Phys.org  February 5, 2024 Confinement of light into nanocavities which enhances light–matter interactions generally come at the cost of absorption and low resonator quality factors. An international team of researchers (Israel, USA – Cornell University, Kansas State University, Germany, Spain) suggested an alternative optical multimodal confinement mechanism, unlocking the potential of hyperbolic phonon polaritons in isotopically pure hexagonal boron nitride. They produced deep-subwavelength cavities and demonstrated several orders of magnitude improvement in confinement approaching the intrinsic quality factor of hexagonal boron nitride polaritons. The quality factors they obtained exceeded the maximum predicted by impedance-mismatch considerations indicating that confinement was boosted […]