Highly Efficient Spin-Orbit Torque Switching in Bi2Se3/Fe3GeTe2 van der Waals Heterostructures.

Topological insulators (TIs) have shown promise as a spin-generating layer to switch the magnetization state of ferromagnets via spin-orbit torque (SOT) due to charge-to-spin conversion efficiency of the TI surface states that arises from spin-momentum locking. However, when TIs are interfaced with conventional bulk ferromagnetic metals, the combination of charge transfer and hybridization can potentially destroy the spin texture and hamper the possibility of accessing the TI surface states. Here, we fabricate an all van der Waals (vdW) heterostructure consisting of molecular beam epitaxy grown bulk-insulating Bi2Se3 and exfoliated 2D metallic ferromagnet Fe3GeTe2 (FGT) with perpendicular anisotropy. By detecting the magnetization state of the FGT via anomalous Hall effect and magneto-optical Kerr effect measurements, we determine the critical switching current density for magnetization switching to be Jc ≈ 1.2 × 106 A/cm2, the lowest reported for the switching of a perpendicular anisotropy ferromagnet using Bi2Se3. From second harmonic Hall measurements, we further determine the SOT efficiency (ξDL) to be in the range of 1.8 ± 0.3 and 1.4 ± 0.08 between 5 and 150 K, comparable to the highest values reported for Bi2Se3. Our density functional theory calculations find that the weak interlayer interactions at the Bi2Se3/FGT interface lead to a weakened dipole at the interface and suppress the proximity induced magnetic moment on Bi2Se3. This enables direct access to the TI surface states contributed by the first quintuple layer, where the spins are singly degenerate with significant net in-plane spin polarization. Our results highlight the clear advantage of all-vdW heterostructures with weak interlayer interactions that can enhance SOT efficiency and minimize critical current density, an important step toward realizing next generation low-power nonvolatile memory and spintronic devices.

Mapping the intrinsic photocurrent streamlines through micromagnetic heterostructure devices.

Photocurrent in quantum materials is often collected at global contacts far away from the initial photoexcitation. This collection process is highly nonlocal. It involves an intricate spatial pattern of photocurrent flow (streamlines) away from its primary photoexcitation that depends sensitively on the configuration of current collecting contacts as well as the spatial nonuniformity and tensor structure of conductivity. Direct imaging to track photocurrent streamlines is challenging. Here, we demonstrate a microscopy method to image photocurrent streamlines through ultrathin heterostructure devices comprising platinum on yttrium iron garnet (YIG). We accomplish this by combining scanning photovoltage microscopy with a uniform rotating magnetic field. Here, local photocurrent is generated through a photo-Nernst type effect with its direction controlled by the external magnetic field. This enables the mapping of photocurrent streamlines in a variety of geometries that include conventional Hall bar-type devices, but also unconventional wing-shaped devices called electrofoils. In these, we find that photocurrent streamlines display contortion, compression, and expansion behavior depending on the shape and angle of attack of the electrofoil devices, much in the same way as tracers in a wind tunnel map the flow of air around an aerodynamic airfoil. This affords a powerful tool to visualize and characterize charge flow in optoelectronic devices.

Effects of as-if risk framing of hazards on risk perception and its rebuttal.

BACKGROUND: The difference between hazard and risk is crucial in risk assessment but rather unknown by non-experts. Hyper-partisan activists could use this knowledge gap to amplify risk perception by framing hazards as as-if risks, i.e., describing hazards as if their exposure is critical. Thus, using this as-if risk framing can trigger impressions that a risk is present. Until now, this framing technique and its rebuttal was not empirically analyzed. METHOD: An experimental 2 × 2 factorial online study (N = 404) with repeated measures after intervention was conducted to investigate how framing (hazard vs. as-if risk) and stigmatization (stigmatized vs. non-stigmatized chemical agent) affects affective and cognitive risk perception using an example of exposure to drifting pesticides. RESULTS: As-if risk framing increased risk perception, effects of stigmatization were not observed. However, the a-priori risk perception influences the recorded risk perceptions after the experimental treatment. Rebuttal was successful, i.e., subjects with elevated risk perceptions due to as-if risk framing reduced their risk perception after receiving corrective information. CONCLUSIONS: As-if risk framing investigated here is not a sequestered case. Accordingly, the present study may offer general insights into correcting biased information that neglects the difference between hazard and risk. Risk communicators can benefit from these insights.

