Improve quality in 3d plots with pgfplots package

Question

I tried the following code

\begin{axis}[
    hide axis,
    colormap/cool,
]
\addplot3[
    surf,
    samples=101,
    domain=-1.1:0.5,
]
{sqrt(x^2+x^3-y^2)};
\end{axis}
\end{tikzpicture}

But the quality I get is terrible:.

It should look more like the following image divided by half: .

I also tried using mesh instead of surf but it didn't work either.