Spin Mixing Control of Interlayer Excitons in ZrS2/ZrNCl Heterostructures

Two-dimensional (2D) transition metal dichalcogenide heterostructures provide a fruitful platform for realizing interlayer excitons (IXs) with spatial separation between the charges. When Janus layers stack into the heterostructures, an extra electric field is introduced to manipulate the properties of the IXs. Here, we demonstrate how the intrinsic electric field of the Janus monolayer ZrNCl affects the IXs in the ZrS2/ZrNCl heterostructures via GW-BSE calculations. Our findings show that both stacking orders 1-S/N and 2-S/Cl with different interfaces exhibit tightly bound bright IXs. Additionally, the dominant excitonic absorption peak arising from interlayer excitation of 1-S/N is located in the infrared range, whereas it is in the visible range in 2-S/Cl. The radiative lifetime of IXs can also be tuned from 10–4 to 10–8 s at 300 K by the stacking order. By analyzing the spin properties, we find that the lowest-energy exciton IX0 of 1-S/N mixes much more spin-singlet states than that of 2-S/Cl and thus has a shorter lifetime. However, for bright exciton IXB, the dominant transition process in 1-S/N is spin-forbidden but dipole-allowed, while it is spin- and dipole-allowed in 2-S/Cl; therefore, the lifetime of bright excitons in 2-S/Cl is shorter than that of 1-S/N. Interestingly, the multiband transition characteristic of IXs in ZrS2/ZrNCl arising from the high energy degeneracy is favorable for satisfying dipole transition selection rules. Our study demonstrates the significance of the degree of mixing of spin-singlet and spin-triplet states, combined with the multiband transition feature, to the lifetime of IX by altering the stacking order of the heterostructures with the Janus layer.