  We report on the existence of nonlinear surface waves which, on the one hand,
do not require the threshold energy flow for their excitation, and, on the
other hand, extend into media at both sides of the interface at low powers,
i.e. can not be reduced to the conventional Tamm states. Such waves can be
excited if the refractive index in at least one of the materials forming the
interface is periodically modulated, with properly selected modulation depth
and frequency. Thresholdless surface solitons can be stable in the entire
existence domain.
