  The interplay between electronic orders and superconductivity is central to
the physics of unconventional superconductors, and is particularly pronounced
in the iron-based superconductors. Motivated by recent experiments on FeSe, we
study the superconducting pairing in its nematic phase in a multiorbital model
with frustrated spin-exchange interactions. The electron correlations in the
presence of the nematic order give rise to an enhanced orbital selectivity in
the superconducting pairing amplitudes. This orbital-selective pairing produces
a large gap anisotropy on the Fermi surface. Our results naturally explain the
striking experimental observations, and shed new light on the unconventional
superconductivity of correlated electron systems in general.
