So-Dam Sohn, Ja-Young Koo, Chang-Youn Moon, Daejin Eom, Korea Research Institute of Standards and Science, Daejeon, Republic of Korea
Quasiperiodic structural modulations, such as those observed in moiré superlattices of low-dimensional materials, are known to influence charge transport and surface potentials. However, direct experimental realizations in Weyl semimetals remain limited. In this study, we present direct evidence of a self-organized intercalation layer with quasiperiodic order in a WTe_₂ crystal, observed through high-resolution scanning tunneling microscopy (STM). The intercalated structure forms spontaneously during sample preparation involving epoxy resin, which appears to assist in inserting a molecular layer between the van der Waals gaps of the host crystal. The resulting layer exhibits an atomically flat, lamellar architecture composed of alternating high- and low-contrast segments arranged in a quasiperiodic sequence. The sequence follows the Pell number series, associated with the silver mean. Despite long-range ordering, the pattern is locally disrupted by structural imperfections, including missing segments, segment swaps, and phason defects. The typical coherence length of the pattern is around 15 segments. This quasiperiodic modulation acts as a built-in potential on the WTe_₂ surface, leading to enhanced local conductance near the Fermi level while keeping the semimetallic phase intact. This behavior originates from structural modulation rather than chemical changes. Our results provide a rare example of emergent quasiperiodicity in a topological semimetal and demonstrate its direct impact on surface electronic states. These findings point to a structural pathway for tuning interfacial properties in 2D layered systems, with potential relevance for devices that benefit from quasiperiodic potential landscapes.