Faculty Profiles - KOBAYASHI, Akito

Papers - KOBAYASHI, Akito

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Electronic Properties Close to Dirac Cone in Two-Dimensional Organic Conductor alpha-(BEDT-TTF)2I3 Reviewed

S. Katayama, A. Kobayashi, and Y. Suzumura

Eur. Phys. J. B. Vol. 67 page： 139-148 2009

Tilted-Cone-induced easy-plane pseudo-spin ferromagnet and Kosterlitz-Thouless transition in massless Dirac fermions Reviewed International coauthorship

A. Kobayashi, Y. Suzumura, H. Fukuyama, and M. O. Goerbig

J. Phys. Soc. Jpn. Vol. 78 page： 114711 2009

Theoretical study of the zero-gap organic conductor alpha-(BEDT-TTF)2I3 Reviewed

A. Kobayashi, S. Katayama, and Y. Suzumura

Sci. Technol. Adv. Mater. Vol. 10 page： 024309 2009

Hall Effect and Orbital Diamagnetism in Zerogap State of Molecular Conductor alpha-(BEDT-TTF)2I3 Reviewed

A. Kobayashi, Y. Suzumura, and H. Fukuyama

J. Phys. Soc. Jpn. 77 (2008) 064718. Vol. 77 page： 064718 2008.6

Charge ordered metal and pressure-induced superconductivity in two-dimensional organic conductor beta''-(DODHT)2PF6 Reviewed

A. Kobayashi, Y. Suzumura, M. Higa, R. Kondo, S. Kagoshima and H. Nishikawa

J. Phys.: Condens. Matter Vol. 20 page： 125205 2008.2

Role of Interlayer Electron Hopping for Spin Density Wave State in the Zero-Gap Organic Conductor Reviewed

S. Katayama, A. Kobayashi, and Y. Suzumura,

J. Phys. Soc. Jpn. Vol. 77 ( 01 ) page： 014710 2008.1

Mechanism of Superconductivity in Quasi-Two-Dimensional Organic Conductor beta-(BDA-TTP) Salts Reviewed

Y. Nonoyama, Y. Maekawa, A. Kobayashi, Y. Suzumura, and H. Ito

J. Phys. Soc. Jpn. Vol. 77 page： 094703 2008

Theory on Electronic Properties of Gapless States in Molecular Solids, α-(BEDT-TTF)2I3 Reviewed

A. Kobayashi, Y. Suzumura, and H. Fukuyama,

World Scientific Publishing Co., Pte. Ltd. Proceedings of the 9th International Symposium on Foundations of Quantum Mechanics in the Light of New Technology - ISQM-TOKYO’08 page： 168 2008

Exotic properties of zerogap state in alpha-(BEDT-TTF)2I3 Reviewed

A. Kobayashi, S. Komaba, S. Katayama, and Y. Suzumura

J. Phys.: Conf. Ser. Vol. 132 page： 012002 2008

Effect of anion potential on the zero-gap state in the two-dimensional organic conductor alpha-(BEDT-TTF)2I3 Reviewed

S. Katayama, A. Kobayashi, and Y. Suzumura,

J. Phys.: Conf. Ser. Vol. 132 page： 012003 2008

Possible mechanism to enhance spin-fluctuation-mediated superconductivity in two-dimensional organic conductor Reviewed

Y. Nonoyama, Y. Maekawa, A. Kobayashi, Y. Suzumura, and J. Yamada,

J. Phys.: Conf. Ser. Vol. 132 page： 012013 2008

Massless Fermions in Organic Conductor Reviewed

A. Kobayashi, S. Katayama, Y. Suzumura, and H. Fukuyama

J. Phys. Soc. Jpn. Vol. 76 page： 034711 2007.3

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The electronic states in two-dimensional organic conductor α-(BEDT-TTF)2I3 have been investigated to show the noticeable property of the massless fermions, i.e., the linear dispersion which exists on the contact point between the conduction band and the valence band. In the present study, we show that the effective Hamiltonian describing the massless fermions in α-(BEDT-TTF)2I3 contains intrinsically new terms of Pauli matrices σz and σ0 in addition to the Weyl equation which consists of σx and σy. The new massless fermions are robust against the charge disproportionation, and induce the anomalous momentum-dependence in the charge density.

