Single-layer Counterparts Research Articles

Advances in Coating Materials for Silicon-Based Lithium-Ion Battery Anodes

Silicon anodes, which exhibit high theoretical capacity and very low operating potential, are promising as anode candidates that can satisfy the conditions currently required for secondary batteries. However, the low conductivity of silicon and the alloying/dealloying phenomena that occur during charging and discharging cause sizeable volume expansion with side reactions; moreover, various electrochemical issues result in inferior cycling performance. Therefore, many strategies have been proposed to mitigate these problems, with the most commonly used method being the use of nanosized silicon. However, this approach leads to another electrochemical limitation—that is, an increase in side reactions due to the large surface area. These problems can effectively be resolved using coating strategies. Therefore, to address the issues faced by silicon anodes in lithium-ion batteries, this review comprehensively discusses various coating materials and the related synthesis methods. In this review, the electrochemical properties of silicon-based anodes are outlined according to the application of various coating materials such as carbon, inorganic (including metal-, metal oxide-, and nitride-based) materials, and polymer. Additionally, double shells introduced using two materials for double coatings exhibit more complementary electrochemical properties than those of their single-layer counterparts. The strategy involving the application of a coating is expected to have a positive effect on the commercialization of silicon-based anodes.

Reducing Off-State and Leakage Currents by Dielectric Permittivity-Graded Stacked Gate Oxides on Trigate FinFETs: A TCAD Study.

Since its invention in the 1960s, one of the most significant evolutions of metal-oxide semiconductor field effect transistors (MOSFETs) would be the 3D version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During recent decades, the width of fin (Wfin) and the neighboring gate oxide width (tox) in FinFETs has shrunk from about 150 nm to a few nanometers. However, both widths seem to have been leveling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting the Penn model and Maxwell-Garnett mixing formula for a dielectric constant (κ) calculation for nanolaminate structures, FinFETs with two- and three-stage κ-graded stacked combinations of gate dielectrics with SiO2, Si3N4, Al2O3, HfO2, La2O3, and TiO2 perform better against the same structures with their single-layer dielectrics counterparts. Based on this, FinFETs simulated with κ-graded gate oxides achieved an off-state drain current (IOFF) reduced down to 6.45 × 10-15 A for the Al2O3: TiO2 combination and a gate leakage current (IG) reaching down to 2.04 × 10-11 A for the Al2O3: HfO2: La2O3 combination. While our findings push the individual dielectric laminates to the sub 1 nm limit, the effects of dielectric permittivity matching and κ-grading for gate oxides remain to have the potential to shed light on the next generation of nanoelectronics for higher integration and lower power consumption opportunities.

Mechanical and piezoresistive performance of additively manufactured carbon fiber/PA12 hybrid honeycombs

This study investigates a novel self-sensing honeycomb composite structure composed of two distinct cellular layers with differing unit cell architectures, specifically hexagonal and re-entrant designs. Short carbon fiber (CF)/polyamide 12 (PA12) composite filaments with 0, 5 or 15 wt.% CF content were utilized to additively manufacture the honeycomb structures via Fused Filament Fabrication (FFF), and their mechanical and piezoresistive self-sensing characteristics were experimentally investigated under quasi-static in-plane and out-of-plane compression at both room temperature and elevated temperatures. The results reveal that the hybrid hexagonal/re-entrant (HR) honeycombs mechanically outperform their non-hybrid double-layer and single-layer counterparts under in-plane loading, reporting an increase in collapse strength and energy absorption by factors of 1.64 and 2.25, respectively. These improvements are attributed to the mechanical interactions occurring at the interface between the auxetic and non-auxetic layers within the hybrid structure, effectively enhancing its structural attributes. Furthermore, the double-layer honeycombs display excellent strain-sensing capabilities within the elastic regime, with gauge factors reaching values as high as 146. Mechanical tests conducted at elevated temperatures reveal that the CF/PA12 honeycombs retain a significant portion of their elastic modulus, strength and energy absorption even at 125 °C, while maintaining high gauge factors of up to 72.4. These honeycombs also exhibit pronounced thermoresistive behavior, evidenced by a decrease in electrical resistance of up to 41.3 % with increasing temperatures from 25 to 125 °C. Considering their exceptional combination of thermo-mechanical, thermoresistive and piezoresistive characteristics, these hybrid double-layered CF/PA12 honeycombs hold promise for potential applications in multifunctional lightweight structures, offering integrated temperature and strain-sensing capabilities.