Emergent Moiré Phonons Due to Zone Folding in WSe2-WS2 Van der Waals Heterostructures.

Bilayers of 2D materials offer opportunities for creating devices with tunable electronic, optical, and mechanical properties. In van der Waals heterostructures (vdWHs) where the constituent monolayers have different lattice constants, a moiré superlattice forms with a length scale larger than the lattice constant of either constituent material regardless of twist angle. Here, we report the appearance of moiré Raman modes from nearly aligned WSe2-WS2 vdWHs in the range of 240-260 cm-1, which are absent in both monolayers and homobilayers of WSe2 and WS2 and in largely misaligned WSe2-WS2 vdWHs. Using first-principles calculations and geometric arguments, we show that these moiré Raman modes are a consequence of the large moiré length scale, which results in zone-folded phonon modes that are Raman active. These modes are sensitive to changes in twist angle, but notably, they occur at identical frequencies for a given small twist angle away from either the 0-degree or 60-degree aligned heterostructure. Our measurements also show a strong Raman intensity modulation in the frequency range of interest, with near 0 and near 60-degree vdWHs exhibiting a markedly different dependence on excitation energy. In near 0-degree aligned WSe2-WS2 vdWHs, a nearly complete suppression of both the moiré Raman modes and the WSe2 A1g Raman mode (∼250 cm-1) is observed when exciting with a 532 nm CW laser at room temperature. Temperature-dependent reflectance contrast measurements demonstrate the significant Raman intensity modulation arises from resonant Raman effects.

Proximity-magnetized quantum spin Hall insulator: monolayer 1 T' WTe2/Cr2Ge2Te6.

Van der Waals heterostructures offer great versatility to tailor unique interactions at the atomically flat interfaces between dissimilar layered materials and induce novel physical phenomena. By bringing monolayer 1 T' WTe2, a two-dimensional quantum spin Hall insulator, and few-layer Cr2Ge2Te6, an insulating ferromagnet, into close proximity in an heterostructure, we introduce a ferromagnetic order in the former via the interfacial exchange interaction. The ferromagnetism in WTe2 manifests in the anomalous Nernst effect, anomalous Hall effect as well as anisotropic magnetoresistance effect. Using local electrodes, we identify separate transport contributions from the metallic edge and insulating bulk. When driven by an AC current, the second harmonic voltage responses closely resemble the anomalous Nernst responses to AC temperature gradient generated by nonlocal heater, which appear as nonreciprocal signals with respect to the induced magnetization orientation. Our results from different electrodes reveal spin-polarized edge states in the magnetized quantum spin Hall insulator.

Personal Protective Measures during the COVID-19 Pandemic in Germany.

OBJECTIVES: The coronavirus SARS-CoV-2 is highly contagious and can only be contained if the majority of the population takes measures to protect themselves against infection. The present study aimed to investigate personal protective measures, their development over the course of the pandemic in Germany, and potential differences in behavior in terms of sex, age, and education. METHODS: Data from 20 waves of the serial cross-sectional study "BfR-Corona-Monitor" were analyzed. The total sample consisted of N = 20,317 respondents (about 1000 per wave). Data were collected through telephone surveys between June 2020 and March 2021. RESULTS: To protect themselves from infection, participants primarily relied on wearing covers for mouth and nose, keeping their distance from other individuals, and washing their hands thoroughly. Analyses over time showed a strong positive correlation between the number of measures taken and the national incidence rate. Sociodemographic differences also emerged, with women and those who are higher educated as well as younger respondents taking a higher number of protective measures. CONCLUSIONS: Our results indicated that in times of greater infection risks, individuals adapted accordingly and took more protective measures. However, on the basis of sociodemographic differences, campaigns should especially focus on older individuals, the male sex, and those with lower education to enhance their protective behavior.

Serial cross-sectional data on the public's perception on the coronavirus during the first months of the pandemic in Germany.

