Ayumi Fujita

Numerical study for vortex lattice transition in d-wave superconductors with extended Ginzburg–Landau model

Abstract We study the vortex lattice structure in two-dimensional d-wave superconductors in a magnetic field perpendicular to the x-, y-plane. The numerical simulation for the extended Ginzburg–Landau Hamiltonian is carried out with the Langevin equation. In the moderate low-temperature phase the vortex triangular lattice is obtained, subsequently the oblique vortex lattice becomes stable in further low-temperature phase. The Abrikosov factor shows an anomalous kink at the transition point.

Langevin simulation of the nonlocal Ginzburg–Landau model for superconductors in a magnetic field

We investigate the vortex state for the unconventional superconductors by numerical simulation of the phenomenological nonlocal Ginzburg-Landau Hamiltonian using Langevin equation. We obtain rhomboid vortex lattice structure which is very near to the square lattice in the low temperatures. We evaluate the specific heat and obtain a cusp which indicates the melting of the vortex lattice.

Numerical study for vortex lattice transition with extended Ginzburg-Landau model

Abstract We study the vortex lattice structure in two dimensional d -wave superconductors in a magnetic field which is perpendicular to the a – b plane. The numerical simulation for the extended Ginzburg–Landau Hamiltonian, which introduces the fourth order derivative terms, is carried out with the Langevin equation. As we increase the effect of these nonlocal terms, the triangular vortex lattice is distorted and vortices form isosceles triangular pattern with no long range order.

MATRIX MODEL APPROACH TO THE FLUX-LATTICE MELTING IN TWO-DIMENSIONAL SUPERCONDUCTORS

We investigate a gauged matrix model in the large-{ital N} limit that is closely related to the superconductor fluctuation and the flux-lattice melting in two dimensions. With the use of the saddle-point method, the free energy is expanded up to eighth order for the coupling constant {ital g}. In the case that the coefficient of the quadratic term of the Ginzburg-Landau matrix model is negative, a critical point {ital g}={ital g}{sub {ital c}} is obtained in the large-{ital N} limit and the relation between this phase transition and the two-dimensional flux-lattice melting transition is discussed.

Disorder effect on flux lattice melting near Hc2

Abstract The perturbation series for the three dimensional free energy of Ginzburg-Landau model in a random potential is investigated for a strong magnetic field. The shift of the melting temperature of vortex lattice caused by the white noise random potential is evaluated. The crossover between the “vortex-glass” phase and the “gauge-glass” phase is discussed for a strong disorder.

Fluctuation of the specific heat for the superconductors near HC2

The specific heat transition in a strong magnetic field for superconductor is discussed by a scaling function. The perturbation series is evaluated for this scaling function. In particular, the perturbation series up to the eleventh order is obtained for the two dimensional case. The large order behavior is derived theoretically and it is shown that this behavior is not related to the Abrikosov lattice.