and in phase between the chains) becomes the most dominant one in the case of the repulsive (attractive) intrachain interaction., PHYSICAL SOC JAPAN, Dec. 1994, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 63 (12), 4298 - 4301, doi;web_of_scienceFLUCTUATIONS OF JOSEPHSON CURRENTS AND PERSISTENT CURRENTS IN MESOSCOPIC SPIN-GLASS SYSTEMS

Effects of correlation of the spin scattering between different measurements in the presence of the spin glass ordering have been investigated for mesoscopic fluctuations of Josephson currents in SNS junctions and those of persistent currents in isolated Aharonov-Bohm (AB) rings. It is found that, because of the absence of the time reversal symmetry, fluctuations of Josephson currents do not vanish even if the phase difference of two superconductors is zero and those of persistent currents in the absence of AB flux is also not zero. Moreover the characteristic length of exponential decay of the fluctuation of Josephson currents can be much longer than that of the average., PHYSICAL SOC JAPAN, Feb. 1993, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 62 (2), 612 - 623, doi;web_of_scienceScientific journal

PERSISTENT CURRENT OF DIRAC SEA - APPLICATION TO BISMUTH

Bismuth has been known to exhibit anomalously large diamagnetism which has been interpreted on the basis of the effective Hamiltonian of the Dirac type including spin-orbit coupling. Here the persistent current in a mesoscopic ring of bismuth is calculated. It is found that the magnetic flux induces persistent currents which have a spatial spread of the order of xi = 2hupsilon/E(g) (upsilon: velocity of the 'Dirac' electron; E(G): energy gap), just as in the atomic diamagnetism whose "atomic" size is gigantic and of mesoscopic scale., PHYSICAL SOCIETY JAPAN, Oct. 1992, JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN, 61 (10), 3462 - 3465, doi;web_of_scienceFluctuations of Josephson Currents in Mesoscopic Systems

1992, Transport Phenomena in Mesoscopic Systems, 263 - 271MESOSCOPICS AND SUPERCONDUCTIVITY

1992, New Horizons in Low-Dimensional Electron Systems, 369 - 375THE HC/E VS HC/2E OSCILLATIONS IN THE SNS JUNCTION

The Josephson current induced by the proximity effect is studied for the SNS junction with the mesoscopic Aharonov-Bohm ring in the normal region. The results shows that the critical current has a component with hc/e oscillation in addition to hc/2e oscillation, the former of which is particular to the mesoscopic system. The relative intensity of these two oscillation will be discussed for various cases., ELSEVIER SCIENCE BV, Dec. 1991, PHYSICA C, 185, 1625 - 1626, doi;web_of_scienceScientific journal

22pAC-3 Control of Strain in Shaped Graphene Nanoribbon Bridge

The Physical Society of Japan (JPS), Mar. 2015, 日本物理学会講演概要集, 70 (1), 1847Symposium

Observation of Riemannian geometrical effects on electronic states

Einstein first applied Riemannian geometry to develop the general theory of relativity almost one hundred years ago and succeeded in understanding astronomical-scale phenomena such as the straining of time-space by a gravitational field. Whether or not Riemannian space affects the electronic properties of condensed matters on a much smaller scale is of great interest. Although Riemannian geometry has been applied to quantum mechanics since the 1950s, nobody has yet answered this question, because the electronic properties of materials with Riemannian geometry have not been examined experimentally. We report here the first observation of Riemannian geometrical effects on the electronic properties of materials such as Tomononaga-Luttinger liquids, which were previously theoretically predicted by our group. We present in situ high-resolution ultraviolet photoemission spectra of a one-dimensional metallic C60 polymer with an uneven periodic peanut-shaped structure., 2012, Europhysics Letters, 98 (2), 27001, doi;urlScientific journal

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第12回物性科学領域横断研究会, 30 Nov. 2018ナノリボンの量子スピンホール状態における磁気秩序

日本物理学会2018年秋季大会, 09 Sep. 2018磁性不純物を含む二次元蜂の巣格子模型の輸送特性

日本物理学会2018年秋季大会, 09 Sep. 2018二次元蜂の巣格子単原子層物質の輸送特性

日本物理学会第73回年次大会, 2018Charge Ordering of Quarter-Filled One-Dimensional Extended Hubbard Model with π-d Coupling

ISCOM2017, 25 Sep. 2017歪み導入グラフェンの電気伝導の理論

日本物理学会第72回年次大会, 2017Haldane模型の輸送特性に対する不純物散乱の効果

日本物理学会第72回年次大会, 2017Transport properties of ribbon consisting of Haldane Model

International Conference on Topological Materials Science 2017, 2017Haldane模型の輸送特性に対する不純物散乱の効果Ⅱ

日本物理学会2017年秋季大会, 2017Transport properties of ribbon consisting of Haldane Model

International Conference on Topological Materials Science 2017, 2017局在スピンを含む一次元分子性導体における電荷秩序とそれに対する外部磁場の効果

パイ電子系物性科学の最前線, 2016Haldane模型からなる接合系の輸送特性

日本物理学会2016年秋季大会, 2016金属フラーレンポリマーにおける朝永 ラティンジャー液体理論

日本物理学会2016年秋季大会, 2016Transport properties of junctions composed of Haldane model

Yukawa Institute for Theoretical Physics (YITP) international workshop "Physics of bulk-edge correspondence and its universality: From solid state physics to cold atoms" [ BEC2016 ], 2016Transport properties of junctions composed of Haldane model

