  We investigate the physical properties of an integrable extension of the
Hubbard model with a free parameter $\gamma$ related to the quantum deformation
of the superalgebra $sl(2|2)^{(2)}$. The Bethe ansatz solution is used to
determine the nature of the spin and charge excitations. The dispersion
relation of the charge branch is given by a peculiar product between
energy-momenta functions exhibiting massless and massive behaviors. The study
of the finite-size corrections to the spectrum reveals us that the underlying
conformal theory has central charge $c=-1$ and critical exponents depending on
the parameter $\gamma$. We note that exact results at the isotropic point
$\gamma=0$ can be established without recourse to the Bethe ansatz solution.
