  We present here a novel and testable mechanism for leptogenesis, which is
characterized by a purely thermal generation of lepton asymmetry via scalar
decay. Guided by the thermal mass matrix diagonalization in the
finite-temperature regime, we propose a scenario in which the baryon asymmetry
is formulated in terms of the masses and mixing from hierarchical Dirac
neutrinos, as well as a vacuum scale accountable for the sub-eV neutrino
masses. This allows a natural and direct link between the high-scale
\textit{CP} asymmetry and the low-energy Dirac \textit{CP}-violating phase
without involved model structures, and thus circumvents the haunting problem
encountered in general leptogenesis scenarios. The mechanism can also be
applied as a prototype for solving the baryon asymmetry problem to a broad
class of well-motivated model buildings.
