Abstract
Heterojunctions between two crystalline semiconductor layers or regions can always lead to engineering the electronic energy bands in various devices, including transistors, solar cells, lasers, and organic electronic devices. The performance of these heterojunction devices depends crucially on the band alignments and their bending at the interfaces, which have been investigated for years according to Anderson’s rule, Schottky-Mott rule, Lindhard theory, quantum capacitance, and so on. Here, we demonstrate that by engineering two different acoustic waveguides with forbidden bands, one can achieve an acoustic heterojunction with an extraordinary transmission peak arising in the middle of the former gaps. We experimentally reveal that such a transmission is spatially dependent and disappears for a special junction structure. The junction proximity effect has been realized by manipulating the acoustic impedance ratios, which have been proven to be related to the geometrical (Zak) phases of the bulk bands. Acoustic heterojunctions bring the concepts of quantum physics into the classical waves and the macroscopic scale, opening up the investigations of phononic, photonic, and microwave innovation devices.
Highlights
Heterojunctions refer to the interface regions formed by the contact of two different semiconductors[1,2,3,4,5]
To more clearly identify the junction structure effects, we present the peak frequency vs the length of Waveguide II (WII) in Fig. 2d, where the red circles and the blue squares denote the frequencies of the transmitted peaks for L1 = 23 mm and 33 mm, respectively, and the simulated results are presented by the bold dots connected by the dotted and dashed lines
We have found the heterojunction proximity effects experimentally and theoretically in an elaborated acoustic heterojunction waveguide
Summary
Heterojunctions refer to the interface regions formed by the contact of two different semiconductors[1,2,3,4,5]. Due to the similar band structures as semiconductor materials, the artificial periodic structures, known as metamaterials, have attracted a rapidly growing interest, such as sonic crystals[22], superlens[23,24], negative refraction[25,26], electromagnetic cloaks[27], thermal diodes[28], and acoustic topological materials[29,30,31,32,33] As with their semiconductor counterparts, integrating metamaterials with different band gaps can result in heterojunctions at interfaces, which have already been used in nanophotonics to achieve high performance devices[34] and all-optical memory[35]. The further theoretical and numerical results revealed the mechanism of the junction proximity effects, which would benefit the underlying physics exploration on heterojunction geometries and pave the way for quantum and classical functional devices based on heterojunctions
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