Reversible layered/non-layered phase transition in a topological semimetal

The essence of phase transition is symmetry breaking according to Landau’s theory, which serves as a fundamental spatial metric to shape materials’ structures and facilitate the discovery of emergent quantum phases. However, isocompositional phase transitions between layered and non-layered structures are typically restricted to the same bonding network due to the significant differences in surface energies and out-of-plane chemical bonds. Here, we demonstrate a reversible phase transition between layered and non-layered phases in the semimetal PtBi₂, where two phases exhibit diverse structural and physical properties in terms of atomic bonding types and topological properties. Reversible resistance hysteresis loops are revealed in the electrical measurements, which originate from the layered/non-layered phase transition based on the mechanism of intralayer splitting and interlayer reconstructions. Theoretical calculations further support that the interfacial phase transition not only produces a layered/non-layered structural change, but also structure-dependent topological invariants, establishing layered/non-layered phase engineering as a platform for exploring topological and functional quantum states.