研究者詳細 - 小林　晃人

論文 - 小林　晃人

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

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

Eur. Phys. J. B. 67 巻頁： 139-148 2009年

Tilted-Cone-induced easy-plane pseudo-spin ferromagnet and Kosterlitz-Thouless transition in massless Dirac fermions 査読有り国際共著

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

J. Phys. Soc. Jpn. 78 巻頁： 114711 2009年

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

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

Sci. Technol. Adv. Mater. 10 巻頁： 024309 2009年

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

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

J. Phys. Soc. Jpn. 77 (2008) 064718. 77 巻頁： 064718 2008年6月

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

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

J. Phys.: Condens. Matter 20 巻頁： 125205 2008年2月

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

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

J. Phys. Soc. Jpn. 77 巻 ( 01 ) 頁： 014710 2008年1月

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

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

J. Phys. Soc. Jpn. 77 巻頁： 094703 2008年

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

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 頁： 168 2008年

Exotic properties of zerogap state in alpha-(BEDT-TTF)2I3 査読有り

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

J. Phys.: Conf. Ser. 132 巻頁： 012002 2008年

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

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

J. Phys.: Conf. Ser. 132 巻頁： 012003 2008年

Possible mechanism to enhance spin-fluctuation-mediated superconductivity in two-dimensional organic conductor 査読有り

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

J. Phys.: Conf. Ser. 132 巻頁： 012013 2008年

Massless Fermions in Organic Conductor 査読有り

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

J. Phys. Soc. Jpn. 76 巻頁： 034711 2007年3月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

J. Phys. Soc. Jpn. 76 巻頁： 014703 2007年1月

Pairing mechanisms in quasi-two-dimensional organic superconductor 査読有り

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

J. Magn. Mag. Mat. 310 (2007) 1090-1092. 310 巻頁： 1090-1092. 2007年

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

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

J. Phys. Soc. Jpn. 75 (2006) 023708. 75 巻頁： 023708 2006年10月

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

S. Katayama, A. Kobayashi and Y. Suzumura

J. Phys. Soc. Jpn. 75 巻頁： 054705 2006年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

A. Kobayashi, S. Katayama and Y. Suzumura

J. Phys. Soc. Jpn. 74 (2005) 2897-2900. 74 巻頁： 2897-2900 2005年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

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 査読有り

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

J. Phys. Soc. Jpn. 74 (2005) 275-278 74 巻頁： 275-278 2005年

Charge fluctuation induced superconductivity in alpha-(ET)_2I_3 salt 査読有り

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

Physica B 359-361 (2005) 451. 359-361 巻頁： 451. 2005年

Coherent and incoherent states in the d-p model 査読有り

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

Physica B 359-361 巻頁： 774 - 776 2005年

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