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The advancement of acoustic metamaterials enables the highly efficient absorption of low-frequency noise with a subwavelength structure thickness, but the complexity of these structures often hinders their large-scale practical applications. Here, we propose a straightforward and compact acoustic metamaterial structure composed of Helmholtz resonators with side slits (HRSS) for low-frequency noise absorption. The introduction of side slits not only simplifies the overall structure but also allows for easy adjustment of acoustic characteristics. By adjusting the depth of the resonator within the slit across 25 distinct units, an absorption coefficient above 0.8 is realized from 470 to 930 Hz. This work demonstrates the extensive low-frequency sound absorption capability of HRSS, providing valuable insights into the design of future practical acoustic materials. [ABSTRACT FROM AUTHOR]

Wide bandgap β-Ga2O3 is an ideal candidate material with broad application prospects for power electronic components in the future. Aiming at the application requirements of β-Ga2O3 in space photoelectric devices, this work studies the influence of 40 MeV Si ion irradiation on the microstructure and optical properties of β-Ga2O3 epi-wafers. Raman spectroscopy analysis confirms that Si ion irradiation destroys the symmetric stretching mode of tetrahedral–octahedral chains in β-Ga2O3 epi-wafers, and the obtained experimental evidence of irradiation leads to the enhanced defect density of VO and VGa–VO from x-ray photoelectron spectroscopy. Combined with first-principles calculations, we conclude that most configurations of VO and VGa–VO are likely non-radiative, leading to quenching of experimental photoluminescence intensity. Unraveling optical degradation mechanism and predicting the optical application of β-Ga2O3 devices in the space environment by combining ground irradiation experiments with first-principles calculations still be one of the focuses of research in the future. [ABSTRACT FROM AUTHOR]

Electron traps in AlGaN/GaN high electron mobility transistors were studied by combining theoretical and experimental methods. Energy levels about EC-0.9 eV due to irradiation are identified by deep-level transient spectroscopy (DLTS). Two electron traps, H1 (EC-0.63 eV) and H2 (EC-0.9 eV), were observed in the DLTS spectra. H1 was produced in device or material manufacturing, and H2 was caused by displacement damage. First, we reported that the signal peak of H2 can contribute from three defects labeled H2-1, H2-2, and H2-3 with energies EC-0.77 eV, EC-0.9 eV, and EC-0.98 eV, respectively. According to defect migration temperature and first principles calculation results, it is found that different configurations of di-nitrogen vacancy structures are the source of EC-0.77 eV and EC-0.9 eV signals. The defect of EC-0.98 eV is more stable at high temperatures, which may be related to gallium vacancy. [ABSTRACT FROM AUTHOR]

In this Letter, a bilayer elastic C6v structure is proposed and used to precisely manipulate two topological nontrivial valley pseudo-spin states. According to the theoretical simulation results, the two elastic pseudo-spin states have opposite valley polarizations along propagation directions. Owing to the interlayer polarization and mixing effects of the elastic valley pseudo-spin states in the bilayer elastic C6v structure, the transport and prohibition of elastic valley pseudo-spin states and even the tunneling between layers are flexibly manipulated. The transmission efficiency of elastic valley pseudo-spin states across layers reaches 93%, which has also been confirmed in experiments by the laser ultrasonic method. The in-depth exploration of valley pseudo-spin states with layer indices further expands and enriches the research of valley pseudo-spin states in the elastic environment and lays the foundation for the further design of elastic topological devices. [ABSTRACT FROM AUTHOR]

We demonstrate the direct generation of optical vortex pulses with stable energy and changeable orbital angular momentum. Single Laguerre-Gaussian (LG0,l) laser modes were directly generated using a laser diode with output intensity profile of doughnut distribution. With passive Q-switching, vortex pulses with stable energy were obtained. Moreover, the topological charge was changeable by variation of the pump power. By a mode-converter and second harmonic generation, the LG0,2l mode was identified. It can be proposed that this pulsed laser should have promising applications in various fields based on its compact structure, stable and high pulse energy, and changeable orbital angular momentum. [ABSTRACT FROM AUTHOR]