  Interlayer excitons in transition-metal dichalcogenide heterobilayers combine
high binding energy and valley-contrasting physics with long optical lifetime
and strong dipolar character. Their permanent electric dipole enables
electric-field control of emission energy, lifetime, and location. Device
material and geometry impacts the nature of the interlayer excitons via their
real- and momentum-space configurations. Here, we show that interlayer excitons
in MoS$_{2}$/MoSe$_{2}$ heterobilayers are formed by charge carriers residing
at the Brillouin zone edges, with negligible interlayer hybridization. We find
that the moir\'e superlattice leads to the reversal of the valley-dependent
optical selection rules, yielding a positively valued g-factor and
cross-polarized photoluminescence. Time-resolved photoluminescence measurements
reveal that the interlayer exciton population retains the optically induced
valley polarization throughout its microsecond-long lifetime. The combination
of long optical lifetime and valley polarization retention makes
MoS$_{2}$/MoSe$_{2}$ heterobilayers a promising platform for studying
fundamental bosonic interactions and developing excitonic circuits for optical
information processing.