Yukawa Institute for Theoretical Physics (YITP) international workshop "Physics of bulk-edge correspondence and its universality: From solid state physics to cold atoms" [ BEC2016 ], 2016架橋構造のグラフェン・ナノリボンにおける形状による歪みのコントロール

日本物理学会 第70回年次大会, 2015局在スピンを含む一次元分子性導体における電荷秩序とそれに対する外部磁場の効果

日本物理学会 第70回年次大会, 2015BN上グラフェンへの局所1軸ひずみ導入法の開発

日本物理学会2015年秋季大会, 2015中性イオン性転移系のボゾン化による相図と低エネルギー励起の解析

日本物理学会2015年秋季大会, 2015グラフェンの電気伝導における形状効果について

日本物理学会第69回年次大会, 2014一次元分子性導体の電子状態に対する一様磁場と交替磁場の効果

日本物理学会 2014年秋季大会, 2014Theoretical Studies for effects of magnetic field on TPP[Co(Pc)(CN)2]2 and TPP[Co(Pc)(CN)2]2

大阪大学理学部花咲研究室セミナー, 2014一次元分子性導体における磁場による電荷秩序の増強Ⅱ

日本物理学会 第68回年次大会, 2013局所歪みのあるグラフェンの電気伝導測定

日本物理学会 第67回年次大会, 2012Enhancement of charge ordering by Zeeman effect in one-dimensional molecular conductors

The 19th International Conference on Magnetism with Strongly Correlated Electron Systems (SCES), 2012一次元分子性導体における磁場による電荷秩序の増強

日本物理学会 2012年秋季大会, 2012Enhancement of Charge Ordering due to External Magnetic Field in One-Dimensional Molecular Conductors

International Symposium Material Science Opened by Molecular Degree of Freedom (MDF2012), 2012Enhancement of charge ordering by Zeeman effect in one-dimensional molecular conductors

The 19th International Conference on Magnetism with Strongly Correlated Electron Systems (SCES), 2012Enhancement of Charge Ordering due to External Magnetic Field in One-Dimensional Molecular Conductors

International Symposium Material Science Opened by Molecular Degree of Freedom (MDF2012), 2012擬１次元電子系の電荷秩序状態―ボゾン化法，繰り込み群，数値的手法を組み合わせた解析―

スプリングセミナー「物性物理の現状と展望」, 2011擬一次元分子性導体の電荷秩序に対する乱れの効果

日本物理学会第66回年次大会, 2011架橋グラフェンジョセフソン接合の作製と電界効果

日本物理学会第66回年次大会, 2011Collapse of Charge Ordering Due to Disorder in Quasi One-Dimensional Electron Systems

26th International Conference on Low Temperature Physics, 2011Supercurrent through Monolayer and Multilayer Graphene

26th International Conference on Low Temperature Physics, 2011Properties of Graphene Nanoribbon with Zigzag Edges Attached to Two Normal Metals

26th International Conference on Low Temperature Physics, 2011擬一次元分子性導体の電荷秩序形成に対する乱れの効果

日本物理学会 2011年秋季大会, 2011正常金属－グラフェンナノリボン－正常金属接合系の電気伝導特性

グラフェン・ナノ構造の物理, 2011固体中のディラック電子系 －グラフェンを中心に－

2011年数学・物理学・情報科学の研究交流シンポジウム, 2011Collapse of Charge Ordering Due to Disorder in Quasi One-Dimensional Electron Systems

26th International Conference on Low Temperature Physics, 2011Supercurrent through Monolayer and Multilayer Graphene

26th International Conference on Low Temperature Physics, 2011Properties of Graphene Nanoribbon with Zigzag Edges Attached to Two Normal Metals

26th International Conference on Low Temperature Physics, 2011Effects of Disorder on Charge Ordering Transition in Quasi-One-Dimensional Molecular Conductors

International Conference on Science and Technology of Synthetic Metals 2010 (ICSM2010), 2010Superconducting proximity effect in graphene nanostructures

The International Conference on Theoretical Physics, “Dubna-Nano2010”, 2010ジグザグ型グラフェンナノリボンの磁性における異常な相互作用依存性

グラフェンと超伝導体のナノ構造に関する研究会, 2010擬一次元導体が示す朝永－Luttinger指数のバイアス電場制御

日本物理学会2010年秋季大会, 2010グラフェンにおける超伝導近接効果の理論Ⅱ

日本物理学会2010年秋季大会, 2010グラフェンにおける超伝導近接効果の理論

第18回渦糸国内会議, 2010Effects of Disorder on Charge Ordering Transition in Quasi-One-Dimensional Molecular Conductors

International Conference on Science and Technology of Synthetic Metals 2010 (ICSM2010), 2010Superconducting proximity effect in graphene nanostructures

The International Conference on Theoretical Physics, “Dubna-Nano2010”, 2010グラフェン・ナノコンストリクションの電気伝導におけるひずみ導入効果の理論

日本物理学会第76回年次大会, 15 Mar. 2021, 12 Mar. 2021, 15 Mar. 2021