arXiv subjects
Publications and source records attributed to Tomio Koyama.
We propose a generalized London theory that can correctly describe the longitudinal and transverse responses of conventional superconductors to an electromagnetic field. The continuity equation is satisfied by use of a special gauge for the scalar and vector potentials. Our phenomenological theory provides a simple example of the Anderson-Higgs mechanism.
We have developed a numerical method that calculated superconducting states and magnetic field distributions for the composite structures of the High-Tc superconductor and the conventional superconductor in arbitrary geometries. We show spontaneous magnetic flux appears at the corner of the boundary of these two superconductors. Also we propose High-Tc superconducting dot embedded in conventional superconductors, which is named as d-dot and show the spatial distribution of superconducting order parameters and the magnetic field.
We investigate the extended quasi-particle states in the mixed state of d-wave superconductors on the basis of the Bogoliubov-de Gennes equation. We prove that the quasi-particle eigen-states can be classified in terms of new topological quantum numbers which are related to the topological nature of the non-trivial phases of the quasi-particles. Numerical results for the quasi-particle eigen-states reveal the crossover behavior from gapless to gapped states as the flux density $B$ increases. In the strong field region quantum oscillations appear in the excitation energy of the quasi-particles.