  Mobility edge (ME) has played an essential role in disordered models.
However, while this concept has been well established in disordered
single-particle models, its existence in disordered many-body models is still
under controversy. Here, a general approach based on coupling between extended
and localized states in their overlapped spectra for ME is presented. We show
that in the one-dimensional (1d) disordered single-particle models, all states
are localized by direct coupling between them. However, in $d \ge 2$ disordered
single-particle and 1d disordered many-body models, the resonant hybridization
between these states in their overlapped spectra makes all states be extended,
while these in the un-overlapped spectra are unchanged, leading to tunable MEs.
We propose several models, including two disordered many-body spin models, to
verify this mechanism. Our results establish a unified mechanism for MEs and
demonstrate its universality in single-particle and many-body models, which
opens an intriguing avenue for the realization and verification of MEs in
many-body localization.
