Observation of the Phonon Splitting Associated with Strong Interlayered Interaction in Black Phosphorus Structured Polymeric Nitrogen

The discovery of black phosphorus structured polymeric nitrogen (BP-N) under experimental conditions involving a pressure of 126–140 GPa and a temperature of T ∼ 2300 K has attracted significant attention and reaffirms the significance of isostructural transformations at high pressures. BP-N has promising perspectives not only as a potential high-energy-density material (HEDM) but also owing to its exotic properties stemming from its quasi-two-dimensional structure. In this study, the abnormal behavior of phonons in BP-N at different pressures is experimentally and theoretically investigated by employing high-pressure Raman spectroscopy and first-principle calculations. The Raman spectroscopy observations show that the related vibrational modes display a pronounced symmetry breaking and splitting in BP-N with the change of pressure. Theoretical simulations in uniaxial strain effects confirm that the splitting in the phonon branches of BP-N arises from the additional components of stress-induced phonon associated with the interlayer interaction. These results offer valuable insights into the lattice dynamics of BP-N under extreme conditions, also providing new perspectives for the design and engineering of phonons in two-dimensional structures.