Topological states in quasicrystals

With the rapid development of topological states in crystals, the study of topological states has been extended to quasicrystals in recent years. In this review, we summarize the recent progress of topological states in quasicrystals, particularly focusing on one-dimensional (1D) and 2D systems. We first give a brief introduction to quasicrystalline structures. Then, we discuss topological phases in 1D quasicrystals where the topological nature is attributed to the synthetic dimensions associated with the quasiperiodic order of quasicrystals. We further present the generalization of various types of crystalline topological states to 2D quasicrystals, where real-space expressions of corresponding topological invariants are introduced due to the lack of translational symmetry in quasicrystals. Finally, since quasicrystals possess forbidden symmetries in crystals such as five-fold and eight-fold rotation, we provide an overview of unique quasicrystalline symmetry-protected topological states without crystalline counterpart.

Two-dimensional Stiefel-Whitney insulators in liganded Xenes

Two-dimensional(2D)Stiefel-Whitney insulator(SWI),which is characterized by the second Stiefel-Whitney class,is a class of topological phases with zero Berry curvature.As an intriguing topological state,it has been well studied in theory but seldom realized in realistic materials.Here we propose that a large class of liganded Xenes,i.e.,hydrogenated and halogenated 2D group-IV honeycomb lattices,are 2D SWIs.The nontrivial topology of liganded Xenes is identified by the bulk topological invariant and the existence of protected corner states.Moreover,the large and tunable bandgap(up to 3.5 eV)of liganded Xenes will facilitate the experimental characterization of the 2D SWI phase.Our findings not only provide abundant realistic material candidates that are experimentally feasible but also draw more fundamental research interest towards the topological physics associated with Stiefel-Whitney class in the absence of Berry curvature.

Reduced conductivity in sandwich-structured BFT@DA/PVDF flexible nanocomposites for high energy storage density in lower electric field

The Ba(Fe_(0.5)Ta_(0.5))O_(3)@DA/PVDF flexible composite films with sandwich-structured are prepared by solution-casting method.According to SEM image,the thickness of the composite film is about 15 mm and the each layer is about 5 mm.The sandwich-structured nanocomposite films not only have higher permittivity but also lower AC conductivity.The high permittivity is due to the large permittivity of BFT and the enhanced interface polarization between ceramic particles and polymer matrix.The low AC conductivity is due to the absence of conductive pathways in the PVDF layer.At low electric field strength of 150 MV/m,the energy density of sandwich-structure composite films filled with 1 vol% is 1.93 J/cm^(3).When the breakdown strength is 250 MV/m,the maximum energy storage density is increased to 4.87 J/cm^(3).The sandwich-structure Ba(Fe_(0.5)Ta_(0.5))O_(3)@DA/PVDF flexible composite films with outstanding energy storage properties in lower electric field can be used for wearable devices in the future.