Josephson plasma and Josephson vortex lattice in high T_c superconductors with an applied magnetic field parallel to the layers

By use of the multi-Josephson junction model, we investigate Josephson plasma modes in the high T_c superconductor with an applied magnetic field parallel to the layers. The capacitive and inductive effects are considered as inter-layer couplings. By numerical simulations, we obtain stable lattice structure of Josephson vortices, and calculate the spectrum of the Josephson plasma modes. It is shown that the triangular lattice of vortices is stable at high magnetic field, but it is distorted for H≤H _cr∼Φ₀/(2πλD), where Φ₀ is the unit flux, λ the penetration depth along the ab-plane and D the depth of the insulating layer. We identify two observable Josephson plasma modes; the higher mode increases with H, while the lower mode takes the maximum at H = H_cr and decreases with increasing H.