High Polarization Research Articles

Two-Dimensional GeS/SnSe2 Tunneling Photodiode with Bidirectional Photoresponse and High Polarization Sensitivity.

A two-dimensional (2D) broken-gap (type-III) p-n heterojunction has a unique charge transport mechanism because of nonoverlapping energy bands. In light of this, type-III band alignment can be used in tunneling field-effect transistors (TFETs) and Esaki diodes with tunable operation and low consumption by highlighting the advantages of tunneling mechanisms. In recent years, 2D tunneling photodiodes have gradually attracted attention for novel optoelectronic performance with a combination of strong light-matter interaction and tunable band alignment. However, an in-depth understanding of the tunneling mechanisms should be further investigated, especially for developing electronic and optoelectronic applications. Here, we report a type-III tunneling photodiode based on a 2D multilayered p-GeS/n+-SnSe2 heterostructure, which is first fabricated by the mechanical exfoliation and dry transfer method. Through the Simmons approximation, its various tunneling transport mechanisms dependent on bias and light are demonstrated as the origin of excellent bidirectional photoresponse performance. Moreover, compared to the traditional p-n photodiode, the device enables bidirectional photoresponse capability, including maximum responsivity values of 43 and 8.7 A/W at Vds = 1 and -1 V, respectively, with distinctive photoactive regions from the scanning photocurrent mapping. Noticeably, benefiting from the in-plane anisotropic structure of GeS, the device exhibits an enhanced photocurrent anisotropic ratio of 9, driven by the broader depletion region at Vds = -3 V under 635 nm irradiation. Above all, the results suggest that our designed architecture can be potentially applied to CMOS imaging sensors and polarization-sensitive photodetectors.

In-Plane Sliding Ferroelectricity Realized in Penta-PdSe2/Penta-PtSe2 van der Waals Heterostructure.

Different from conventional 2D sliding ferroelectrics with polarization switchable in the out-of-plane via interlayer sliding, we show the existence of in-plane sliding ferroelectricity in a bilayer of a pentagon-based van der Waals heterostructure formed by vertically stacking an experimentally synthesized penta-PdSe2 sheet and a crystal lattice well-matched penta-PtSe2 sheet. From the 128 sliding patterns, four stable configurations are found that exhibit in-plane sliding ferroelectricity with an ultralow polarization switching barrier of 1.91 meV/atom and a high ferroelectric polarization of ±17.11 × 10-10 C m-1. Following the ferroelectric transition among the stable sliding configurations, significant changes in carrier mobility, electrical conductivity, and second harmonic generation are identified. In particular, the ferroelectric stacking configurations are found to possess a negative Poisson's ratio, facilitating the experimental characterization of the sliding ferroelectric effect. This study demonstrates that pentagonal sheets can be used to realize 2D in-plane sliding ferroelectrics going beyond the existing ones.

Nanoengineering of Cathode Catalysts for Li-O2 Batteries.

Lithium-oxygen (Li-O2) batteries have obtained widespread attention as next-generation energy storage systems due to their extremely high energy density. However, the high charge overpotential, attributed to the insulating property of Li2O2, significantly limits the energy efficiency and triggers solvent degradation. The high electrochemical activities of oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) on the cathode are crucial for alleviating the high charging polarizations and enhancing the lifetime of Li-O2 batteries, which are also top challenges of state-of-art research. In this review, the scientific challenges and the proposed solutions in the development of cathode catalysts have been summarized. The recent research advancements on the nanoengineering of cathode catalysts for Li-O2 batteries have been comprehensively discussed, and the perspectives on the structure optimization are presented. Meanwhile, we have elucidated the structure-performance relationship between the electronic state and performance of the cathode catalysts at the nanoscale level. This review intends to provide guidelines for the design and construction of cathode catalysts in advanced Li-O2 batteries.

High polarization stability induced by light-activated defect engineering in ferroelectric single crystals

Ferroelectric crystals possess good physical properties, which endow them with great potential in photovoltaic, piezoelectric, and electro-optic applications. The polarization stability of ferroelectric crystals is crucial for device applications, because their performance mostly relies on the engineering of domain structures. In this paper, we show that the polarization stability can be improved through light illumination during poling; the obtained Mn and Fe-doped KTa1-xNbxO3 (Mn&Fe: KTN) single crystals maintained stable single-domain state and excellent electro-optic properties over a 1-year observation period. We propose a possible mechanism for the improved polarization stability through light-activated defect engineering, and also investigate the effect of light illumination on defect states in KTN crystals. Appropriate ions doping and light activation effect are shown to be the effective method for achieving high polarization stability after electric field poling. The light-activated defect engineering promotes the stabilization of polarization structures, which is beneficial for the development of high-performance applications based on ferroelectric crystals.