Effect of interlayer exchange coupling interaction on topological phase of a bilayer honeycomb Heisenberg ferromagnet

Layered magnetic topological materials are material systems that exhibit both magnetic ordering and topological properties in their smallest two-dimensional units. Studying these systems may lead to the observation of new physical properties and phenomena, which has attracted considerable attention from researchers. The effect of interlayer exchange coupling interactions on bilayer honeycomb Heisenberg ferromagnets with interlayer coupled topological phase is investigated by using linear spin wave theory. The influence of introducing two additional types of interactions, i.e. interlayer exchange coupling interaction and interlayer easy-axis anisotropy interaction, on the topological phase transition are also explored in this work. By calculating the magnon dispersion relations at various interlayer exchange coupling interaction intensities, it is found that the band gaps of high energy band and low energy band both close and reopen at the Dirac points when the system reaches the critical value of interlayer exchange coupling interaction. In magnon systems, such physical phenomena typically relate to topological phase transitions. When calculating the Berry curvature and Chern numbers for the bands in the aforementioned process, it is found that the sign of the Berry curvature reverses and the Chern numbers change when the critical value of interlayer exchange coupling interaction strength is reached, confirming that a topological phase transition occurs indeed. Introducing two other types of interlayer exchange coupling interactions in this process can lead various novel topological phases to occur in the system. The enhancement of interlayer easy-axis anisotropy interactions is likely to impede the topological phase transitions occurring in the system. We find that a major distinction between bilayer honeycomb ferromagnets and their single-layer counterparts lies in the fact that during a topological phase transition, the sign of the magnon thermal Hall coefficient does not change; on the contrary, abrupt shift in the thermal Hall coefficient curve occurs which can be seen as an indicator of topological phase transition of bilayer honeycomb ferromagnets, and is also reflected in the change in magnon Nernst coefficient. The research results of this work can provide theoretical support for developing novel spintronic devices with enhanced information transmission capabilities by using bilayer honeycomb ferromagnetic materials, and can also provide theoretical reference for studing other bilayer ferromagnetic systems.

Bilayer hydrogel with a protective film and a regenerative hydrogel for effective diabetic wound treatment.

Diabetic foot ulcers (DFUs) are one of the most serious complications of diabetes, often leading to necrosis and amputation. DFU is caused by the intricate diabetic microenvironment, including ischemia, hypoxia, hyperinflammation, reduced angiogenesis, and persistent infection. Traditional wound dressings made of single or mixed materials often struggle to meet all the requirements for effective diabetic wound healing. In contrast, multilayer dressings comprising more than single layers have the potential to address these challenges by combining their diverse chemical and physical properties. In this study, we developed a bilayer hydrogel comprising a GelMA-ALG-nano-ZnO protective film and a COL1-PRP regenerative hydrogel for facilitating diabetic wound healing. We demonstrated the protective properties against bacterial infection of the protective film, while highlighting the regenerative potential of the COL1-PRP hydrogel in promoting fibroblast and MUVEC migration, extracellular matrix secretion and deposition, and angiogenesis. Importantly, the bilayer hydrogel exhibited superior efficacy in promoting full-thickness wound healing in a diabetic rat model compared to its single-layer hydrogel counterparts. This multi-layer approach offers a promising strategy for addressing the complexities of diabetic foot treatment and improving clinical outcomes.

Morphological, thermo-mechanical, and barrier properties of coextruded multilayer polylactide composite films reinforced with graphene nanoplatelets and encapsulated thyme essential oil

The food industry has been looking for biodegradable active packaging film, which has a lower environmental footprint and can extend shelf-life. This work aimed to develop a polylactide-based antibacterial nanopackaging with a tri-layer structure. This coextruded tri-layer film was composed of an internal extruded layer of polylactide (PLA), a central layer of PLA loaded with encapsulated thyme essential oil, and an outer layer of PLA with graphene nanoplatelets. The tri-layer packaging films' morphological, rheological, thermal, barrier, and antibacterial properties were evaluated and compared to those of their single-layer counterparts. Dispersion of nanoparticles in PLA matrix or in composites is described by rheological, thermal, and XRD analysis. The multilayer films displayed some roughness on the surface, and heterogeneity can be seen through phase imaging compared to single-layer films. Antibacterial assays of the film confirmed a strong bactericidal effect against gram-positive and gram-negative bacteria, maintaining this activity for 21 days.

