  We construct a hadron-quark two-phase model based on the Walecka-quantum
hadrodynamics and the improved Polyakov-Nambu--Jona-Lasinio model with an
explicit chemical potential dependence of Polyakov-loop potential ($\mu$PNJL
model). With respect to the original PNJL model, the confined-deconfined phase
transition is largely affected at low temperature and large chemical potential.
Using the two-phase model, we investigate the equilibrium transition between
hadronic and quark matter at finite chemical potentials and temperatures. The
numerical results show that the transition boundaries from nuclear to quark
matter move towards smaller chemical potential (lower density) when the
$\mu$-dependent Polyakov loop potential is taken. In particular, for charge
asymmetric matter, we compute the local asymmetry of $u, d$ quarks in the
hadron-quark coexisting phase, and analyse the isospin-relevant observables
possibly measurable in heavy-ion collision (HIC) experiments. In general new
HIC data on the location and properties of the mixed phase would bring relevant
information on the expected chemical potential dependence of the Polyakov Loop
contribution.