Evaporation Dynamics on a Lithium Niobate Surface.

Manipulating the water evaporation dynamics is a prerequisite in various modern-day applications like DNA stretching, rapid disease diagnostics, and inkjet printing. One method to affect the evaporation dynamics of droplets is to externally apply electric fields. However, surfaces that bear an intrinsic surface charge have not yet been investigated with respect to their evaporation behavior. In this study, we investigate water droplet evaporation on lithium niobate (LN), a ferroelectric material with a very high spontaneous polarization of 0.7 . Our results show that a droplet deposited on an LN surface evaporates in three stages: (i) constant contact radius (ii) mixed phase (iii) stick-slip, which is likely originating from the intrinsic surface charge. The influence of the polarization direction of the LN surface as well as the relative humidity of the environment on various evaporation characteristics were studied. The results suggest that the specific adsorption layers forming on charged surfaces, e. g. from the humidity of the surrounding air, play a key role in the evaporation process. Furthermore, compared to other materials with similar contact angles, LN demonstrated a significantly large evaporation rate. This property might also be attributed to the intrinsic surface charge and could be exploited in heat transfer applications.

The Development and Performance of a Gemini Viscoelastic Surfactant with Tricationic Groups Applied in Unconventional Oil and Gas Reservoir Stimulation

AbstractTo improve water solubility and salt tolerance of viscoelstic surfactants (VESs), modifying the spacer of Gemini VES was adopted and a novel Gemini VES nominated TC‐2OH, with tri‐cationic groups and double hydroxyls on the spacer, was developed. The basic surface activity properties of TC‐2OH and the molecular aggregate behavior stimulated by NaCl or NaSal were measured and analyzed to investigate the mechanism of viscoelastic fluid forming by TC‐2OH solution, and it proved that TC‐2OH is more sensitive to NaSal, compared with NaCl, due to the embedded structure of salicylate. The molecular structure of TC‐2OH imparts excellent solubility to itself, and with the assistance of ethanol, the dissolution time in water can be shortened to within 45 seconds. In addition, oscillation experiments, heat and shear resistant experiments, and drag reduction tests were conducted to study the advantage of NaSal for stimulating the formation of the slickwater compared with NaCl. The slickwater stimulated by NaSal indeed exhibit superior drag reduction and proppant carrying capacity. To effectively disassemble the wormlike micelles for gel breaking, ethylene glycol butyl ether performs better than the hydrocarbons because of its high polarity and water solubility. The gel breaking fluids of slickwater caused extremely low damage to the tight sandstone cores. The successful development of TC‐2OH enables instant preparation of slickwater and variable‐viscosity for fracturing in unconventional reservoirs, which also realizes convenient switching between the slickwater with different viscosity.

A lightweight and efficient hollow sunken carbon@MnO2/reduced graphene oxide composite for high-performance electromagnetic wave absorption

To address the environmental and health issues stemming from electromagnetic pollution, it is crucial to investigate high-performance and practical materials for absorbing electromagnetic waves. Herein, the ternary lightweight SC@MnO2/RGO (SCMR) composites are synthesized by using a special kind of hollow sunken carbon nanoparticles (SC) as a substrate and combining MnO2 nanosheets with 2D reduced graphene oxide (RGO). The investigation results show that the minimum reflection loss (RLmin) of SCMR3 can reach −60.95 dB with a matched thickness of 1.47 mm and a frequency of 13.12 GHz, and the effective absorption bandwidth (EAB) is 4.08 GHz (13.76–17.84 GHz) at the thickness of 1.23 mm. Its excellent performance comes from high dielectric loss capability, multiple reflections, interfacial polarization, and defective polarization relaxation brought by the structure of the composite, which can effectively enable electromagnetic wave absorption and facilitates energy conversion. Furthermore, simulation-based assessment under far-field conditions elucidates the radar stealth effect, demonstrating that the maximum radar cross-section (RCS) attenuation value of SCMR3-coated perfect electrical conductor (PEC) at Phi = 0° and θ = 0° can attain 32.13 dB m2. Ultimately, this study presents a viable design methodology for developing lightweight, efficient, and application-oriented carbon-based electromagnetic wave absorption materials.

