研究等業績 - 原著論文 - 林　正彦

Theory of the Strain Engineering of Graphene Nanoconstrictions

Masahiko Hayashi, Hideo Yoshioka, Hikari Tomori, Akinobu Kanda

Journal of the Physical Society of Japan ( Physical Society of Japan )  90 ( 2 ) 23701 - 23701   2021年02月  [査読有り]

研究論文（学術雑誌）   国内共著

Magnetic Phase Diagram of a Superconducting Bilayer Disk: Effects of Geometrical Modification

Masahiko Hayashi

Journal of the Physical Society of Japan ( Journal of the Physical Society of Japan )  89 ( 10 )   2020年10月  [査読有り]

研究論文（学術雑誌）   単著

DOI

SQUID microscopy for mapping vector magnetic fields

Vu T.D.

Superconductor Science and Technology ( Superconductor Science and Technology )  32 ( 11 )   2019年09月  [査読有り]

研究論文（学術雑誌）   国内共著

DOI

Effects of Fluctuations on the Phase Diagram of the t–J Model

Masahiko Hayashi

Journal of the Physical Society of Japan ( Japan Society of Applied Physics )  88 ( 9 ) 094703   2019年09月  [査読有り]

研究論文（学術雑誌）   単著

DOI CiNii Research

A Model of Competing Orders and Its Application to a Novel Jucntion

Masahiko Hayashi

Journal of Superconductivity and Novel Magnetism   32   3407 - 3413   2019年05月  [査読有り]

研究論文（学術雑誌）   単著

DOI

Effects of Interlayer Coupling on the Magnetic Flux of Vortices in Bi-layer Superconductors

Masahiko Hayashi

Journal of the Physical Society of Japan ( Japan Society of Applied Physics )  88 ( 3 ) 035002   2019年03月  [査読有り]

研究論文（学術雑誌）   単著

DOI CiNii Research

Confined vortices in de facto mesoscopic Mo80Ge20 disks with sector defects

The Dang Vu, Ho Thanh Huy, Atsuki Ito, Masaki Toji, Hiroaki Shishido, Masaru Kato, Masahiko Hayashi, Takekazu Ishida

Superconductor Science and Technology   31   125009   2018年11月  [査読有り]

研究論文（学術雑誌）   国内共著

We introduce a sectoral defect into a disk (creating a Pac-Man™-shaped plate) to investigate effect of the symmetry breaking of a perfect disk on vortex dynamics. The sectoral defect acts as a preferential gateway for vortices to enter the disk. Vortices tend to form a symmetric configuration with respect to the mirror-symmetry line under various different applied magnetic fields. We found that the vortex configuration of the Pac-Man™-shaped disk exhibits an exotic arc structure, in contrast to the well-known shell structure of a disk. A characteristic of the vortex configuration is the critical number of vortices (or 'magic number') at which the single-arc structure becomes a multiple-arc structure, which can be tuned by changing the opening angle of the sectoral defect. We also noticed by comparing the free energies of the vortex distributions, that there are several competing metastable states with the same number of vortices when the ratio of the number of vortices in the outer arc to the number in the inner arc approaches two, for which stable triangular clusters might form part of the configurations. We conclude that there are reasonable agreements between the Ginzburg–Landau calculations and experimental scanning SQUID microscope images of vortices in de facto mesoscopic Pac-Man™-shaped Mo80Ge20 thin disks.

