Science Bulletin最新文献

Band topology has emerged as a novel tool for material design across various domains, including photonic and phononic systems, and metamaterials. A prominent model for band topology is the Su-Schrieffer-Heeger (SSH) chain, which reveals topological in-gap states within Bragg-type gaps (BG) formed by periodic modification. Apart from classical BGs, another mechanism for bandgap formation in metamaterials involves strong coupling between local resonances and propagating waves, resulting in a local resonance-induced bandgap (LRG). Previous studies have shown the challenge of topological edge state emergence within the LRG. Here, we reveal that topological edge states can emerge within an LRG by achieving both topological phase and bandgap transitions simultaneously. We describe this using a model of inversion-symmetric extended SSH chains for locally resonant metamaterials. Notably, this topological state can lead to highly localized modes, comparable to a subwavelength unit cell, when it emerges within the LRG. We experimentally demonstrate distinct differences in topologically protected modes-highlighted by wave localization-between the BG and the LRG using locally resonant granule-based metamaterials. Our findings suggest the scope of topological metamaterials may be extended via their bandgap nature.

High-quality quantum dots (QDs) possess superior electroluminescent efficiencies and ultra-narrow emission linewidths are essential for realizing ultra-high definition QD light-emitting diodes (QLEDs). However, the synthesis of such QDs remains challenging. In this study, we present a facile high-temperature successive ion layer adsorption and reaction (HT-SILAR) strategy for the growth of precisely tailored Zn_1-xCd_xSe/ZnSe shells, and the consequent production of high-quality, large-particle, alloyed red CdZnSe/Zn_1-xCd_xSe/ZnSe/ZnS/CdZnS QDs. The transitional Zn_1-xCd_xSe/ZnSe shells serve to effectively suppress heavy hole energy level splitting and weaken the exciton-longitudinal optical phonon coupling of QDs, thus facilitating the formation of highly luminescent QDs with a near-unity photoluminescence quantum yield of 97.8% and narrow emission with a full width at half maximum of 17.1 nm. In addition, the introduction of transitional shells can extend the particle size of QDs to 19.0 nm, which is beneficial for efficient carrier recombination and reduced Joule heating in QD-based LEDs. As a result, the fabricated QLEDs can achieve a record external quantum efficiency of 38.2%, luminance over 120,000 cd m^-2, and exceptional operational stability T₉₅ (tested at 1,000 cd m^-2) of 24,100 h. These findings provide new avenues for synthesizing high-quality QDs with high color purity.

Bound states in the continuum (BICs) are notable in photonics for their infinite Q factors. Perturbed BICs, or quasi-BICs (QBICs), have finite but ultra-high Q factors, enabling external coupling. So far, most studies have focused on the momentum-space properties of BICs and QBICs, with few discussions on their properties in real space. Here, we experimentally demonstrate that QBICs can induce abrupt lateral beam shifts. By applying Brillouin zone folding to a compound grating waveguide, we form a QBIC band where all states become QBICs. When excited at specific incident angles, these QBICs produce sudden lateral beam shifts, rapidly disappearing as frequencies deviate from the QBIC band. Using terahertz imaging, we capture these beam shifts at different incident angles, characterizing the QBIC band. This work offers alternative insights into QBIC behaviors and supports the development of advanced sensors and wavelength division (de) multiplexers.