Topological nature of higher-order hinge states revealed by spin transport

One-dimensional(1D)gapless hinge states are predicated in the three-dimensional(3D)higher-order topological insulators and topological semimetals,because of the higher-order bulk-boundary correspondence.Nevertheless,the topologically protected property of the hinge states is still not demonstrated so far,because it is not accessible by conventional methods,such as spectroscopy experiments and quantum oscillations.Here,we reveal the topological nature of hinge states in the higher-order topological semimetal Cd;As;nanoplate through spin potentiometric measurements.The results of current induced spin polarization indicate that the spin-momentum locking of the higher-order hinge state is similar to that of the quantum spin Hall state,showing the helical characteristics.The spin-polarized hinge states are robust up to room temperature and can nonlocally diffuse a long distance larger than 5μm,further indicating their immunity protected by topology.Our work deepens the understanding of transport properties of the higher-order topological materials and should be valuable for future electronic and spintronic applications.

A Bionic Approach for Topology Optimization for Tension-only or Compression-only Design

A new bionic approach is presented to find the optimal topologies of a structure with tension-only or compression-onlymaterial based on bone remodelling theory.By traditional methods,the computational cost of topology optimization of thestructure is high due to material nonlinearity.To improve the efficiency of optimization,the reference-interval with material-replacement method is presented.In the method,firstly,the optimization process of a structure is considered as bone remodellingprocess under the same loading conditions.A reference interval of Strain Energy Density (SED),corresponding to thedead zone or lazy zone in bone mechanics,is adopted to control the update of the design variables.Secondly,a material-replacement scheme is used to simplify the Finite Element Analysis (FEA) of structure in optimization.In the operation ofmaterial-replacement,the original tension-only or compression-only material in design domain is replaced with a new isotropicmaterial and the Effective Strain Energy Density (ESED) of each element can be obtained.Finally,the update of design variablesis determined by comparing the local ESED and the current reference interval of SED,e.g.,the increment of a relativedensity is nonzero if the local ESED is out of the current reference interval.Numerical results validate the method.