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Acoustic emission, AE, spectroscopy identifies dislocation avalanches and crack propagation in high-purity Cu with self-stabilized dislocation networks. These samples were produced by additive manufacturing where thermal gradients form cellular structures. These structures confine avalanches of dislocation movements (∼confined dislocations) with an energy exponent ε = 1.82 ± 0.04. Free dislocation movement follows force-integrated mean-field behavior with ε = 1.6 ± 0.02. Additional crack propagation under tension exhibits a critical failure exponent of ε = 1.45 ± 0.01. These three mechanisms combine to generate sample failure under tension. We use this example to demonstrate how different avalanche mechanisms can be disentangled in AE spectroscopy of additive manufactured metal and how the specific self-stabilized dislocation networks influence these avalanche dynamics. [ABSTRACT FROM AUTHOR]

We present a report on hybrid InSb–Pb nanowires that combine high spin–orbit coupling with a high critical field and a large superconducting gap. Material characterization indicates the Pb layer of high crystal quality on the nanowire side facets. Hard induced superconducting gaps and gate-tunable supercurrent are observed in the hybrid nanowires. These results showcase the promising potential of this material combination for a diverse range of applications in hybrid quantum transport devices. [ABSTRACT FROM AUTHOR]

The allotrope of carbon, biphenylene, was prepared experimentally recently [Fan et al., Science 372, 852–856 (2021)]. In this Letter, we perform first-principles simulation to understand the bonding nature and structure stability of the possible in-plane heterostructure built by graphene and biphenylene. We found that the graphene–biphenylene in-plane heterostructure only exhibits along the armchair direction, which is connected together by strong covalent bonds and energetically stable. Then, the non-equilibrium molecular dynamics calculations are used to explore the interfacial thermal properties of the graphene/biphenylene heterostructure. It is found that the graphene/biphenylene in-plane heterostructure possesses an excellent interfacial thermal conductance of 2.84 × 109 W·K−1·m−2 at room temperature. Importantly, the interfacial thermal conductance presents different temperature dependence under opposite heat flux direction. This anomalous temperature dependence results in increased thermal rectification ratio with temperature about 40% at 350 K. This work provides comprehensive insight into the graphene–biphenylene heterostructure and suggests a route for designing a thermal rectifier with high efficiency. [ABSTRACT FROM AUTHOR]

In situ neutron diffraction experiments have been performed to investigate the deformation mechanisms on CoCrFeNi high entropy alloys (HEAs) with various amounts of doped Cu. Lattice strain evolution and diffraction peak analysis were used to derive the stacking fault probability, stacking fault energy, and dislocation densities. Such diffraction analyses indirectly uncovered that a lower degree of Cu doping retained the twinning behavior in undoped CoCrFeNi HEAs, while increasing the Cu content increased the Cu clusterings which suppressed twinning and exhibited prominent dislocation strengthening. These results agree with direct observations by transmission electron microscopy. [ABSTRACT FROM AUTHOR]

III–V Indium Arsenide (InAs) nanowire photodetectors have attracted intensive research attention due to their high carrier mobility, direct and narrow bandgap, and nanoscale dimensions, offering immense potential in nanoscale optoelectronics, particularly for applications in photonic integrated circuits. Despite extensive studies on the properties of InAs nanowires, their photoresponse remains intricate, displaying bipolar behavior (i.e., positive and negative photoresponse) within the same device under varying conditions. However, the underlying driving mechanism remains unclear. In this work, we have systematically studied the transition between the negative photoresponse and positive photoresponse in the InAs nanowire photodetector under different conditions. We found the bipolar photoresponse is directly related to the occupation status of the surface trap states, and it could be effectively regulated by the gate voltage, power intensity, as well as the illumination duration. Furthermore, we developed a waveguide-integrated InAs nanowire photodetector using electron photoresist with an optical loss as low as 0.122 dB/μm. This achievement underscores its potential for application in photonic integrated photodetectors, laying the groundwork for future integration of InAs nanowire photodetectors into photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Transformation-induced plasticity (TRIP) high-entropy alloys (HEAs) have drawn great attention as they present excellent mechanical properties, and their phase stability is critical for the underlying deformation mechanisms and the application temperature range. In this study, the kinetic phase transformation behavior of a dual-phase TRIP-HEA Fe50Mn30Co10Cr10 (at. %) was probed by in situ neutron diffraction during thermal cycling between 293 and 425 K. Continuous austenitic and martensitic transformation were visualized through the evolution of hexagonal close-packed phase fraction during thermal cycling. Specifically, thanks to the magnetic sensitivity of neutron diffraction, it was found that the martensitic transformation under cooling became suppressed when the antiferromagnetic ordering started at ∼326 K. This temperature was further confirmed as the Néel temperature by magnetization measurements. Thermodynamic calculations revealed that the suppression effect on martensitic transformation is attributed to the consumption of the chemical driving force by the magnetic ordering. The magnetic ordering at such relatively high temperature is associated with the high Mn content. These findings shed light on a potential strategy to achieve better mechanical properties of Mn-containing alloys by manipulating the magnetic property through tuning the Mn content. [ABSTRACT FROM AUTHOR]

