Josephson plasma resonance in the Josephson vortex lattice in intrinsic Josephson junctions

Small phase oscillation modes of a Josephson vortex lattice in a stack of intrinsic Josephson junctions are numerically calculated. The eigenfrequency of the lowest excitation mode ω₁ is less than the zero-field plasma frequency ω_pl and is a decreasing function of the magnetic field H. The eigenfrequencies ω_n with n > ∼2 is located above ω_pl and increases with increasing H. This result is consistent with the field dependence of the Josephson plasma resonance observed in Bi-2212. We also clarify the nature of the phase oscillation modes, calculating the eigenfunctions.