Stacked Intelligent Metasurfaces for Efficient Holographic MIMO Communications in 6G

A revolutionary technology relying on Stacked Intelligent Metasurfaces (SIM) is capable of carrying out advanced signal processing directly in the native electromagnetic (EM) wave regime. An SIM is fabricated by a sophisticated amalgam of multiple stacked metasurface layers, which may outperform its single-layer metasurface counterparts, such as reconfigurable intelligent surfaces (RIS) and metasurface lenses. We harness this new SIM for implementing holographic multiple-input multiple-output (HMIMO) communications without requiring excessive radio-frequency (RF) chains, which is a substantial benefit compared to existing implementations. First of all, we propose an HMIMO communication system based on a pair of SIM at the transmitter (TX) and receiver (RX), respectively. In sharp contrast to the conventional MIMO designs, SIM is capable of automatically accomplishing transmit precoding and receiver combining, as the EM waves propagate through them. As such, each spatial stream can be directly radiated and recovered from the corresponding transmit and receive port. Secondly, we formulate the problem of minimizing the error between the actual end-to-end channel matrix and the target diagonal one, representing a flawless interference-free system of parallel subchannels. This is achieved by jointly optimizing the phase shifts associated with all the metasurface layers of both the TX-SIM and RX-SIM. We then design a gradient descent algorithm to solve the resultant non-convex problem. Furthermore, we theoretically analyze the HMIMO channel capacity bound and provide some fundamental insights. Finally, extensive simulation results are provided for characterizing our SIM-aided HMIMO system, which quantifies its substantial performance benefits, e.g., 150% capacity improvement over both conventional MIMO and its RIS-aided counterparts.

The benefit of Ca in improving pinning of BaZrO3-Y2O3 doubly-doped YBa2Cu3O7-x/Ca0.3Y0.7Ba2Cu3O7-x multilayer nanocomposite films

This work examines the pinning enhancement in BaZrO 3 (BZO) +Y2O3 doubly-doped (DD) YBa2Cu3O7 (YBCO) nanocomposite multilayer (DD-ML) films. The film consists of two 10 nm thin Ca0.3Y0.7Ba2Cu3O7-x (CaY-123) spacers stacking alternatively with three BZO + Y2O3/YBCO layers of 50 nm each in thickness that contain 3 vol% of Y2O3 and BZO doping in the range of 2–6 vol%. Enhanced magnetic vortex pinning and improved pinning isotropy with respect to the orientation of magnetic field (B) have been achieved in the DD-ML samples at lower BZO doping as compared to that in the single-layer counterparts (DD-SL) without the CaY-123 spacers. For example, the pinning force density (F p ) of ∼58 GNm−3 in 2 vol.% of DD-ML film is ∼110% higher than in 2 vol% of DD-SL at 65 K and B//c-axis, which is attributed to the improved pinning efficiency by c-axis aligned BZO nanorods through diffusion of Calcium (Ca) along the tensile-strained channels at BZO nanorods/YBCO interface for improvement of the interface microstructure and hence pinning efficiency of BZO nanorods. An additional benefit is in the considerably improved J c (θ) and reduced J c anisotropy in the former over the entire range of the B orientations. However, at higher BZO doping, the BZO nanorods become segmented and misoriented, which may change the Ca diffusion pathways and reduce the benefit of Ca in improving the pinning efficiency of BZO nanorods.

First-principles calculations of the optical response of single-layer and bilayer armchair graphene nanoribbons

Electronic and optical properties of single-layer and bilayer armchair graphene nanoribbons are investigated using a first-principles method. Increased nanoribbon width reduces the band gap and causes a red shift in photon absorption energy. The 3n + 2 family of nanoribbons has the smallest band gaps and lowest onset photon absorption energy among the three families considered due to high π-conjugation indicated by exciton wavefunctions. We also compare the bilayer α and β alignments of armchair graphene nanoribbons with their single-layer counterparts. The extra layer of graphene reduces the band gap and onset photon absorption energy, and the difference between the α alignment and the single-layer configuration is more significant than that of the β alignment and the single layer. Our calculations indicate that the optical properties of graphene nanoribbons depend on the details of atomic structures, including nanoribbon width, edge alignment and number of layers. These characteristics are expected to be important in the design of optoelectronic devices.