Metal oxide-based memristors usually exhibit robust resistive switching characteristics but poor mechanical tolerance, limiting their applications in wearable intelligent electronics. Here, we report a highly flexible and robust hafnium oxide-based memristor by using the ultrathin substrate for wearable in-memory computing. The fabricated memristor can display reliable resistive switching behaviors, including low switching voltage, good endurance, and excellent uniformity, under an extremely bending state with the radius of 0.8 mm. The mechanical behavior of the flexible memristor with varying substrate thickness is systematically analyzed using the finite element method. Moreover, typical synaptic plasticity including long-term potentiation and long-term depression was verified under the extremely bending state. Based on the highly flexible and robust memristor device, a three-layer neural network was constructed using a software simulator, achieving a recognition accuracy of 90.49% for handwritten digit recognition under the bending state. These results demonstrate our robust memristor synapse shows high mechanical flexibility, paving a promising way to realizing wearable in-memory computing. [ABSTRACT FROM AUTHOR]

We report on electrical gating of superconducting bilayer NbSe2 using dual-gate field-effect transistors constructed by the van der Waals assembly of mechanically exfoliated NbSe2 and SrTiO3 thin films grown by molecular beam epitaxy. Charge carrier doping, but not a pure electric field, was found to induce changes to the superconducting resistive transition, reaching a 190 mK modulation of the critical temperature and excluding the Rashba effect. The phase space for the superconducting state beyond the Pauli limit under in-plane magnetic fields expands when the critical temperature is enhanced. Quantitative comparison with theory suggests the presence of intervalley scattering, which competes with Ising spin–orbit coupling to set the superconducting-normal phase boundary. The gating method demonstrated here may be applied to study other van der Waals layered superconductors. [ABSTRACT FROM AUTHOR]

Thermoelectric materials, based on photo-thermoelectric effect (PTE), may be promising in photo-detection because of their self-power, extremely broad-band, and free of cryogenic attachments. Up to now, the performance of PTE is mainly optimized through enhancement of extrinsic absorption such as using optical metamaterials. Instead, we here improve the PTE through materials engineering, accordingly systematically investigated the PTE of both P- and N-type SnSe crystals with different carrier concentrations (1017–1019 cm−3). P-type SnSe has much better photo-thermoelectric performance than the N-type one. Among P-type SnSe, the SnSe crystal with the largest carrier concentration (∼1019 cm−3 at room temperature) demonstrates the highest photo-thermoelectric performance. Analysis by a modified two-temperature model suggests that the key parameter of enhanced PTE is the high electrical conductivity, which leads to large optical absorption and large temperature difference. Our work provides a guideline on how to engineer thermoelectric materials to enhance their photo-thermoelectric performance. [ABSTRACT FROM AUTHOR]

Here, we report the growth of (Sr, Ca) Nd2Fe2O7 single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 103 Hz in a 1 T magnetic field, can be obtained in a SrNd2Fe2O7 crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and 57Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd2Fe2O7 can be attributed to polaronic hopping between two neighboring Fe3+ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd2Fe2O7 is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd2Fe2O7 crystals at room temperature can be used in magneto-dielectric controlled devices. [ABSTRACT FROM AUTHOR]

It is necessary but challenging to verify topological surface states of α-Sn by electrical transport. In this work, we demonstrate conclusive transport evidence on topological properties of an α-Sn film grown on a CdTe substrate by molecular beam epitaxy. A Berry phase determined from Shubnikov–de Haas oscillations is 0.98π. A two-dimensional (2D) Fermi surface is clearly demonstrated by angle-dependent oscillations. We believe the nontrivial topology originates from the 2D Dirac fermions of the topological surface states. In addition, both anisotropic magneto-resistance and planar Hall effect have negative amplitudes at higher fields, which we attribute to the spin-flip backscattering in the topological surface states. We also show that these topological surface states have a long relaxation time of ∼95 fs, making α-Sn a potential candidate for high-efficiency spintronics. [ABSTRACT FROM AUTHOR]

