Non-destructive probing of Brillouin-zone-edge phonons in van der Waals heterostructure

Brillouin-zone-edge phonons are of great significance to many-body interactions and intervalley dynamics in two-dimensional (2D) materials. However, probing these elusive modes typically relies on destructive defect engineering for relaxing fundamental momentum conservation. Here, we establish a non-destructive and tunable paradigm by constructing a van der Waals heterostructure of few-layer MnPS₃ and monolayer WSe₂, which induces the emergence of giant anomalous Raman responses from large-momentum phonons from the intact WSe₂ lattice. Based on comprehensive spectroscopic investigations, we propose a phenomenological framework suggesting that this phenomenon is driven by a synergistic structural-electronic mechanism. We postulate that the massive lattice mismatch between few-layer MnPS₃ and monolayer WSe₂ creates a highly incommensurate interface, which provides necessary momentum compensation. Meanwhile, we suppose that the highly localized Mn 3d flat band acts as an energy-matched resonant amplifier. Crucially, we demonstrate the potential tunability of this system through the h-BN spacer insertion and elemental substitutions (FePS₃ and NiPS₃). These manipulations corroborate our hypothesis, allowing modulation of the anomalous responses from giant amplification to complete suppression via deliberate energy detuning. The ability to probe and modulate these fundamental mediators of many-body interactions in a non-destructively way establishes a robust framework for developing advanced 2D quantum phononic architectures.