  We present a corrective subcell averaging technique that improves on the
accuracy of the volume-averaged finite-difference time-domain (FDTD) method in
the presence of dispersive material interfaces. The method is based on an
alternative effective-medium formulation that captures field discontinuities at
interfaces as electric and magnetic surface currents. In calculating the
spectra of strongly dispersive Mie scatterers we demonstrate that the derived
FDTD algorithm is both highly efficient and able to approximately restore
second order accuracy.
