Influence of interlayer stacking on optical behavior in WSe 2 / MoS 2 van der Waals heterostructures

We investigate the impact of crystal alignment on excitonic behavior in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi>WSe</a:mi> <a:mn>2</a:mn> </a:msub> <a:mo>/</a:mo> <a:msub> <a:mi>MoS</a:mi> <a:mn>2</a:mn> </a:msub> </a:mrow> </a:math> van der Waals heterostructures by comparing eclipsed (AA) and staggered (AB) stacking configurations. Our first-principles and symmetry-based analysis reveal that interlayer stacking symmetry plays a central role in determining the nature of electron-hole pairs. We uncover a rich variety of excitonic states, including spatially confined two-dimensional (2D) excitons, delocalized three-dimensional (3D) excitons, and charge-transfer (CT) excitons with interlayer character. The dimensionality and optical activity of these excitons are governed by the interplay among orbital character, interlayer hybridization, and symmetry-imposed selection rules. Our findings establish general principles for engineering excitonic properties in van der Waals heterostructures through controlled layer orientation and stacking order.