  We use scanning tunneling microscopy to visualize the atomic-scale electronic
states induced by a pair of hole dopants in Ca2CuO2Cl2 parent Mott insulator of
cuprates. We find that when the two dopants approach each other, the transfer
of spectral weight from high energy Hubbard band to low energy in-gap state
creates a broad peak and nearly V-shaped gap around the Fermi level. The peak
position shows a sudden drop at distance around 4 a0 and then remains almost
constant. The in-gap states exhibit peculiar spatial distributions depending on
the configuration of the two dopants relative to the underlying Cu lattice.
These results shed important new lights on the evolution of low energy
electronic states when a few holes are doped into parent cuprates.
