  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, $(2m_l+1)\pi$ phase kinks with integers $m_l$'s stack along the c
axis and lock neighboring junction together. Large dc power is pumped into
plasma oscillation via kinks at the cavity resonance. 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.
