The free energy between a static quark and an antiquark is studied by using
the color-singlet Polyakov-line correlation at finite temperature. We perform
simulations on 323×12, 10, 8, 6, 4 lattices in the high temperature
phase with the RG-improved gluon action and 2+1 flavors of the clover-improved
Wilson quark action. Since the simulations are based on the fixed scale
approach that the temperature can be varied without changing the spatial volume
and renormalization factor, it is possible to investigate temperature
dependence of the heavy-quark free energy without any adjustment of the overall
constant. We find that, the heavy-quark free energies at short distance
converge to the heavy-quark potential evaluated from the Wilson-loop operator
at zero temperature, in accordance with the expected insensitivity of short
distance physics to the temperature. At long distance, the heavy-quark free
energies approach to twice the single-quark free energies, implying that the
interaction between heavy quarks is screened. The Debye screening mass obtained
from the long range behavior of the heavy-quark free energy is compared with
results of the thermal perturbation theory and those of Nf​=2 and Nf​=0
lattice simulations.Comment: To appear in the proceedigns of 27th International Symposium on
Lattice Field Theory (Lattice 2009), Beijing, China, 25-31 July 200