DOI： 10.1143/JPSJ.76.034711

Role of Charge Density Wave in Superconductivity of Organic Conductor alpha-(BEDT-TTF)2NH4Hg(SCN)4 Salt Reviewed

Y. Nonoyama, A. Kobayashi, and Y. Suzumura

J. Phys. Soc. Jpn. Vol. 76 page： 014703 2007.1

Pairing mechanisms in quasi-two-dimensional organic superconductor Reviewed

A. Kobayashi, Y. Nonoyama, and Y. Suzumura,

J. Magn. Mag. Mat. 310 (2007) 1090-1092. Vol. 310 page： 1090-1092. 2007

Electric Conductivity of the Zero-Gap Semiconducting State in alpha-(BEDT-TTF)2I3 Salt Reviewed

S. Katayama, A. Kobayashi and Y. Suzumura,

J. Phys. Soc. Jpn. 75 (2006) 023708. Vol. 75 page： 023708 2006.10

Pressure-Induced Zero-Gap Semiconducting State in Organic Conductor alpha-(BEDT-TTF)2I3 Salt Reviewed

S. Katayama, A. Kobayashi and Y. Suzumura

J. Phys. Soc. Jpn. Vol. 75 page： 054705 2006.5

Language：English Publishing type：Research paper (scientific journal)

We show a zero-gap semiconducting (ZGS) state in the quasi-two-dimensional organic conductor α-(BEDT-TTF)2I3 salt, which emerges under uniaxial pressure along the a-axis (the stacking axis of the BEDT-TTF molecule). The ZGS state is the state in which a Dirac cone with the band spectrum of a linear dispersion exists around the Fermi point connecting an unoccupied (electron) band with an occupied (hole) band. The spectrum exhibits a large anisotropy in velocity, which depends on the direction from the Fermi point. By varying the magnitude of several transfer energies of a tight-binding model with four sites per unit cell, it is shown that the ZGS state exists in a wide pressure range, and is attributable to the large anisotropy of the transfer energies along the stacking axis.

DOI： 10.1143/JPSJ.75.054705

Superconductivity in Charge Ordered Metal for Quasi-2D Organic Conductor Reviewed

A. Kobayashi, S. Katayama and Y. Suzumura

J. Phys. Soc. Jpn. 74 (2005) 2897-2900. Vol. 74 page： 2897-2900 2005

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The superconductivity that occurs below the charge ordering temperature in a quasi-two-dimensional (quasi-2D) organic conductor, the α-(ET)2I3 salt, has been examined by applying the mean field theory and the random phase approximation to the extended Hubbard model with four sites in the unit cell and anisotropic nearest-neighbor interactions. It is shown that, under uniaxial pressure, the insulating phase moves to the metal phase with small pockets of electrons and holes, while the charge ordering state with the horizontal stripe pattern is retained. The novel property of the metal phase gives rise to the superconducting (SC) state with the full gap. It is found that the pairing interaction for the superconductivity is given mainly by the spin fluctuation existing between hole-rich sites in the unit cell. The role of the anisotropic repulsive interaction is discussed for the mechanism of the present SC state.

DOI： 10.1143/JPSJ.74.2897

On the Magnetic Excitation Spectra of High Tc Cu Oxides at Energies Up to the Region Far above the Resonance Energy Reviewed

S. Iikubo, M. Ito, A. Kobayashi, M. Sato and K. Kakurai,

J. Phys. Soc. Jpn. 74 (2005) 275-278 Vol. 74 page： 275-278 2005

Charge fluctuation induced superconductivity in alpha-(ET)_2I_3 salt Reviewed

A. Kobayashi, S. Katayama, K. Noguchi, and Y. Suzumura,

Physica B 359-361 (2005) 451. Vol. 359-361 page： 451. 2005

Coherent and incoherent states in the d-p model Reviewed

A. Tsuruta, A. Kobayashi, T. Matsuura, Y. Kuroda,

Physica B Vol. 359-361 page： 774 - 776 2005

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Papers - KOBAYASHI, Akito