Abstract:

Narrowband terahertz (THz) radiation is crucial for high-resolution spectral identification, but a narrowband THz source driven by a femtosecond (fs) laser has remained scarce. Here, it is computationally predicted that a metal/dielectric/magnetoelastic heterostructure enables converting a fs laser pulse into a multicycle THz pulse with a narrow linewidth down to ∼1.5 GHz, which is in contrast to the single-cycle, broadband THz pulse from the existing fs-laser-excited emitters. It is shown that such narrowband THz pulse originates from the excitation and long-distance transport of THz spin waves in the magnetoelastic film, which can be enabled by a short strain pulse obtained from fs laser irradiation of the metal film when the thicknesses of the metal and magnetoelastic films both fall into a specific range. These results therefore reveal an approach to achieving optical generation of narrowband THz pulse based on heterostructure design, which also has implications in the design of THz magnonic devices.

Full text available from ACS Publications

Abstract:

“Solid-state hydrogen gating of a ferrimagnetic metal enables independent reversal of Néel and magnetization vectors by an electric field.”

Full text available from: Nature Nanotechnology

Abstract:

“Memristors have emerged as transformative devices to enable neuromorphic and in-memory computing, where success requires the identification and development of materials that can overcome challenges in retention and device variability. Here, high-entropy oxide composed of Zr, Hf, Nb, Ta, Mo, and W oxides is first demonstrated as a switching material for valence change memory. This multielement oxide material provides uniform distribution and higher concentration of oxygen vacancies, limiting the stochastic behavior in resistive switching. (Zr, Hf, Nb, Ta, Mo, W) high-entropy-oxide-based memristors manifest the “cocktail effect,” exhibiting comparable retention with HfO₂– or Ta₂O₅-based memristors while also demonstrating the gradual conductance modulation observed in WO₃-based memristors. The electrical characterization of these high-entropy-oxide-based memristors demonstrates forming-free operation, low device and cycle variability, gradual conductance modulation, 6-bit operation, and long retention which are promising for neuromorphic applications.”

Full text available from: Advanced Electronic Materials

ABSTRACT

Ultrawide-band-gap (UWBG) semiconductors are promising for fast, compact, and energy-efficient power-electronics devices. Their wider band gaps result in higher breakdown electric fields that enable high-power switching with a lower energy loss. Yet, the leading UWBG semiconductors suffer from intrinsic materials’ limitations with regard to their doping asymmetry that impedes their adoption in CMOS technology. Improvements in the ambipolar doping of UWBG materials will enable a wider range of applications in power electronics as well as deep-UV optoelectronics. These advances can be accomplished through theoretical insights on the limitations of current UWBG materials coupled with the computational prediction and experimental demonstration of alternative UWBG semiconductor materials with improved doping and transport properties. As an example, we discuss the case of rutile GeO₂ (r-GeO₂), a water-insoluble GeO₂ polytype, which is theoretically predicted to combine an ultra-wide gap with ambipolar dopability, high carrier mobilities, and a higher thermal conductivity than β-Ga₂O₃. The subsequent realization of single-crystalline r-GeO₂ thin films by molecular beam epitaxy provides the opportunity to realize r-GeO₂ for electronic applications. Future efforts toward the predictive discovery and design of new UWBG semiconductors include advances in first-principles theory and high-performance computing software, as well as the demonstration of controlled doping in high-quality thin films with lower dislocation densities and optimized film properties.

Full text available from Applied Physics Letters 

We report on the demonstration of ferroelectricity in Sc_xAl_1-xN grown by molecular beam epitaxy on GaN templates. Distinct polarization switching is unambiguously observed for ScxAl1-xN films with Sc contents in the range of 0.14–0.36. Sc_0.20Al_0.80N, which is nearly lattice- matched with GaN, exhibiting a coercive field of ~ 4.2 MV/cm at 10 kHz and a remnant polarization of ~ 135 uC/cm2. After electrical poling, Sc_0.20Al_0.80N presents a polarization retention time beyond 10⁵ s. No obvious fatigue behavior can be found with up to 3 x 10⁵ switching cycles. The work reported here is more than a technical achievement. The realization of ferroelectric single-crystalline III–V semiconductors by molecular beam epitaxy promises a thickness scaling into the nanometer regime and makes it possible to integrate high-performance fer- roelectric functionality with well-established semiconductor platforms for a broad range of electronic, optoelectronic, and photonic device applications.

Full text available from Applied Physics Letters