  We study the main nonlinear solutions of plasmonic slot waveguides made from
an anisotropic metamaterial core with a positive Kerr-type nonlinearity
surrounded by two semi-infinite metal regions. First, we demonstrate that for a
highly anisotropic diagonal elliptical core, the bifurcation threshold of the
asymmetric mode is reduced from GW/m threshold for the isotropic case to 50
MW/m one indicating a strong enhancement of the spatial nonlinear effects, and
that the slope of the dispersion curve of the asymmetric mode stays positive,
at least near the bifurcation, suggesting a stable mode. Second, we show that
for the hyperbolic case there is no physically meaningful asymmetric mode, and
that the sign of the effective nonlinearity can become negative.