Light-Boosting Highly Sensitive and Ultrafast Piezoelectric Sensor Based on Composite Membrane of Copper Phthalocyanine and Graphene Oxide.

Self-powered wearable pressure sensors based on flexible electronics have emerged as a new trend due to the increasing demand for intelligent and portable devices. Improvements in pressure-sensing performance, including in the output voltage, sensitivity and response time, can greatly expand their related applications; however, this remains challenging. Here, we report on a highly sensitive piezoelectric sensor with novel light-boosting pressure-sensing performance, based on a composite membrane of copper phthalocyanine (CuPC) and graphene oxide (GO) (CuPC@GO). Under light illumination, the CuPC@GO piezoelectric sensor demonstrates a remarkable increase in output voltage (381.17 mV, 50 kPa) and sensitivity (116.80 mV/kPa, <5 kPa), which are approximately twice and three times of that the sensor without light illumination, respectively. Furthermore, light exposure significantly improves the response speed of the sensor with a response time of 38.04 µs and recovery time of 58.48 µs, while maintaining excellent mechanical stability even after 2000 cycles. Density functional theory calculations reveal that increased electron transfer from graphene to CuPC can occur when the CuPC is in the excited state, which indicates that the light illumination promotes the electron excitation of CuPC, and thus brings about the high polarization of the sensor. Importantly, these sensors exhibit universal spatial non-contact adjustability, highlighting their versatility and applicability in various settings.

Highly-Polarized Emission Provided by Giant Optical Orientation of Exciton Spins in Lead Halide Perovskite Crystals.

Quantum technologic and spintronic applications require reliable material platforms that enable significant and long-living spin polarization of excitations, the ability to manipulate it optically in external fields, and the possibility to implement quantum correlations between spins, i.e., entanglement. Here it is demonstrated that these conditions are met in bulk crystals of lead halide perovskites. A giant optical orientation of 85% of excitons, approaching the ultimate limit of unity, in FA0.9Cs0.1PbI2.8Br0.2 crystals is reported. The exciton spin orientation is maintained during the exciton lifetime of 55ps resulting in high circular polarization of the exciton emission. The optical orientation is robust to detuning of the excitation energy up to 0.3eV above the exciton resonance and remains larger than 20% up to detunings of 0.9eV. It evidences pure chiral selection rules and suppressed spin relaxation of electrons and holes, even with large kinetic energies. The exciton and electron-hole recombinations are distinguished by means of the spin dynamics detected via coherent spin quantum beats in magnetic field. Further, electron-hole spin correlations are demonstrated through linear polarization beats after circularly polarized excitation. These findings are supported by atomistic calculations. All-in-all, the results establish lead halide perovskite semiconductors as suitable platform for quantumtechnologies.

Enhanced surface performance of insulating ceramic by plasma polymerization with nanosecond-pulse dielectric barrier discharge: Insight into the effect of the repetition frequency

Insulating ceramics are widely used in power systems, but their high polarity makes them prone to wet and pollution flashover. In this paper, an Ar/polydimethylsiloxane dielectric barrier discharge excited by a parametric nanosecond-pulse power source is utilized for plasma polymerization to enhance ceramic surface insulating performance. Diagnosis of the discharge characteristics and surface physiochemical properties is conducted at different repetition frequencies to investigate the mechanism associated with the relationship between repetition frequency and the plasma polymerization process. The results indicate that a superhydrophobic surface can be achieved at repetition frequencies above 2 kHz. This transformation brings about multiple effects, including a decrease in surface polarity, an increase in charge dissipation, and an improvement in surface dry and wet flashover voltages. It is discovered that the discharge mode shifts from homogeneous to filamentary due to the memory effect of high repetition frequencies. Additionally, several filaments are generated simultaneously during a single pulse, facilitating the polymerization reactions. For high repetition frequencies, a low-polarity silicon-containing film with micro-nanometer structures is deposited on the ceramic surface, while scattered polymer fragments are generated on the surface without a cross-linked film for repetition frequencies below 2 kHz, despite longer treatment durations.