The coronavirus pandemic poses major challenges for governments and public health authorities. In order to implement appropriate measures, it is important to understand how the population is coping with the pandemic. This dataset contains serial cross-sectional survey data from the first months of the coronavirus pandemic in Germany. Data were collected between 24 March and 26 May 2020 in ten weekly surveys (ns ranging between 500 and 515, in total N = 5,076) as part of omnibus telephone interviews. Samples were drawn at random from landline and mobile telephone numbers. The main topics of the questionnaire were (a) the expected impact of the coronavirus on one's personal life, (b) perception of infection risk, (c) protective measures and (d) information behaviour. Data were weighted to ensure sociodemographic representativeness. To account for the rapidly changing situation of the coronavirus pandemic in Germany, the questionnaire underwent several adjustments during the data collection period.

Kitchen Hygiene in the Spotlight: How Cooking Shows Influence Viewers' Hygiene Practices.

Poor hygiene when handling food is a major cause of foodborne illness. To investigate whether hygiene practices visible in television cooking shows influence viewers' kitchen hygiene, a study on the adoption of demonstrated hygiene behavior was conducted under controlled, experimental conditions. In a study ostensibly on cooking by following recipes participants (n = 65) were randomly assigned to one of three conditions, in which they watched a cooking video that differed only with regard to the hygiene behavior of the chef. In condition 1, the chef engaged in poor hygiene practices while preparing the dish, in condition 2 the chef's hygiene behavior was exemplary and in condition 3, the chef's hygiene behavior was not visible (control condition). After watching the video, participants were instructed to cook the recipe individually in the fully equipped laboratory kitchen. Cooking sessions were videotaped and experimenters blind to condition coded hygiene lapses committed by participants. The level of kitchen hygiene displayed in the cooking video significantly affected hygiene practices of participants cooking the recipe. Participants who had watched the cooking video with correct hygiene practices committed significantly fewer hygiene lapses than those who had watched the video with poor hygiene practices. From a risk communication perspective, TV cooking shows are well placed to convey knowledge of essential hygiene practices during food preparation to a broad audience. To facilitate behavioral change toward safer food-handling practices among viewers, visibly performing correct hygiene practices in cooking shows is a promising strategy.

Communicating Food Risk-Benefit Assessments: Edible Insects as Red Meat Replacers.

Risk-benefit Assessment (RBA) is an emerging methodology in the area of Food and Nutrition that offers a simultaneous evaluation of both risks and benefits linked to dietary choices. Communication of such research to consumers may present a challenge due to the dual nature of RBA. We present a case study of a communication strategy developed for the NovRBA-project. The NovRBA-project (Novel foods as red meat replacers-an insight using Risk Benefit Assessment methods) performed a risk-benefit assessment to evaluate the overall health impact of substituting red meat (beef) by a novel food (house cricket), considering the microbial, toxicological and nutritional characteristics of the respective dietary choices. A literature review of risk perceptions and acceptance of beef and insects as food formed the basis of the communication strategy for the study's results, drawing on environmental and emotional as well as health-related motivations to consume or avoid either food and considering the sociodemographic characteristics of likely consumers. Challenges and future directions for consumer protection organizations communicating findings of risk-benefit analyses on food safety are discussed.

Unveiling Valley Lifetimes of Free Charge Carriers in Monolayer WSe2.

We report on nanosecond-long, gate-dependent valley lifetimes of free charge carriers in monolayer WSe2, unambiguously identified by the combination of time-resolved Kerr rotation and electrical transport measurements. While the valley polarization increases when tuning the Fermi level into the conduction or valence band, there is a strong decrease of the respective valley lifetime consistent with both electron-phonon and spin-orbit scattering. The longest lifetimes are seen for spin-polarized bound excitons in the band gap region. We explain our findings via two distinct, Fermi-level-dependent scattering channels of optically excited, valley-polarized bright trions either via dark or bound states. By electrostatic gating we demonstrate that the transition-metal dichalcogenide WSe2 can be tuned to be either an ideal host for long-lived localized spin states or allow for nanosecond valley lifetimes of free charge carriers (>10 ns).

Spin current from sub-terahertz-generated antiferromagnetic magnons.