Improving HfO2-Based Resistive Switching Devices by Inserting a TaOx Thin Film via Engineered In Situ Oxidation

Resistive switching (RS) devices with binary and analogue operation are expected to play a key role in the hardware implementation of artificial neural networks. However, state of the art RS devices based on binary oxides (e.g., HfO2) still do not exhibit enough competitive performance. In particular, variability and yield still need to be improved to fit industrial requirements. In this study, we fabricate RS devices based on a TaOx/HfO2 bilayer stack, using a novel methodology that consists of the in situ oxidation of a Ta film inside the atomic layer deposition (ALD) chamber in which the HfO2 film is deposited. By means of X-ray reflectivity (XRR) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), we realized that the TaOx film shows a substoichiometric structure, and that the TaOx/HfO2 bilayer stack holds a well-layered structure. An exhaustive electrical characterization of the TaOx/HfO2-based RS devices shows improved switching performance compared to the single-layer HfO2 counterparts. The main advantages are higher forming yield, self-compliant switching, lower switching variability, enhanced reliability, and better synaptic plasticity.

Temperature dependent pinning efficiency in multilayer and single layer BZO/YBCO nanocomposite films

The BaZrO3/YBa2Cu3O7 (BZO/YBCO) interface has been found to affect the vortex pinning efficiency of one-dimensional artificial pinning centers (1D-APC) of BZO. A defective BZO/YBCO interface due to a lattice mismatch of ∼7.7% has been blamed for the reduced pinning efficiency. Recently, we have shown incorporating Ca0.3Y0.7Ba2Cu3O7-x spacer layers in BZO/YBCO nanocomposite film in multilayer (ML) format can lead to a reduced lattice mismatch ∼1.4% through the enlargement of lattice constant of YBCO via Ca diffusion and partial Ca/Cu replacement on Cu-O planes. In this work, the effect of this interface engineering on the BZO 1D-APC pinning efficiency is investigated at temperatures of 65-81 K through a comparison between 2 and 6 vol.% BZO/YBCO ML samples with their single-layer (SL) counterparts. An overall higher pinning force (Fp ) density has been observed on the ML samples as compared to their SL counterparts. Specifically, the peak value of Fp (Fp,max ) for the 6% BZO/YBCO ML film is about ∼ 4 times of that of its SL counterpart at 65 K. In addition, the location of the Fp,max (B max) in the ML samples shifts to higher values as a consequence of enhanced pinning. For the 6% BZO/YBCO ML sample, a much smaller “plateau-like” decrease of the Bmax with increasing temperature was observed, which is in contrast to approximately linear decrease of Bmax with increasing temperature in the 6% SL film. This result indicates the importance of restoring the BZO/YBCO interface quality for better pinning efficiency of BZO 1D-APCs especially at higher BZO doping concentration.

Enhanced water splitting photocatalyst enabled by two-dimensional GaP/GaAs van der Waals heterostructure

Two-dimensional (2D) photocatalysts are promising alternatives to traditional 3D metal oxides. However, it is still a great challenge to surmount the limitation restricted by the 2D photocatalytic bandgap together with the band edge position. Herein, we have newly designed 2D GaP/GaAs van der Waals (vdW) heterostructure-based photocatalyst for water splitting and examined the corresponding operating mechanism. Firstly, the tunable electronic, higher carrier mobilities, and excellent optical properties of XP/XAs (X = Ga, In) vdW heterostructures and single-layer counterparts are introduced based on density functional theory. Specially, the GaP/GaAs vdW heterostructure with direct bandgap exhibits more noticeable optical absorption than the single-layer counterparts. Secondly, intrinsic electric field can be obtained in GaP/GaAs vdW heterostructure and the excited electrons and holes of GaP/GaAs vdW heterostructure are present in opposite layers, demonstrating that the GaP/GaAs vdW heterostructure can spontaneously generate the electron-hole separators. Thirdly, the thermodynamic stability of GaP/GaAs vdW heterostructure has been confirmed, which shows high potential for experimental implementation. Finally, due to the superior characteristics, GaP/GaAs vdW heterostructure has been constructed for the photocatalytic water-splitting. Importantly, the photoexcited electrons of GaP/GaAs vdW heterostructure can spontaneously induce hydrogen half reaction without sacrificial reagents. Moreover, the driving force in oxidation half reaction of GaP/GaAs vdW heterostructure can be greatly boosted under light illumination. Our constructed 2D-vdW-semiconductors-based devices provide a promising strategy to achieve high efficiency water-splitting photocatalyst.