High-performance lithium-ion full-cell batteries based on transition metal oxides: Towards energy density of ∼ 1300 Wh kg−1

Half-cell structure including sufficient lithium ions for theoretical studies exhibits different electrochemical performance with commercial full-cell rechargeable lithium ion batteries (LIBs) featuring moderate lithium ions. So, understanding the property correlation between half-cell and full-cell LIBs is imperative, but remains a big challenge. Herein, a series of full-cells are assembled with transition metal oxide (TMO) nanowires as cathodes and silicon/graphite (Si/G) anode via electrochemical pre-lithiation, to figure out the key determinants in comparison to their corresponding half-cells. It is found that eletrochemical performances of half-cell and full-cell batteries are basically consistent by using insertion-type cathodes of V2O5, MoO3 and MnO2, but different in the cases of conversion-type cathodes of Fe2O3 and Co3O4 due to their high polarization relieved crystal fragmentation. In addition, compared with the other five materials, V2O5 nanowire exhibits the lowest charge transfer resistance (240.2 Ω), highest lithium ion diffusion rate (10-13 ∼ 10-11 cm2 s−1) and discharge midpoint voltage (1.6 V). Thus, V2O5||PL-Si/G achieves the state-of-the-art gravimetric energy density, discharge midpoint voltage and cycle performance, giving rise to the record-high 1288 Wh kg−1 at 0.1 A g-1 in potential range of 0.3 ∼ 4.0 V. These results indicate the significance of rational material selection and effective pre-lithiation for developing high-performance full-cell LIBs.

Scalable Nanoimprint Manufacturing of Functional Multilayer Metasurface Devices

AbstractOptical metasurfaces, consisting of subwavelength‐scale meta‐atom arrays, hold great promise of overcoming the fundamental limitations of conventional optics. Due to their structural complexity, metasurfaces usually require high‐resolution yet slow and expensive fabrication processes. Here, using a metasurface polarimetric imaging device as an example, the photonic structures and the Nanoimprint lithography (NIL) processes are designed, creating two separate NIL molds over a patterning area of &gt; 20 mm2 with designed Moiré alignment markers by electron‐beam writing, and further subsequently integrate silicon and aluminum metasurface structures on a chip. Uniquely, the silicon and aluminum metasurfaces are fabricated by using the nanolithography and 3D pattern‐transfer capabilities of NIL, respectively, achieving nanometer‐scale linewidth uniformity, sub‐200 nm translational overlay accuracy, and &lt;0.017 rotational alignment error while significantly reducing fabrication complexity and surface roughness. The micro‐sized multilayer metasurfaces have high circular polarization extinction ratios as large as ≈20 and ≈80 in blue and red wavelengths. Further, the metasurface chip‐integrated CMOS imager demonstrates high accuracy in broad‐band, full Stokes parameter analysis in the visible wavelength ranges and single‐shot polarimetric imaging. This novel, NIL‐based, multilayered nanomanufacturing approach is applicable to the scalable production of large‐area functional structures for ultra‐compact optic, electronic, and quantum devices.

Promising interlayer sensitization strategy for the construction of high-performance blue hyperfluorescence OLEDs

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials are promising candidates for organic light-emitting diodes (OLEDs) with narrow electroluminescence (EL) spectra. Current researches focus on fabricating hyperfluorescence OLEDs to improve EL efficiencies of MR-TADF emitters by co-doping them with TADF sensitizers in a single host layer. However, in many cases, the polarity of the single host could be not suitable for both blue MR-TADF emitters and blue TADF sensitizers, resulting in broadened EL spectra in high-polar hosts or decreased EL efficiencies in low-polar hosts. Herein, we wish to report an efficient sensitization strategy for blue MR-TADF emitters by constructing an interlayer-sensitizing configuration, in which the blue TADF sensitizers and blue MR-TADF emitters are separated into two closely aligned host layers with high polarity and low polarity, respectively. Based on this strategy, efficient blue hyperfluorescence OLEDs are realized and verified by employing various TADF sensitizers and different MR-TADF emitters, furnishing outstanding external quantum efficiencies of up to 38.8% and narrow EL spectra. These results validate the feasibility and universality of this interlayer sensitization strategy, which provides an effective alternative to high-performance blue hyperfluorescence OLEDs.

