  Nuclear saturation is a crucial feature in nuclear physics that plays a
fundamental role in understanding various nuclear phenomena, ranging from
properties of finite nuclei to those of neutron stars. However, a proper
description of nuclear saturation is highly nontrivial in modern
nonrelativistic~\textit{ab initio}~studies because of the elusive three-body
forces. In this letter, we calculate the equation of state for nuclear matter
in the relativistic Brueckner-Hartree-Fock (RBHF) framework with the leading
order covariant chiral nuclear force. We show that a simultaneous description
of the nucleon-nucleon scattering data and the saturation of the symmetric
nuclear matter can be achieved. In this regard, the relativistic effects nicely
explain the saturation of nuclear matter. As a result, the present study based
on the covariant chiral nuclear force shows that in the RBHF framework, one can
achieve saturation with a leading order covariant chiral nuclear force with
only two-body forces, in contrast to the vast majorities of studies in the
non-relativistic framework, where the next-to-next-to-leading order two-body
and three-body chiral forces are needed. This study sets the foundation for
studying nuclear saturation with the covariant chiral force in the RBHF
framework, which allows for a systematic understanding of one of the key
features of nuclear physics more microscopically.