A Bilayer Skin-Inspired Hydrogel with Strong Bonding Interface.

Conductive hydrogels are widely used in sports monitoring, healthcare, energy storage, and other fields, due to their excellent physical and chemical properties. However, synthesizing a hydrogel with synergistically good mechanical and electrical properties is still challenging. Current fabrication strategies are mainly focused on the polymerization of hydrogels with a single component, with less emphasis on combining and matching different conductive hydrogels. Inspired by the gradient modulus structures of the human skin, we propose a bilayer structure of conductive hydrogels, composed of a spray-coated poly(3,4-dihydrothieno-1,4-dioxin): poly(styrene sulfonate) (PEDOT:PSS) as the bonding interface, a relatively low modulus hydrogel on the top, and a relatively high modulus hydrogel on the bottom. The spray-coated PEDOT:PSS constructs an interlocking interface between the top and bottom hydrogels. Compared to the single layer counterparts, both the mechanical and electrical properties were significantly improved. The as-prepared hydrogel showed outstanding stretchability (1763.85 ± 161.66%), quite high toughness (9.27 ± 0.49 MJ/m3), good tensile strength (0.92 ± 0.08 MPa), and decent elastic modulus (69.16 ± 8.02 kPa). A stretchable strain sensor based on the proposed hydrogel shows good conductivity (1.76 S/m), high sensitivity (a maximum gauge factor of 18.14), and a wide response range (0–1869%). Benefitting from the modulus matching between the two layers of the hydrogels, the interfacial interlocking network, and the patch effect of the PEDOT:PSS, the strain sensor exhibits excellent interface robustness with stable performance (>12,500 cycles). These results indicate that the proposed bilayer conductive hydrogel is a promising material for stretchable electronics, soft robots, and next-generation wearables.

Transition-metal hydroxide nanosheets with peculiar double-layer structures as efficient electrocatalysts

Single- or few-layer nanosheets with a molecular-level thickness may provide an ideal model for the fundamental investigation of layer-number-dependent properties. Herein, we report a new strategy for a selective synthesis of transition-metal-containing Co-Fe and Co-Ni-Fe hydroxide nanosheets with peculiar double-layer structures. A unique second-stage phase was obtained from topochemical oxidative intercalation of brucite-type metal hydroxides, e.g., Co5/6Fe1/6(OH)2 and Co2/3Ni1/6Fe1/6(OH)2, with a molar ratio of Fe fixed at 1/6. After anion exchange, the second-stage phase was exfoliated into double-layer hydroxide nanosheets with an average thickness of ∼1.9 nm, which was approximately twice that of their single-layer counterparts (∼1.0 nm). Electrocatalytic measurements combined with theoretic calculations revealed that the double-layer hydroxide nanosheets exhibited excellent oxygen evolution reaction (OER) catalytic activity and kinetics, outperforming their single-layer counterparts, which validates the great potential of transition-metal hydroxide nanosheets with both tunable composition and layer numbers for efficient electrocatalysis.

Joint Beamforming, Power Allocation, and Splitting Control for SWIPT-Enabled IoT Networks with Deep Reinforcement Learning and Game Theory.

