I-V characteristics and optical properties in high-T_c superconductors with alternating junction parameters

We investigate the longitudinal phase dynamics in an intrinsic Josephson-junction array with alternating junction parameters on the basis of the capacitive coupling model. The coupled dynamical equations for the phase differences are derived. The linear dynamics in this system yields two collective phase modes propagating along the c-direction, which are identified with the two longitudinal Josephson-plasma modes observed in the T ^*-structure high-T_c cuprates. The non-linear phase dynamics in this system shows the existence of stable localized rotating modes, which leads to the multiple branch structure in the I-V characteristics. On the basis of the numerical results we predict the I-V characteristics of the T ^*-structure high-T_c cuprates.