Enhancing atomic ordering, magnetic and transport properties of Mn2VGa Heusler alloy thin films toward negatively spin-polarized charge injection

Magnetic materials with negative spin polarization have attracted attention for their potential to increase the design freedom of spintronic devices. This study investigated the effects of off-stoichiometry on the atomic ordering, microstructure, and magneto-transport properties in Mn2+xV1−xGa (x = −0.2, 0, +0.2, +0.4) Heusler alloy films, which are predicted to have large negative spin polarization derived from a pseudo band gap in the majority spin channel. The Mn2+xV1−xGa films epitaxially grown on MgO(001) substrates exhibits variations of B2 and L21 order with the Mn concentration. A high-quality L21 ordered film was achieved in the Mn-rich composition (x = +0.2) with B2 and L21 order parameters of 0.97 and 0.86, respectively, and a saturation magnetization of 1.4 μB/f.u., which agrees with the Slater-Pauling rule. Scanning transmission electron microscopy observations showed that B2 and L21 phases coexist in Mn-poor and stoichiometric films, while the L21 phase is dominant in the Mn-rich film with small amounts of Mn–V and Mn–Ga disorders, as revealed by laboratory and anomalous X-ray diffraction. Combined first-principles calculations and anisotropic magnetoresistance analysis confirms that the addition of excess Mn preserves the high spin polarization by suppressing the formation of detrimental antisites of V atoms occupying Mn sites. Therefore, the Mn-rich composition is promising for negatively spin-polarized charge injection in Mn2VGa-based spintronic applications.

Polymorphic Heterogeneous Polar Structure Enabled Superior Capacitive Energy Storage in Lead-Free Relaxor Ferroelectrics at Low Electric Field.

High-performance energy storage dielectrics capable of low/moderate field operation are vital in advanced electrical and electronic systems. However, in contrast to achievements in enhancing recoverable energy density (Wrec), the active realization of superior Wrec and energy efficiency (η) with giant energy-storage coefficient (Wrec/E) in low/moderate electric field (E) regions is much more challenging for dielectric materials. Herein, lead-free relaxor ferroelectrics are reported with giant Wrec/E designed with polymorphic heterogeneous polar structure. Following the guidance of Landau phenomenological theory and rational composition construction, the conceived (Bi0.5Na0.5)TiO3-based ternary solid solution that delivers giant Wrec/E of ≈0.0168 µCcm-2, high Wrec of ≈4.71 J cm-3 and high η of ≈93% under low E of 280kVcm-1, accompanied by great stabilities against temperature/frequency/cycling number and excellent charging-discharging properties, which is ahead of most currently reported lead-free energy storage bulk ceramics measured at same E range. Atomistic observations reveal that the correlated coexisting local rhombohedral-tetragonal polar nanoregions embedded in the cubic matrix are constructed, which enables high polarization, minimized hysteresis, and significantly delayed polarization saturation concurrently, endowing giant Wrec/E along with high Wrec and η. These findings advance the superiority and feasibility of polymorphic nanodomains in designing highly efficient capacitors for low/moderate field-region practical applications.

Cu(N2)-Li Battery for Ammonia Synthesis.

The cathodic mechanism of Li-N2 batteries is similar to Li-mediated N2 reduction (LiNR). Herein, the Li-N2, LiNR, and Cu-Li battery were amalgamated to a milliliter-scale Cu(N2)-Li system. The utilization of a lithium anode with lithium oxidation reaction (LiOR), ensures an uninterrupted supply of lithium ions to active N2. LiOR not only enhances electrolyte stability but also reduces voltage by stripping Li ions, in contrast to the inert platinum anode, commonly employed in LiNR. Notably, an unusual observation of ammonia accumulation within the anode chamber elucidates the presence and role of reaction intermediates. The charging process aimed at lithium regeneration faces high polarization, and a cycling procedure involving low-current charging was proposed to improve cycling. This study integrates insights from three distinct research directions to leverage their respective advantages and scientific insights. The Li-N2 battery emerges as a highly advantageous strategy for ammonia synthesis due to the progressiveness of lithium anode.

Orbital variability of polarized X-ray radiation reflected from a companion star in X-ray binaries

The reflection of X-ray radiation produced near a compact object from its stellar companion contributes to the orbital variability of polarization in X-ray binaries. The X-rays are reflected mainly via Thomson scattering resulting in a high polarization. The orbital variability of the polarization strongly depends on the inclination and the orbital parameters allowing us to constrain them. To explore this phenomenon, we present analytical single-scattering models for the polarized reflection. We find that while diluted by the direct emission, the reflection can produce a polarization degree of about 1&lt;!PCT!&gt; in the case of a large reflection albedo. We fitted the orbital variations of the X-ray polarization observed by the Imaging X-ray Polarimetry Explorer from an accreting weakly magnetized neutron star "clocked burster" GS 1826$-$238 and found that the amplitude of the variations is too large to be primarily caused by the companion star. The polarized reflection is more significant if the compact object is obscured from the observer, and thus it should be more easily observable in certain high-inclination targets.

