Intercalation-induced staging superstructures in K_xNbSe₂

Atomic intercalation has been widely adopted to tune the physical properties, such as superconductivity, in layered van der Waals materials. Unfortunately, for most of the intercalated materials, the structural evolution still remains elusive, particularly at microscopic scale. In this work, we used liquid ammonia method to fabricate a series of K_xNbSe₂samples by intercalating potassium (K) atoms into 2H-NbSe₂single crystal. X-Ray diffraction (XRD) and transmission electron microscopy (TEM) measurements indicated the formation of superstructures that can be well described by a staging model, with various periods ranging from a few layers to ∼50 nm. Accordingly, such intercalation-induced superstructures result in series of stepwise superconductivity transitions. This work provides a direct evidence of the intercalation-induced superstructures and the resultant step-like superconductivity transition in KxNbSe₂.