DOI

Vector sensor for scanning SQUID microscopy

Vu The Dang, Masaki Toji, Ho Thanh Huy, Shigeyuki Miyajima, Hiroaki Shishido, Mutsuo Hidaka, Masahiko Hayashi, Takekazu Ishida

Journal of Physics: Conf. Series   871   012075   2017年07月  [査読有り]

研究論文（学術雑誌）   国内共著

DOI

Time-Dependent Ginzburg–Landau Equation and Boltzmann Transport Equation for Charge-Density-Wave Conductors

Yoshitake Takane, Masahiko Hayashi, Hiromichi Ebisawa

Journal of the Physical Society of Japan   85   084709   2016年07月  [査読有り]

研究論文（学術雑誌）   国内共著

The time-dependent Ginzburg–Landau equation and the Boltzmann transport equation for charge-density-wave (CDW) conductors are derived from a microscopic one-dimensional model by applying the Keldysh Green’s function approach under a quasiclassical approximation. The effects of an external electric field and impurity pinning of the CDW are fully taken into account without relying on a phenomenological argument. These equations simultaneously describe the spatiotemporal dynamics of both the CDW and quasiparticles; thus, they serve as a starting point to develop a general framework to analyze various nonequilibrium phenomena, such as current conversion between the CDW condensate and quasiparticles, in realistic CDW conductors. It is shown that, in typical situations, the equations correctly describe the nonlinear behavior of electric conductivity in a simpler manner.

DOI

Time-dependent Ginzburg–Landau equation of charge-density-waves and numerical simulation of the slidingOriginal Research Article

Masahiko Hayashi, Yositake Takane, Hiromichi Ebisawa

Physica B   460   6 - 10   2015年03月

研究論文（学術雑誌）   国内共著

Time-dependent Ginzburg-Landau equation (TDGL) for charge-density-wave (CDW) conductors is discussed. At first, we study a purely one-dimensional case, where the current electrodes are attached from the sides. One of the characteristics of our TDGL is that the non-equilibrium chemical potential for right-moving and left-moving electrons are taken into account as dynamical variables. Then the dynamical interaction between the condensate and the quasiparticles is demonstrated in an apparent form. We present some results of the numerical simulation of the sliding of CDW based on our TDGL. Possible extension to quasi-one dimensional (three-dimensional) systems is also discussed.

Supercurrent through Graphene: Effects of Vanishing Density of States

M. Hayashi, H. Yoshioka, A. Kanda

J. Phys.: Conf. Ser.   400   022024   2012年12月  [査読有り]

研究論文（学術雑誌）   国内共著

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.

Numerical Study of Collective Transport in Charge Density Wave Conductors

M. Hayashi, Y. Takane, H. Ebisawa

J. Phys.: Conf. Ser.   400   012015   2012年12月  [査読有り]

研究論文（学術雑誌）   単著

We present the results of numerical simulation of the sliding conduction of charge density wave using newly derived time-dependent equations of motion of the Ginzburg-Landau type. In this analysis, the quasi-particle fluctuation modes are treated as independent variables and electron injection to and extraction from the charge density wave conductor are directly simulated.

Superconducting proximity effect in graphene nanostructures

M. Hayashi, Y. Takane, H. Ebisawa

J. Phys.: Conf. Ser.   248   012002   2010年07月  [査読有り]

研究論文（学術雑誌）   国内共著

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 junction is also given and both monolayer and bilayer junctions show some characteristic deviations.

Topological Defect and Quasi-particle Dynamics in Charge Density Waves

M. Hayashi, H. Ebisawa

Physica C   470   S962 - S963   2010年01月  [査読有り]

研究論文（学術雑誌）   国内共著

The dynamics of topological defects (dislocations) in charge density waves (CDW’s) is largely affected by the quasi-particle dynamics in the cores of the dislocations. The dislocations mediate the conversion of the electron number between condensate and quasi-particle sub-systems. This is especially important in the sliding conduction of CDW. In this work we propose a simple model, which is obtained by extending the Ginzburg–Landau theory partially taking into account the quasi-particle dynamics in the sense of two-fluid model. We perform the numerical simulation of sliding conduction of CDW based on our model. Using this model we may clarify the detailed process of dislocation nucleation and annihilation near the contacts.

Theoretical Study of Superconducting Proximity Effect in Single and Multi-layered Graphene

M. Hayashi, H. Yoshioka, A. Kanda

Physica C   470   S846 - S847   2010年01月  [査読有り]

研究論文（学術雑誌）   国内共著

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.