Evaluation of the electrochemical interaction in the asphalt emulsion-aggregate system of cold mix asphalt through zeta potential and surface free energy analysis

ABSTRACT The interaction in the emulsion-aggregate system is well known and influences the Cold Mix Asphalt (CMA) performance. However, the electrochemical interaction indexes for the emulsion-aggregate systems are still not well understood. Therefore, the present investigation focussed on evaluating the electrochemical interaction in the Asphalt Emulsion-Aggregate system (AEA-S) of Cold Mix Asphalt (CMA). Zeta Potential (ZP), X-ray diffraction (XRD), and Surface Free Energy (SFE) analysis were carried out in three slow-setting cationic asphalt emulsions and three common Colombian aggregates (alluvial and quarried) to determine the electrical potential and interaction in the emulsion-aggregate system. Zeta Potential analysis shows both dependence on the chemical compounds of the aggregates and variation in pH conditions. Moreover, Zeta Potential shows negative values for all three aggregates in the entire pH range variation and decreases with asphalt emulsions pH associated with SiO 2 / Al 2 O 3 ratio. Through chemical identification and electrokinetic forces is feasible to conclude that high Zeta Potential (ZP) and Surface Free Energy (SFE) values improve the electrochemical ad of the asphalt emulsion-aggregate system (AEA-S), demonstrating that high polarity is an essential factor in Cold Mix Asphalts (CMA).

Theoretical analysis of magnetic, optoelectronic, and thermoelectric properties of Cs2CuCrX6 (X = Cl and Br) double perovskites for spintronic and data storage devices

Spintronics is an emerging field that has the potential to replace conventional electronics due to their comparatively high speed, low power consumption, and infinite endurance. The phenomena of ferromagnetism with high spin polarization in double perovskites make them the desired materials for spintronics. In the present work, the structure of Cs2CuCrX6 (X = Cl and Br) and their magnetic and optoelectronic properties were studied by utilizing density functional theory (DFT). For the calculations of exchange-correlation potential, PBE-sol approximation was utilized while for the accurate measurement of electronic band structure and density of states (DOS), we employed mBJ potential. Both materials exhibit cubic structure and are thermodynamically stable as confirmed by volume optimization and negative formation energy respectively. Spin-based energy-volume optimization and values of exchange constants reveal the ferromagnetic nature of materials. It has been observed that 3-d states of Cr are responsible for ferromagnetism and have the major contribution to the net magnetic moment caused by exchange splitting. Furthermore, investigations of band structure and electronic density of states showed that both Cs2CuCrCl6 and Cs2CuCrBr6 were indirect bandgap (Eg) semiconductors with the Eg values of 1.2 eV and 0.33 eV respectively. The optical spectra of materials showed strong absorption in the ultraviolet region. Lastly, the transport and thermoelectric properties (TE) of materials were investigated in the range of temperature 300 K–800 K by using the BoltzTrap code. The transport parameter which included the electrical conductivity (σ/τ) and thermal conductivity (κe/τ) of the materials showed a decreasing trend with temperature whereas the Seebeck coefficient (S) and Power factor (P.F) showed an increasing trend for Cs2CuCrCl6 while decreases in case of Cs2CuCrBr6. Furthermore, a high figure of merit (ZT) with values of 0.75 and 0.64 was obtained for Cs2CuCrCl6 and Cs2CuCrBr6 respectively. The results of this work are encouraging and show the capabilities of the discussed materials in the fields of spintronics, thermoelectric, and optoelectronics.

Dense Polarized Positrons from Beam-Solid Interaction.

Relativistic positron sources with high spin polarization have important applications in nuclear and particle physics and many frontier fields. However, it is challenging to produce dense polarized positrons. Here we present a simple and effective method to achieve such a positron source by directly impinging a relativistic high-density electron beam on the surface of a solid target. During the interaction, a strong return current of plasma electrons is induced and subsequently asymmetric quasistatic magnetic fields as high as megatesla are generated along the target surface. This gives rise to strong radiative spin flips and multiphoton processes, thus leading to efficient generation of copious polarized positrons. With three-dimensional particle-in-cell simulations, we demonstrate the production of a dense highly polarized multi-GeV positron beam with an average spin polarization above 40% and nC-scale charge per shot. This offers a novel route for the studies of laserless strong-field quantum electrodynamics physics and for the development of high-energy polarized positron sources.