Spin dynamics in antiferromagnets has much shorter timescales than in ferromagnets, offering attractive properties for potential applications in ultrafast devices1-3. However, spin-current generation via antiferromagnetic resonance and simultaneous electrical detection by the inverse spin Hall effect in heavy metals have not yet been explicitly demonstrated4-6. Here we report sub-terahertz spin pumping in heterostructures of a uniaxial antiferromagnetic Cr2O3 crystal and a heavy metal (Pt or Ta in its ß phase). At 0.240 terahertz, the antiferromagnetic resonance in Cr2O3 occurs at about 2.7 tesla, which excites only right-handed magnons. In the spin-canting state, another resonance occurs at 10.5 tesla from the precession of induced magnetic moments. Both resonances generate pure spin currents in the heterostructures, which are detected by the heavy metal as peaks or dips in the open-circuit voltage. The pure-spin-current nature of the electrically detected signals is unambiguously confirmed by the reversal of the voltage polarity observed under two conditions: when switching the detector metal from Pt to Ta, reversing the sign of the spin Hall angle7-9, and when flipping the magnetic-field direction, reversing the magnon chirality4,5. The temperature dependence of the electrical signals at both resonances suggests that the spin current contains both coherent and incoherent magnon contributions, which is further confirmed by measurements of the spin Seebeck effect and is well described by a phenomenological theory. These findings reveal the unique characteristics of magnon excitations in antiferromagnets and their distinctive roles in spin-charge conversion in the high-frequency regime.

Coexistence of Magnetic Orders in Two-Dimensional Magnet CrI3.

The magnetic properties in two-dimensional van der Waals materials depend sensitively on structure. CrI3, as an example, has been recently demonstrated to exhibit distinct magnetic properties depending on the layer thickness and stacking order. Bulk CrI3 is ferromagnetic (FM) with a Curie temperature of 61 K and a rhombohedral layer stacking, whereas few-layer CrI3 has a layered antiferromagnetic (AFM) phase with a lower ordering temperature of 45 K and a monoclinic stacking. In this work, we use cryogenic magnetic force microscopy to investigate CrI3 flakes in the intermediate thickness range (25-200 nm) and find that the two types of magnetic orders, hence the stacking orders, can coexist in the same flake with a layer of ∼13 nm at each surface being in the layered AFM phase similar to few-layer CrI3 and the rest in the bulk FM phase. The switching of the bulk moment proceeds through a remnant state with nearly compensated magnetic moment along the c-axis, indicating formation of c-axis domains allowed by a weak interlayer coupling strength in the rhombohedral phase. Our results provide a comprehensive picture on the magnetism in CrI3 and point to the possibility of engineering magnetic heterostructures within the same material.

[Carbon monoxide-an underestimated risk? Awareness, perception, knowledge, and prevention activities]. / Kohlenmonoxid ­ ein unterschätztes Risiko? Bekanntheit, Wahrnehmung, Wissen und Präventionsverhalten.

BACKGROUND: Every year, hospitals in Germany treat roughly 450,000 people in the aftermath of poisoning incidents. To reduce the number of poisoning accidents, it is essential to inform the public about poisoning risks and the possibilities for prevention. OBJECTIVES: The goal was to examine risk perception of poisonings in order to derive insights into adequate communication activities from the results. As a special focus topic, the risk of carbon monoxide poisoning was chosen. METHOD: Telephone interviews were conducted with 1,012 persons aged 14 or over in Germany. They were asked about their awareness, perception, and knowledge of poisoning risks, particularly carbon monoxide. RESULTS: Most people are aware of risks such as accidental intoxications caused by alcohol, carbon monoxide, or mushrooms. Other risks that could be especially dangerous for children, like coin cell batteries, lamp oils, or liquids in e­cigarettes, are less known. Of the interviewees, 82% had already heard of poisoning incidents in connection to carbon monoxide and 41% estimated the risk of accidental carbon monoxide poisoning as rather or very high. However, only 15% had already installed a carbon monoxide detector. Although people are mostly aware of the main causes and identifiers of carbon monoxide poisoning, more than one third still believe that carbon monoxide can be identified by its odor, smoke, or the smoke alarm signal. In addition, there is a special need for information about the risks of carbon monoxide intoxication through indoor shisha smoking and indoor storage of wood pellets. CONCLUSION: The results offer first insights into the target groups and possible dissemination paths for future risk communication activities.

