The basic locus of ramified unitary Shimura varieties of signature $(n-1,1)$ at maximal vertex level

We construct the Bruhat–Tits stratification of the reduced locus of the ramified unitary Rapoport–Zink space of signature $(n-1,1)$, with the level being the stabilizer of a vertex lattice. We develop the local model theory for Bruhat–Tits strata, proving their normality and Cohen–Macaulayness, and provide precise dimension formulas. Additionally, we establish an explicit scheme-theoretical isomorphism between Bruhat–Tits strata and Deligne–Lusztig varieties.