Quasiperiodic Sn layer

Quasicrystalline materials exhibit aperiodic long range order and forbidden rotational symmetries, but show sharp diffraction spots. Although quasicrystals were discovered more than 30 years ago, elemental quasicrystals have remained elusive so far. Here, we demonstrate unique characteristics of an elemental Sn layer: it adopts a buckled five-fold quasiperiodic (QP) structure that is different from the icosahedral ($i$)-Al-Pd-Mn substrate. The pseudogap in the electronic states around the Fermi level that stabilizes a quasicrystal, is further deepened in the Sn layer compared to the substrate. On the basis of density functional theory, we relate this intriguing observation to the buckling with enhanced covalency and $sp^3$ bonding between Sn atoms. Quasiperiodicity is observed up to 1.4 nm (5 ML) at 100 K, a thickness regime where the influence of the substrate potential is negligible.