--- res: bibo_abstract: - 'Polaritons with directional in-plane propagation and ultralow losses in van der Waals (vdW) crystals promise unprecedented manipulation of light at the nanoscale. However, these polaritons present a crucial limitation: their directional propagation is intrinsically determined by the crystal structure of the host material, imposing forbidden directions of propagation. Here, we demonstrate that directional polaritons (in-plane hyperbolic phonon polaritons) in a vdW crystal (α-phase molybdenum trioxide) can be directed along forbidden directions by inducing an optical topological transition, which emerges when the slab is placed on a substrate with a given negative permittivity (4H–silicon carbide). By visualizing the transition in real space, we observe exotic polaritonic states between mutually orthogonal hyperbolic regimes, which unveil the topological origin of the transition: a gap opening in the dispersion. This work provides insights into optical topological transitions in vdW crystals, which introduce a route to direct light at the nanoscale.@eng' bibo_authorlist: - foaf_Person: foaf_givenName: J. foaf_name: Duan, J. foaf_surname: Duan - foaf_Person: foaf_givenName: G. foaf_name: Álvarez-Pérez, G. foaf_surname: Álvarez-Pérez - foaf_Person: foaf_givenName: K. V. foaf_name: Voronin, K. V. foaf_surname: Voronin - foaf_Person: foaf_givenName: Ivan foaf_name: Prieto Gonzalez, Ivan foaf_surname: Prieto Gonzalez foaf_workInfoHomepage: http://www.librecat.org/personId=2A307FE2-F248-11E8-B48F-1D18A9856A87 orcid: 0000-0002-7370-5357 - foaf_Person: foaf_givenName: J. foaf_name: Taboada-Gutiérrez, J. foaf_surname: Taboada-Gutiérrez - foaf_Person: foaf_givenName: V. S. foaf_name: Volkov, V. S. foaf_surname: Volkov - foaf_Person: foaf_givenName: J. foaf_name: Martín-Sánchez, J. foaf_surname: Martín-Sánchez - foaf_Person: foaf_givenName: A. Y. foaf_name: Nikitin, A. Y. foaf_surname: Nikitin - foaf_Person: foaf_givenName: P. foaf_name: Alonso-González, P. foaf_surname: Alonso-González bibo_doi: 10.1126/sciadv.abf2690 bibo_issue: '14' bibo_volume: 7 dct_date: 2021^xs_gYear dct_identifier: - UT:000636455600027 dct_isPartOf: - http://id.crossref.org/issn/23752548 dct_language: eng dct_publisher: AAAS@ dct_title: Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition@ fabio_hasPubmedId: '33811076' ...