  Transition metal dichalcogenides (TMDCs) heterostructure with a type II
alignment hosts unique interlayer excitons with the possibility of spin-triplet
and spin-singlet states. However, the associated spectroscopy signatures remain
elusive, strongly hindering the understanding of the Moire potential modulation
of the interlayer exciton. In this work, we unambiguously identify the
spin-singlet and spin-triplet interlayer excitons in the WSe2/MoSe2
hetero-bilayer with a 60-degree twist angle through the gate- and magnetic
field-dependent photoluminescence spectroscopy. Both the singlet and triplet
interlayer excitons show giant valley-Zeeman splitting between the K and K'
valleys, a result of the large Lande g-factor of the singlet interlayer exciton
and triplet interlayer exciton, which are experimentally determined to be ~
10.7 and ~ 15.2, respectively, in good agreement with theoretical expectation.
The PL from the singlet and triplet interlayer excitons show opposite
helicities, determined by the atomic registry. Helicity-resolved
photoluminescence excitation (PLE) spectroscopy study shows that both singlet
and triplet interlayer excitons are highly valley-polarized at the resonant
excitation, with the valley polarization of the singlet interlayer exciton
approaches unity at ~ 20 K. The highly valley-polarized singlet and triplet
interlayer excitons with giant valley-Zeeman splitting inspire future
applications in spintronics and valleytronics.
