I am plotting the Riemann surface and I do expect symmetry with respect to the x and y axis, but it seems that I get only the one half of the surface
those lines give the surface
w01 = sqrt(r).*exp(1i*theta/2); % first branch
w02 = sqrt(r).*exp(1i*(theta+2*pi)/2); % second branch
(with z = re + 1j*im;
theta = angle(z); % atan2(imag(z), real(z));
r = 2*abs(z);)