  The atomic-level vdW heterostructures have been one of the most interesting
quantum material systems, due to their exotic physical properties. The
interlayer coupling in these systems plays a critical role to realize novel
physical observation and enrich interface functionality. However, there is
still lack of investigation on the tuning of interlayer coupling in a
quantitative way. A prospective strategy to tune the interlayer coupling is to
change the electronic structure and interlayer distance by high pressure, which
is a well-established method to tune the physical properties. Here, we
construct a high-quality WS2/MoSe2 heterostructure in a DAC and successfully
tuned the interlayer coupling through hydrostatic pressure. Typical
photoluminescence spectra of the monolayer MoSe2 (ML-MoSe2), monolayer WS2
(ML-WS2) and WS2/MoSe2 heterostructure have been observed and it's intriguing
that their photoluminescence peaks shift with respect to applied pressure in a
quite different way. The intralayer exciton of ML-MoSe2 and ML-WS2 show blue
shift under high pressure with a coefficient of 19.8 meV/GPa and 9.3 meV/GPa,
respectively, while their interlayer exciton shows relative weak pressure
dependence with a coefficient of 3.4 meV/GPa. Meanwhile, external pressure
helps to drive stronger interlayer interaction and results in a higher ratio of
interlayer/intralayer exciton intensity, indicating the enhanced interlayer
exciton behavior. The first-principles calculation reveals the stronger
interlayer interaction which leads to enhanced interlayer exciton behavior in
WS2/MoSe2 heterostructure under external pressure and reveals the robust peak
of interlayer exciton. This work provides an effective strategy to study the
interlayer interaction in vdW heterostructures, which could be of great
importance for the material and device design in various similar quantum
systems.