Future wireless networks promise immense increases on data rate and energy efficiency while overcoming the difficulties of charging the wireless stations or devices in the Internet of Things (IoT) with the capability of simultaneous wireless information and power transfer (SWIPT). For such networks, jointly optimizing beamforming, power control, and energy harvesting to enhance the communication performance from the base stations (BSs) (or access points (APs)) to the mobile nodes (MNs) served would be a real challenge. In this work, we formulate the joint optimization as a mixed integer nonlinear programming (MINLP) problem, which can be also realized as a complex multiple resource allocation (MRA) optimization problem subject to different allocation constraints. By means of deep reinforcement learning to estimate future rewards of actions based on the reported information from the users served by the networks, we introduce single-layer MRA algorithms based on deep Q-learning (DQN) and deep deterministic policy gradient (DDPG), respectively, as the basis for the downlink wireless transmissions. Moreover, by incorporating the capability of data-driven DQN technique and the strength of noncooperative game theory model, we propose a two-layer iterative approach to resolve the NP-hard MRA problem, which can further improve the communication performance in terms of data rate, energy harvesting, and power consumption. For the two-layer approach, we also introduce a pricing strategy for BSs or APs to determine their power costs on the basis of social utility maximization to control the transmit power. Finally, with the simulated environment based on realistic wireless networks, our numerical results show that the two-layer MRA algorithm proposed can achieve up to 2.3 times higher value than the single-layer counterparts which represent the data-driven deep reinforcement learning-based algorithms extended to resolve the problem, in terms of the utilities designed to reflect the trade-off among the performance metrics considered.

Enabling coherent BaZrO3 nanorods/YBa2Cu3O7−x interface through dynamic lattice enlargement in vertical epitaxy of BaZrO3/YBa2Cu3O7−x nanocomposites

One-dimensional c-axis-aligned BaZrO3 (BZO) nanorods are regarded as strong one-dimensional artificial pinning centers (1D-APCs) in BZO-doped YaBa2Cu3O7−x (BZO/YBCO) nanocomposite films. However, a microstructure analysis has revealed a defective, oxygen-deficient YBCO column around the BZO 1D-APCs due to the large lattice mismatch of ∼7.7% between the BZO (3a = 1.26 nm) and YBCO (c = 1.17 nm), which has been blamed for the reduced pinning efficiency of BZO 1D-APCs. Herein, we report a dynamic lattice enlargement approach on the tensile strained YBCO lattice during the BZO 1D-APCs growth to induce c-axis elongation of the YBCO lattice up to 1.26 nm near the BZO 1D-APC/YBCO interface via Ca/Cu substitution on single Cu-O planes of YBCO, which prevents the interfacial defect formation by reducing the BZO/YBCO lattice mismatch to ∼1.4%. Specifically, this is achieved by inserting thin Ca0.3Y0.7Ba2Cu3O7−x (CaY-123) spacers as the Ca reservoir in 2–6 vol.% BZO/YBCO nanocomposite multilayer (ML) films. A defect-free, coherent BZO 1D-APC/YBCO interface is confirmed in transmission electron microscopy and elemental distribution analyses. Excitingly, up to five-fold enhancement of J c (B) at magnetic field B= 9.0 T//c-axis and 65 K–77 K was obtained in the ML samples as compared to their BZO/YBCO single-layer (SL) counterpart’s. This has led to a record high pinning force density F p together with significantly enhanced B max at which F p reaches its maximum value F p,max for BZO 1D-APCs at B//c-axis. At 65 K, the F p,max ∼158 GN m−3 and B max ∼ 8.0 T for the 6% BZO/YBCO ML samples represent a significant enhancement over F p,max ∼ 36.1 GN m−3 and B max ∼ 5.0 T for the 6% BZO/YBCO SL counterparts. This result not only illustrates the critical importance of a coherent BZO 1D-APC/YBCO interface in the pinning efficiency, but also provides a facile scheme to achieve such an interface to restore the pristine pinning efficiency of the BZO 1D-APCs.

