Intervalley mixing of interface excitons at lateral heterojunctions

Low symmetry of armchair lateral heterojunctions between transition metal dichalcogenide monolayers allows for the mixing of electron states in ${\mathbit{K}}_{+}$ and ${\mathbit{K}}_{\ensuremath{-}}$ valleys. We show that this valley mixing substantially modifies the fine structure and dynamics of electrons and excitons localized at type-II lateral heterojunctions. In particular, it gives rise to the in-plane electron $g$-factor leading to the valley pseudospin precession in the in-plane magnetic field. Also, the interplay of the valley mixing and long-range exchange interaction leads to the magnetically induced linear polarization of exciton photoluminescence along the heterojunction under unpolarized excitation. The degree of polarization can reach $1/3$. From the tight binding model we obtain an analytical expression for the valley coupling constant and estimate it to be as strong as 0.2 eV \AA{} for typical heteropairs.