Highly Efficient Spin-Orbit Torque and Switching of Layered Ferromagnet Fe3GeTe2.

Among van der Waals (vdW) layered ferromagnets, Fe3GeTe2 (FGT) is an excellent candidate material to form FGT/heavy metal heterostructures for studying the effect of spin-orbit torques (SOT). Its metallicity, strong perpendicular magnetic anisotropy built in the single atomic layers, relatively high Curie temperature (Tc ∼ 225 K), and electrostatic gate tunability offer a tantalizing possibility of achieving the ultimate high SOT limit in monolayer all-vdW nanodevices. In this study, we fabricate heterostructures of FGT/Pt with 5 nm of Pt sputtered onto the atomically flat surface of ∼15-23 nm exfoliated FGT flakes. The spin current generated in Pt exerts a damping-like SOT on FGT magnetization. At ∼2.5 × 1011 A/m2 current density, SOT causes the FGT magnetization to switch, which is detected by the anomalous Hall effect of FGT. To quantify the SOT effect, we measure the second harmonic Hall responses as the applied magnetic field rotates the FGT magnetization in the plane. Our analysis shows that the SOT efficiency is comparable with that of the best heterostructures containing three-dimensional (3D) ferromagnetic metals and much larger than that of heterostructures containing 3D ferrimagnetic insulators. Such large efficiency is attributed to the atomically flat FGT/Pt interface, which demonstrates the great potential of exploiting vdW heterostructures for highly efficient spintronic nanodevices.

Probing Magnetism in Insulating Cr2Ge2Te6 by Induced Anomalous Hall Effect in Pt.

Two-dimensional ferromagnet Cr2Ge2Te6 (CGT) is so resistive below its Curie temperature that probing its magnetism by electrical transport becomes extremely difficult. By forming heterostructures with Pt, however, we observe clear anomalous Hall effect (AHE) in 5 nm thick Pt deposited on thin (<50 nm) exfoliated flakes of CGT. The AHE hysteresis loops persist to ∼60 K, which matches well to the Curie temperature of CGT obtained from the bulk magnetization measurements. The slanted AHE loops with a narrow opening indicate magnetic domain formation, which is confirmed by low-temperature magnetic force microscopy (MFM) imaging. These results clearly demonstrate that CGT imprints its magnetization in the AHE signal of the Pt layer. Density functional theory calculations of CGT/Pt heterostructures suggest that the induced ferromagnetism in Pt may be primarily responsible for the observed AHE. Our results establish a powerful way of investigating magnetism in 2D insulating ferromagnets, which can potentially work for monolayer devices.

[Is breastfeeding in public socially accepted? : Experiences and attitudes of the general population and breastfeeding mothers]. / Ist Stillen in der Öffentlichkeit gesellschaftlich akzeptiert? : Erfahrungen und Einstellungen der Bevölkerung und stillender Mütter.

BACKGROUND: Despite the undeniable benefits, breastfeeding in public has led in the past to controversies that gained a lot of media coverage. For this reason, the attitudes of the general population towards breastfeeding in public and the experiences of mothers who breastfeed in public were examined. OBJECTIVE: The objectives were to collect current data on the perception and acceptance of breastfeeding in public. MATERIALS AND METHODS: We surveyed 1003 respondents from the general population aged 14 years and over and 306 mothers with children of breastfeeding age on the subject of breastfeeding in public by means of computer-assisted web interviewing. RESULTS: Of mothers, 6% reported that their experiences of breastfeeding in public tended to be rather or very negative. Of the general population sample, 66% held the fundamental opinion that breastfeeding should be possible everywhere at all times, compared to 80% of mothers (p < 0.05). Special differences can be seen for breastfeeding in restaurants and cafes. Although only just under 50% of the population sample approves of breastfeeding in these locations, it is not avoided by the majority of mothers (54%). Overall, knowledge of the benefits of breastfeeding is associated with increased acceptance of breastfeeding in public. No special demographic characteristics were observed for the group of persons with a negative attitude towards breastfeeding in public (6%). CONCLUSIONS: No special target group for improving acceptance of breastfeeding in public can be identified in the population on the basis of the present findings. A conflict potential was identified for certain places and situations, however, which enables the development of strategies to increase acceptance.

