Approaching the forbidden phase transition in one-dimensional Ising models with ultranarrow phase crossover

The rigorous ruling that no phase transition at finite temperature is allowed in one-dimensional (1D) Ising model and quantum Heisenberg model with short-range interactions has fundamentally hindered the exploration of the 1D systems for understanding various phase transitions and critical phenomena, let alone their technology applications. Frustration was found to drive pseudotransition in certain decorated 1D Ising models, which however suffers from the feature that the crossover temperature T₀ goes to zero as the crossover gets narrower. Here, we report that the forbidden transition can be approached arbitrarily closely at fixed finite temperature T₀—either spontaneously or in the presence of a magnetic field—by independently making the crossover width 2δT exponentially narrower and narrower (δT = 0 means a genuine transition), resulting in an ultranarrow phase crossover (UNPC) with large latent heat that would be characterized as a genuine first-order phase transition in a routine laboratory measurement. Furthermore, we show that such UNPC can be implemented in an infinite number of 1D Ising systems, establishing a new paradigm for achieving exact knowledge of various outstanding physical problems and promising application of 1D devices.