  While the Polyakov loop is an order parameter of the deconfinement transition
in the heavy quark mass regime of QCD, its sensitivity to the deconfinement of
light, dynamical quarks in QCD is not apparent. On the other hand, the quark
mass dependence of the Polyakov loop is sensitive to the appearance of a chiral
phase transition. Using lattice QCD calculations in the staggered fermion
discretization scheme at finite values of the lattice spacing, $aT = 1/8$, we
show here, for the first time, that the Polyakov loop expectation value, and
the heavy quark free energy extracted from it, behave like energy-like
observables in the vicinity of the chiral phase transition temperature $T_c$.
Consistent with scaling behavior of energy-like observables in the 3-$d$, O(2)
universality class, the quark mass derivatives diverge in the chiral limit at
$T_c$ while the temperature derivatives stay finite. The latter will develop a
characteristic spike at $T_c$. This, however, may be resolved only in
calculations with quark masses being two orders of magnitude smaller than those
currently accessible in lattice QCD calculations.
