Near-field nano-spectroscopy of strong mode coupling in phonon-polaritonic crystals - Hu,X; Lo,TW; Mancini,A; Gubbin,CR; Martini,F; Zhang,J; Gong,Z; Politi,A; De,Liberato S; Zhang,X; Lei,D; Maier,SA (APPLIED PHYSICS REVIEWS, 2022)