  Using the C* algebraic scattering approach to study quasifree fermionic
systems out of equilibrium in quantum statistical mechanics, we construct the
nonequilibrium steady state in the isotropic XY chain whose translation
invariance has been broken by a local magnetization and analyze the asymptotic
behavior of the expectation value for a class of spatial correlation
observables in this state. The effect of the breaking of translation invariance
is twofold. Mathematically, the finite rank perturbation not only regularizes
the scalar symbol of the invertible Toeplitz operator generating the leading
order exponential decay but also gives rise to an additional trace class Hankel
operator in the correlation determinant. Physically, in its decay rate, the
nonequilibrium steady state exhibits a left mover--right mover structure
affected by the scattering at the impurity.
