  We theoretically investigate a non-magnetic impurity effect on the
temperature dependence of the vortex core shrinkage (Kramer-Pesch effect) in a
single-band s-wave superconductor. The Born limit and the unitary limit
scattering are compared within the framework of the quasiclassical theory of
superconductivity. We find that the impurity effect inside a vortex core in the
unitary limit is weaker than in the Born one when a system is in the moderately
clean regime, which results in a stronger core shrinkage in the unitary limit
than in the Born one.
