  How does Fermi surface develop in cuprates upon doping of a parent Mott
insulator, does it consist of large barrels or small pockets, which of them is
responsible for superconductivity and what is a role of the pseudogap? Those
are actively debated questions, important for understanding of high temperature
superconductivity. Here we analyze doping dependence of interlayer tunneling in
cuprates. We observe that with decreasing doping the supercurrent is rapidly
decreasing, but the quasiparticle resistance at high bias remains almost
unchanged. This indicates that Cooper pair and quasiparticle currents originate
from different parts of Brillouin zone: Cooper pairs are residing only on small
pockets, which are progressively shrinking with decreasing doping, but the
quasiparticle current is integrated over the full length of barrels, which are
only weakly doping dependent. The expanding pseudogap areas along the barrels
do not contribute to pair current. This provides direct evidence for
nonsuperconducting origin of the pseudogap.

Superconductivity