Studies on Colossal Magnetoresistance Behaviour of Pr0.6Sr0.4MnO3/Pr0.5Ca0.5MnO3 Heterostructure Films

Heterostructure bilayer thin films of Pr0.6Sr0.4MnO3/Pr0.5Ca0.5MnO3 were prepared by pulsed laser deposition, and the structural, magnetic and magnetotransport properties were studied, and the results were compared to that of Pr0.6Sr0.4MnO3 and Pr0.5Ca0.5MnO3 single-layer thin films. Structural analysis of the heterostructure reveals c-axis orientation for both the manganite layers. The heterostructure exhibits a higher metal-insulator transition temperature and a larger colossal magnetoresistance near room temperature than that of the single-layer counterparts. The electrical conduction above the metal-insulator transition could be explained within the realm of the adiabatic small polaron hopping mechanism, with lesser activation energies compared to the single-layer films. Magnetization measurements portray the presence of an unsaturated symmetric hysteresis loop for the heterostructure with the Curie temperature of ~270 K corresponding to the ferromagnetic ordering emanating from Pr0.6Sr0.4MnO3. These results could be qualitatively understood considering the combined effect of strain and ferromagnetic proximity of Pr0.6Sr0.4MnO3 with charge-ordered Pr0.5Ca0.5MnO3 manganite.

Design and Development of Banana Leaves-based Double-layer Microwave Absorber

A Double-layer banana leaves-based absorber is designed and can be treated as a potential alternative to conventional MAM. The dielectric relaxation parameters of the dry banana leaves in powder form and the composites of dry banana leaves and charcoal powder have are measured by OCP method using vector network analyzer in the frequency range of 1–16 GHz. Further, the return loss of two single-layers and a double-layer with a thickness of 4 and 8.02 mm, respectively, is investigated in the frequency range of 1–20 GHz. Results show that the electromagnetic properties along with absorption performance of the double layer absorber are appreciably ameliorated as compared to its single-layer counterparts.

Hierarchical Distribution Matching for Probabilistic Amplitude Shaping.

Probabilistic amplitude shaping—implemented through a distribution matcher (DM)—is an effective approach to enhance the performance and the flexibility of bandwidth-efficient coded modulations. Different DM structures have been proposed in the literature. Typically, both their performance and their complexity increase with the block length. In this work, we present a hierarchical DM (Hi-DM) approach based on the combination of several DMs of different possible types, which provides the good performance of long DMs with the low complexity of several short DMs. The DMs are organized in layers. Each upper-layer DM encodes information on a sequence of lower-layer DMs, which are used as “virtual symbols”. First, we describe the Hi-DM structure, its properties, and the encoding and decoding procedures. Then, we present three particular Hi-DM configurations, providing some practical design guidelines, and investigating their performance in terms of rate loss and energy loss. Finally, we compare the system performance obtained with the proposed Hi-DM structures and with their single-layer counterparts: a SNR gain is obtained by a two-layer Hi-DM based on constant composition DMs (CCDM) compared to a single-layer CCDM with same complexity; a gain and a significant complexity reduction are obtained by a Hi-DM based on minimum-energy lookup tables compared to a single-layer DM based on enumerative sphere shaping with same memory requirements.

Symmetry-Resolved Two-Magnon Excitations in a Strong Spin-Orbit-Coupled Bilayer Antiferromagnet.

We used a combination of polarized Raman spectroscopy and spin wave calculations to study magnetic excitations in the strong spin-orbit-coupled bilayer perovskite antiferromagnet Sr_{3}Ir_{2}O_{7}. We observed two broad Raman features at ∼800 and ∼1400 cm^{-1} arising from magnetic excitations. Unconventionally, the ∼800 cm^{-1} feature is fully symmetric (A_{1g}) with respect to the underlying tetragonal (D_{4h}) crystal lattice which, together with its broad line shape, definitively rules out the possibility of a single magnon excitation as its origin. In contrast, the ∼1400 cm^{-1} feature shows up in both the A_{1g} and B_{2g} channels. From spin wave and two-magnon scattering cross-section calculations of a tetragonal bilayer antiferromagnet, we identified the ∼800 cm^{-1} (1400 cm^{-1}) feature as two-magnon excitations with pairs of magnons from the zone-center Γ point (zone-boundary van Hove singularity X point). We further found that this zone-center two-magnon scattering is unique to bilayer perovskite magnets which host an optical branch in addition to the acoustic branch, as compared to their single layer counterparts. This zone-center two-magnon mode is distinct in symmetry from the time-reversal symmetry broken "spin wave gap" and "phase mode" proposed to explain the ∼92 meV (742 cm^{-1}) gap in resonant inelastic x-ray spectroscopy magnetic excitation spectra of Sr_{3}Ir_{2}O_{7}.