Effect of Distance on Photoluminescence Quenching and Proximity-Induced Spin-Orbit Coupling in Graphene/WSe2 Heterostructures.

Spin-orbit coupling (SOC) in graphene can be greatly enhanced by proximity coupling it to transition metal dichalcogenides (TMDs) such as WSe2. We find that the strength of the acquired SOC in graphene depends on the stacking order of the heterostructures when using hexagonal boron nitride ( h-BN) as the capping layer, i.e., SiO2/graphene/WSe2/ h-BN exhibiting stronger SOC than SiO2/WSe2/graphene/ h-BN. We utilize photoluminescence (PL) as an indicator to characterize the interaction between graphene and monolayer WSe2 grown by chemical vapor deposition. We observe much stronger PL quenching in the SiO2/graphene/WSe2/ h-BN stack than in the SiO2/WSe2/graphene/ h-BN stack and, correspondingly, a much larger weak antilocalization (WAL) effect or stronger induced SOC in the former than in the latter. We attribute these two effects to the interlayer distance between graphene and WSe2, which depends on whether graphene is in immediate contact with h-BN. Our observations and hypothesis are further supported by first-principles calculations, which reveal a clear difference in the interlayer distance between graphene and WSe2 in these two stacks.

Pesticide Residues in Food: Attitudes, Beliefs, and Misconceptions among Conventional and Organic Consumers.

Pesticide use and pesticide residues in foods have been the subject of controversial public discussions and media coverage in Germany. Against this background, a better understanding of public risk perceptions is needed to promote efficient public health communication. To this end, this study captures the German public's perception of pesticide residues in foods. A representative sample of the population aged 14 years and older (n = 1,004) was surveyed via computer-assisted telephone interviewing on their attitudes and knowledge with regard to pesticide residues. Based on questions regarding their typical consumer behavior, respondents were classified into conventional and organic consumers to identify differences as well as similarities between these two consumer types. As assessed with an open-ended question, both organic and conventional consumers viewed pesticides, chemicals, and toxins as the greatest threats to food quality and safety. Evaluating the risks and benefits of pesticide use, more than two-thirds of organic consumers (70%) rated the risks as greater than the benefits, compared with just over one-half of conventional consumers (53%). Concern about the detection of pesticide residues in the food chain and bodily fluids was significantly higher among organic compared with conventional consumers. Only a minority of respondents was aware that legal limits for pesticide residues (referred to as maximum residue levels) exist, with 69% of organic and 61% of conventional consumers believing that the presence of pesticide residues in foods is generally not permitted. A lack of awareness of maximum residue levels was associated with heightened levels of concern about pesticide residues. Finally, general exposure to media reporting on pesticide residues was associated with more frequent knowledge of legal limits for pesticide residues, whereas actively seeking information on pesticide residues was not. The possible mechanisms underlying these findings are discussed.

[Perceived risks of food contaminants]. / Risikowahrnehmung von Kontaminanten in Lebensmitteln.

BACKGROUND: Food contaminants can pose a serious health threat. In order to carry out adequate risk communication measures, the subjective risk perception of the public must be taken into account. In this context, the breadth of the topic and insufficient terminological delimitations from residues and food additives make an elaborate explanation of the topic to consumers indispensable. A representative population survey used language adequate for lay people and a clear definition of contaminants to measure risk perceptions with regard to food contaminants among the general public. OBJECTIVES: The study aimed to assess public awareness of contaminants and the perceived health risks associated with them. In addition, people's current knowledge and need for additional information, their attitudes towards contaminants, views on stakeholder accountability, as well as compliance with precautionary measures, such as avoiding certain foods to reduce health risks originating from contaminants, were assessed. MATERIALS AND METHODS: A representative sample of 1001 respondents was surveyed about food contaminants via computer-assisted telephone interviewing. RESULTS: The majority of respondents rated contaminants as a serious health threat, though few of them spontaneously mentioned examples of undesirable substances in foods that fit the scientific or legal definition of contaminants. Mercury and dioxin were the most well-known contaminants. Only a minority of respondents was familiar with pyrrolizidine alkaloids. CONCLUSIONS: The present findings highlight areas that require additional attention and provide implications for risk communication geared to specific target groups.