Heimig, ConnorConnorHeimigAntonov, Alexander A.Alexander A.AntonovGryb, DmytroDmytroGrybPossmayer, ThomasThomasPossmayerWeber, ThomasThomasWeberHirler, MichaelMichaelHirlerBiechteler, JonasJonasBiechtelerSortino, LucaLucaSortinoMenezes, Leonardo de S.Leonardo de S.MenezesMaier, Stefan A.Stefan A.MaierGorkunov, Maxim V.Maxim V.GorkunovKivshar, YuriYuriKivsharTittl, AndreasAndreasTittl2026-06-022026-06-022026-03-27Science Advances 12 (13): eaeb5631 (2026)https://hdl.handle.net/11420/63330Chiral optical cavities are crucial for the development of nonequilibrium quantum materials by discriminating and selectively coupling to light of a specific circular polarization, but fundamentally cannot be realized with conventional mirror cavities. Here, we demonstrate this unique functionality by developing a monolithic transition metal dichalcogenide (TMDC) metasurface with broken out-of-plane symmetry, allowing for the selective formation of self-hybridized chiral exciton-polaritons. Our metasurface maintains maximal chirality for oblique incidence up to 20°, thereby outperforming all previously known designs. Moreover, we study the chiral strong-coupling regime in nonlinear experiments and reveal polaritonic signatures in chiral third-harmonic generation. Our results position maximally chiral van der Waals (vdW) metasurfaces as a versatile platform for tunable chiral polaritonics with applications in nonreciprocal photonic devices and valleytronics.en2375-2548202613Technology::600: TechnologyJournal Article10.1126/sciadv.aeb5631