  The superconductivity of high transition temperature (Tc) occurs in copper
oxides with carrier-doping to an antiferromagnetic (AF) Mott insulator. This
discovery more than thirty years ago immediately led to a prediction about the
formation of a small Fermi pocket. This structure, however, has not yet been
detected, while it could be a key element in relating high-Tc superconductivity
to Mott physics. To address this long-standing issue, we investigate the
electronic structure of a five-layered Ba2Ca4Cu5O10(F,O)2 with inner CuO2
planes demonstrated to be cleanest ever in cuprates. Most surprisingly, we find
small Fermi surface (FS) pockets closed around (pi/2,pi/2) consistently by
angle-resolved photoemission spectroscopy (ARPES) and quantum oscillation
measurements. The d-wave superconducting gap opens along the pocket, revealing
the coexistence between the superconductivity and AF order in the same CuO2
sheet. Our data further indicate that the superconductivity can occur without
contribution from the states near the antinodal region, which are shared by
other competing excitations such as the charge density wave (CDW) and pseudogap
states. This will have significant implications for understanding the
superconductivity and puzzling Fermi arc phenomena in cuprates.
