  Recently novel current-driven resonant states characterized by the
$\pi$-phase kinks were proposed in the coupled sine-Gordon equation. In these
states hysteresis behavior is observed with respect to the application process
of current, and such behavior is due to nonlinearity in the sine term. Varying
strength of the sine term, there exists a critical strength for the hysteresis
behavior and the amplitude of the sine term coincides with the applied current
at the critical strength.
