  Topologically nontrivial systems can be protected by band topology in
momentum space, as seen in topological insulators and semimetals, or real-space
topology, such as in lattice deformations known as topological disclinations
(TDs). TDs, with inherent chiral symmetry, can support localized states pinned
spectrally to the middle of the topological gap, preventing hybridization with
bulk bands, and making them promising for topological lasers. Here, we
experimentally realize a C4v symmetric TD laser based on perovskite
exciton-polariton lattices at room temperature. Protected by the chiral and
point group symmetries of the lattice, the TD state emerges in the middle of
the gap and at the core of the perovskite lattice. Under a non-resonant pulsed
excitation, coherent polariton lasing occurs precisely at the TD state with a
low threshold of 9.5 uJ/cm2, as confirmed by momentum space and real space
spectra measurements. This study not only introduces a class of
symmetry-protected topological lasers, but also expands the landscape for
exploring exciton-polariton light-matter interactions with novel topological
structures.
