  The origin of the nuclear tensor interaction in the covariant energy density
functional (EDF) is presented in this work, associated with the Fock diagrams
of Lorentz scalar and vector couplings. With this newly obtained relativistic
formalism of the nuclear tensor interaction, more distinct tensor effects are
found in the Fock diagrams of the Lorentz scalar and vector couplings, as
compared to the Lorentz pseudo-vector and tensor channels. A unified and
self-consistent treatment on both the nuclear tensor and spin-orbit
interactions, which dominate the spin-dependent features of the nuclear force,
is then achieved by the relativistic models. Moreover, careful analysis on the
tensor strengths indicates the reliability of the nuclear tensor interaction in
the covariant EDF for exploring the nuclear structure, excitation and decay
modes.
