  We study the crossed Andreev effects in two-dimensional
conductor/superconductor hybrid systems under a perpendicular magnetic field.
Both a graphene/superconductor hybrid system and an electron gas/superconductor
one are considered. It is shown that an exclusive crossed Andreev reflection,
with other Andreev reflections being completely suppressed, is obtained in a
high magnetic field because of the chiral edge states in the quantum Hall
regime. Importantly, the exclusive crossed Andreev reflection not only holds
for a wide range of system parameters, e.g., the size of system, the width of
central superconductor, and the quality of coupling between the graphene and
the superconductor, but also is very robust against disorder. When the applied
bias is within the superconductor gap, a robust Cooper-pair splitting process
with high-efficiency can be realized in this system.
