Anisotropic Γ-Valley Interlayer Excitonic Emission in Anisotropic-Isotropic 2D Heterostructures.

In-plane anisotropy of 2D materials and their heterostructures provides an essential degree of freedom for enabling direction-selective physical responses. However, realizing anisotropic optical responses in interlayer exciton (ILE) of type-II van der Waals heterostructures has remained elusive, as most heterostructures rely on high-symmetry group-VI transition metal dichalcogenides, and attempts to introduce low-symmetry layers are hindered by interlayer momentum mismatch leading to inefficient radiative recombination. Here, we demonstrate anisotropic ILE emission in ReS2/WS2 enabled by Γ-point momentum matching. Polarization-resolved photoluminescence (PL) reveals three distinct ILE peaks, appearing at 1.37-1.42 eV for 1L-ReS2/2L-WS2 and 1.32-1.37 eV for 2L-ReS2/2L-WS2. Time-resolved, power- and temperature-dependent PL measurements, together with first-principles many-body calculations, confirm strongly anisotropic interlayer excitons from a direct Γ-point interlayer bandgap. Furthermore, ILE intensity is independent of excitation polarization due to dominant WS2 absorption, providing a stable exciton supply for exciton transport. These findings position momentum-matched anisotropic-isotropic heterostructures as a platform for polarization-selective optoelectronics and anisotropic excitonics.