Half-Ice, Half-Fire Driven Ultranarrow Phase Crossover in 1D Decorated q-State Potts Ferrimagnets: An AI-Co-Led Discovery

OpenAI's reasoning model o3-mini-high was used to carry out an exact analytic study of one-dimensional ferrimagnetic decorated $q$-state Potts models. We demonstrate that the finite-temperature ultranarrow phase crossover (UNPC), driven by a hidden "half-ice, half-fire" state in the $q=2$ Potts (Ising) model, persists for $q>2$. We identify novel features for $q>2$, including the dome structure in the field-temperature phase diagram and for large $q$ a secondary high-temperature UNPC to the fully disordered paramagnetic state. The ice-fire mechanism of spin flipping can be applied to higher-dimensional Potts models. These results establish a versatile framework for engineering controlled fast state-flipping switches in low-dimensional systems. Our nine-level AI-contribution rating assigns AI the meritorious status of AI-co-led discovery in this work.