Kink state in a stack of intrinsic Josephson junctions in layered high-T _c superconductors and terahertz radiation

A new family of dynamic states are found in a stack of inductively coupled intrinsic Josephson junctions in the absence of an external magnetic field. In this state, (2m _l +1)π phase kinks with integers m _l 's stack along the c axis and lock neighboring junctions together. A significant part of the dc power is pumped into plasma oscillations via kinks at the cavity resonances. The plasma oscillation is uniform along the c axis with the frequency satisfying the ac Josephson relation. Thus this state supports strong terahertz radiation and seems to be compatible with the recent experimental observations.