Twistronics in van der Waals heterostructures enables programmable electronic, vibrational, and nonlinear optical responses through moiré superlattices, but most platforms are assembled from high-symmetry layers, restricting the accessible symmetry landscape. Here, we introduce an intrinsically asymmetric moiré system by fabricating a van der Waals heterobilayer of monolayer WSe2 (D3h group, C3 rotational symmetry) and monolayer Mo0.4W0.6Se2 alloy (P1 group, C1 rotational symmetry) with intrinsically broken rotational symmetry. Using polarization-resolved Raman spectroscopy in combination with second-harmonic generation (SHG) microscopy over the twist-angle range (0°–60°), we track how interlayer coupling, lattice reconstruction, and global symmetry evolve with twist angle, showing that interlayer phonons act as sensitive probes of the moiré length scale and reveal a continuous crossover from strong coupling near 0°/60° to weak coupling approaching ∼30°. Circularly polarized Raman measurements resolve nearly degenerate phonons and uncover a twist-tunable splitting of the in-plane E2g mode of WSe2. Polarization-resolved SHG visualizes twist-driven modulation of the effective point-group symmetry, with polar patterns evolving from sixfold, C3-like to twofold, C1-like lobes, quantitatively captured by a bond angular momentum model. Our results establish the combination of native symmetry breaking and twist engineering as a generic strategy for programming phonon and symmetry landscapes in van der Waals materials, opening a route to designer moiré crystals in which interfacial coupling, nonlinear optics, and correlated quantum degrees of freedom can be co-engineered within a single, twist-tunable architecture.
Zhang et al. (Mon,) studied this question.