  We have studied tunneling-mediated local density of states (LDOS) of the
surface layer of a bilayer cuprate, where a Zn impurity is located on the
second Cu-O layer. When the tunneling strength between two Cu-O layers is
larger than a critical value, the LDOS on the site just above the Zn impurity
first exhibits a resonant peak near the Fermi surface. The larger the tunneling
strength, the stronger the resonant peak. It is also shown that the height of
the resonant peak oscillates decreasingly with the distance from the site just
above the Zn impurity. The location of the resonant peak in the surface LDOS
depends on doping, energy gap, and the tunneling strength, and has an opposite
bias voltage to that on its nearest neighboring sites. The results could be
tested by the STM experiments and be used to further understand the electronic
properties of high temperature superconductors.
