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In this paper, a broadband achromatic focusing metasurface design scheme based on the equivalent circuit theory and optimized by a deep learning method is proposed. The designed metasurface element consists of multilayer metal rings and a grounding layer, and the phase modulation effect of achromatic aberration in a wide frequency range is realized by precisely controlling the distance between the layers. The preparation of this complex structure is realized by using additive manufacturing technology, which effectively overcomes the limitations of traditional printed circuit board technology in manufacturing complex structures. To further improve the design efficiency, deep conditional generative adversarial network is introduced in this paper to quickly determine the structural parameters and realize the inverse design, which significantly improves the efficiency and accuracy of the metasurface structure design. The experimental results show that the metasurface possesses good focusing performance in the 17 to 35 GHz band with an effective bandwidth utilization of 69.2 %. The design method proposed in this study combines artificial intelligence and additive manufacturing technology, which provides new design ideas for applications in the fields of communication, optics and wireless energy transmission. 

Abstract One-dimensional chiral interface channels can be created at the boundary of two quantum anomalous Hall (QAH) insulators with different Chern numbers. Such a QAH junction may function as a chiral edge current distributer at zero magnetic field, but its realization remains challenging. Here, by employing an in-situ mechanical mask, we use molecular beam epitaxy to synthesize QAH insulator junctions, in which two QAH insulators with different Chern numbers are connected along a one-dimensional junction. For the junction between Chern numbers of 1 and −1, we observe quantized transport and demonstrate the appearance of the two parallel propagating chiral interface channels along the magnetic domain wall at zero magnetic field. For the junction between Chern numbers of 1 and 2, our quantized transport shows that a single chiral interface channel appears at the interface. Our work lays the foundation for the development of QAH insulator-based electronic and spintronic devices and topological chiral networks. 

Uniaxial strain has been widely used as a powerful tool for investigating and controlling the properties of quantum materials. However, existing strain techniques have so far mostly been limited to use with bulk crystals. Although recent progress has been made in extending the application of strain to two-dimensional van der Waals (vdW) heterostructures, these techniques have been limited to optical characterization and extremely simple electrical device geometries. Here, we report a piezoelectric-based in situ uniaxial strain technique enabling simultaneous electrical transport and optical spectroscopy characterization of dual-gated vdW heterostructure devices. Critically, our technique remains compatible with vdW heterostructure devices of arbitrary complexity fabricated on conventional silicon/silicon dioxide wafer substrates. We demonstrate a large and continuously tunable strain of up to −0.15% at millikelvin temperatures, with larger strain values also likely achievable. We quantify the strain transmission from the silicon wafer to the vdW heterostructure, and further demonstrate the ability of strain to modify the electronic properties of twisted bilayer graphene. Our technique provides a highly versatile new method for exploring the effect of uniaxial strain on both the electrical and optical properties of vdW heterostructures and can be easily extended to include additional characterization techniques.