Sound absorption is important for room acoustics and remediation of noise. Acoustic metamaterials have recently emerged as one of the most promising platforms for sound absorption. However, the working bandwidth is severely limited because of the strong dispersion in the spectrum caused by local resonance. Utilizing the coupling effect among resonators can improve the absorbers' performance, but the requirement of collecting coupling effects among all resonators, not only the nearest-neighbor coupling, makes the system too complex to explore analytically. This Letter describes deep learning based acoustic metamaterials for achieving broadband sound absorption with no visible oscillation in a targeted frequency band. We numerically and experimentally achieve an average absorption coefficient larger than 97% within the ultra-broadband extending from 860 to 8000 Hz, proving the validity of the deep learning based acoustic metamaterials. The excellent ultra-broadband and near-perfect absorption performance allows the absorber for versatile applications in noise-control engineering and room acoustics. Our work also reveals the significance of modulating coupling effects among resonators, and the deep learning approach may blaze a trail in the design strategy of acoustic functional devices. [ABSTRACT FROM AUTHOR]

Hafnium-oxide-based materials are considered a promising candidate for next-generation nonvolatile memory devices owing to their good CMOS compatibility and robust ferroelectricity at the nanoscale. In this work, we synthesize highly (111)-oriented La-doped HfO2 (HLO) ferroelectric thin films via pulsed laser deposition. Furthermore, the effect of La dopant concentration, thickness, and growth temperature on the ferroelectricity of HLO films is investigated in detail. A maximum remnant polarization of ∼9 μC/cm2 is achieved for only the 5-nm-thick 3 mol. % HLO films without a wake-up process. The 180° inversion of the domain, the butterfly-shaped capacitance–voltage curve, and typical ferroelectric displacement current curve further demonstrate the robust ferroelectricity at the nanoscale. Moreover, the phase evolves from the monoclinic to the orthorhombic and subsequently to the cubic phase with increasing La concentration, which is due to the combined action of oxygen vacancy, epitaxial strain, and chemical pressure. Additionally, in the interface configuration of HLO/La0.7Sr0.3MnO3 (LSMO), the MnO20.7− layer is substituted by the HLO layer on the MnO2-terminated surface of LSMO, which can be attributed to the fact that the HLO layer with higher electronegativity replaces the MnO20.7− layer with the same electronegativity in the HLO film. Therefore, this study provides a reliable pathway for directly obtaining a lightly doped HLO ferroelectric thin film, which can help to broaden the understanding of the ferroelectric physical mechanisms with element doping. [ABSTRACT FROM AUTHOR]

Manipulation of carrier types in SnSe crystals is quite advantageous to fabricate SnSe-based homojunction devices such as thermoelectric modules. However, tuning the n-type charge carrier at an optimal level of SnSe is quite challenging because of its natural p-type without intentional doping. Here, we report the realization of the n-type SnSe through halogens or Ce doping. Importantly, heavily electron doped SnSe single crystals (∼1019 cm−3) can be obtained by Ce-doping through the Bridgeman method. The electrical conductivity of as-grown SnSe crystals evolves from thermally activated behavior to the metallic one when the electron concentrations are increased from 1016 to 1019 cm−3. Remarkably, the power-factor and electronic quality factor of heavily electron Ce-doped SnSe crystals can reach 1.59 and 0.44 μW cm−1 K−2 at 300 K, respectively, which is one of the best thermoelectric n-type SnSe. This work suggests that Ce-doping through the Bridgeman method is an ideal route for further improving the thermoelectric property of n-type SnSe crystals. [ABSTRACT FROM AUTHOR]

To explore the bandgap tunability in strain-compensated superlattices, we have grown a series of InAs/AlAs strain-compensated short-period superlattices (SPSs) with different period lengths by molecular beam epitaxy. Although the average indium composition of the InAs/AlAs SPS samples remains the same, the bandgaps of these SPSs measured by photoluminescence show a strong dependence on the period length, ranging from 1.41 to 1.01 eV as the period length varies from 4 ML to 10 ML. This fine control on the period length can extend the cutoff wavelength of this digital-alloy-like InAlAs (lattice matched to InP) material up to 1230 nm at room temperature. Multiple transitions are observed in Fourier transform infrared spectra, which agree well with the calculation and confirm the confinement in this structure. The strain effect in tuning the band structures and the band alignments is demonstrated, showing that longer period length together with smaller conduction band offset has led to the smaller effective bandgap of the InAs/AlAs SPS. [ABSTRACT FROM AUTHOR]