Dynamic norms for dynamic times? An experiment on the effects of dynamic and static norms messages on COVID-19 vaccination intention

Social norms messages may motivate COVID-19 preventive behaviors, such as getting vaccinated. To date, however, the research has mainly focused on the established concept of static norms and widely ignored the potential of dynamic norms. Dynamic norms convey information about how norms are developing over time and have been shown to promote change when the behavior is not yet the majority norm. The present study investigated the potential of dynamic norms in the context of the COVID-19 vaccination campaign. It examined (a) the effects of static and dynamic norms messages on vaccination intention, (b) the mechanisms through which dynamic norms may influence vaccination intention, and (c) the potential of dynamic norms to increase vaccination intention of vaccine-hesitant people. We conducted a preregistered online experiment with three conditions (static norm, dynamic norm, control message) among people who were not yet vaccinated (N = 2,289, 16-60 years) in May 2021, during the early vaccine roll-out period for the general population in Switzerland. We found no effects of exposure to the static or dynamic norms messages on vaccination intention and no specific influence mechanisms of dynamic norms (e.g., via perceived future norm) - neither for participants who were willing to get vaccinated nor for the vaccine-hesitant group. However, further analyses showed that, among vaccine-hesitant participants, the normative perception that formerly vaccine-critical people were changing their minds was correlated with a stronger vaccination intention. We discuss potential reasons why social norms messages did not show an effect in our study and derive theoretical and practical implications

Reasons for not getting vaccinated against COVID-19 in German-speaking Switzerland: An online survey among vaccine hesitant 16-60 year olds

Background: Several research studies have examined the reasons why people are hesitant to be vaccinated against COVID-19. However, there is no published data to date on Switzerland. Identifying these reasons among the Swiss population who are vaccine hesitant may help inform campaigns to encourage vaccine confidence. Aims: The primary aim of this study is to identify the reasons for not getting vaccinated against COVID-19 among Swiss residents who are vaccine hesitant. The secondary aim is to examine whether reasons differ by age, gender, education, and likelihood of accepting a vaccination to better target campaigns and design interventions. Design: An online survey asked participants to indicate the reasons why they were hesitant to be vaccinated against COVID-19. Setting: German-speaking Swiss Cantons, the survey was administered online between 5 May 2021 and 16 May 2021. Participants: The participants in this analysis were a sample of (N=1191) Swiss residents age 16-60 years old from German-speaking Cantons, who could answer an online survey in German, who had yet not been vaccinated, who had not yet registered for a vaccination appointment, and who did not indicate that they would definitely be vaccinated if offered the chance. Findings: Among people who are vaccine hesitant in Switzerland, the most common reasons forbeing hesitant were side-effect, safety, and effectiveness concerns. It was also common for people to indicate that they were healthy/at low risk, would decide later, and that they wanted to build immunity naturally. Less common, but still prevalent concerns included wanting more information, thinking COVID-19 was not a real threat, and concerns that the vaccine may serve another purpose. Differences in reasons for being vaccine hesitant were found by age, gender, education, and likelihood of accepting a vaccination if offered. Conclusions: To increase the likelihood of accepting a vaccination, vaccination campaigns should address side-effect, safety, and effectiveness concerns. Campaigns could also consider informing people why it is necessary for people in lower risk groups to be vaccinated, and why vaccination is preferable to infection for building immunity. While campaigns may be effective in reaching some of the population, alternative strategies might be necessary to strengthen the trust relationship with vaccines and vaccine providers in some groups. Less prevalent concerns, such as not liking needles, could be addressed through individual level interventions

COVID-19 vaccination and changes in preventive behaviours: findings from the 2021 vaccine roll-out in Switzerland

Background: Behavioural, environmental, social and systems interventions (BESSIs) remain important for controlling the COVID-19 pandemic in addition to vaccination. However, people’s adoption of BESSIs may decrease as vaccination rates increase due to reductions in the perceived threat of disease, and changes in risk perceptions of behaviours that increase the chance of infection. Thus, we examined predictors of and changes over time in reports of mask wearing and physical distancing and whether changes in mask wearing and physical distancing differed by vaccination status during the main 2021 COVID-19 vaccine roll-out period in Switzerland. Methods: Weekly online cross-sectional surveys (26 April 2021 to 1 August 2021) among people 18–79 years old in Switzerland, N = 6308 observations and 5511 cases. Logistic regression models using generalized estimating equations. Results: Reports of being vaccinated increased, while mask wearing and physical distancing decreased over time. This decrease was similar regardless of vaccination status. However, the level of reported mask wearing and physical distancing remained higher among vaccinated people. Older, female, and Italian language region respondents also had higher odds of reporting mask wearing and physical distancing. Conclusions: Adoption of COVID-19 preventive behaviours is associated with demographics and vaccination status. Further research is needed to understand the reasons why people who are not vaccinated are less likely to adopt preventive behaviours, including that they may have fewer social and environmental opportunities to do so

Similar zone-center gaps in the low-energy spin-wave spectra of NaFeAs and BaFe2As2

We report results of inelastic-neutron-scattering measurements of low-energy spin-wave excitations in two structurally distinct families of iron-pnictide parent compounds: Na(1-{\delta})FeAs and BaFe2As2. Despite their very different values of the ordered magnetic moment and N\'eel temperatures, T_N, in the antiferromagnetic state both compounds exhibit similar spin gaps of the order of 10 meV at the magnetic Brillouin-zone center. The gap opens sharply below T_N, with no signatures of a precursor gap at temperatures between the orthorhombic and magnetic phase transitions in Na(1-{\delta})FeAs. We also find a relatively weak dispersion of the spin-wave gap in BaFe2As2 along the out-of-plane momentum component, q_z. At the magnetic zone boundary (q_z = 0), spin excitations in the ordered state persist down to 20 meV, which implies a much smaller value of the effective out-of-plane exchange interaction, J_c, as compared to previous estimates based on fitting the high-energy spin-wave dispersion to a Heisenberg-type model.Comment: 5 pages, 4 figures, 1 tabl

Mn local moments prevent superconductivity in iron-pnictides Ba(Fe 1-x Mn x)2As2

75As nuclear magnetic resonance (NMR) experiments were performed on Ba(Fe1-xMnx)2As2 (xMn = 2.5%, 5% and 12%) single crystals. The Fe layer magnetic susceptibility far from Mn atoms is probed by the75As NMR line shift and is found similar to that of BaFe2As2, implying that Mn does not induce charge doping. A satellite line associated with the Mn nearest neighbours (n.n.) of 75As displays a Curie-Weiss shift which demonstrates that Mn carries a local magnetic moment. This is confirmed by the main line broadening typical of a RKKY-like Mn-induced staggered spin polarization. The Mn moment is due to the localization of the additional Mn hole. These findings explain why Mn does not induce superconductivity in the pnictides contrary to other dopants such as Co, Ni, Ru or K.Comment: 6 pages, 7 figure

Phase diagram of iron-arsenide superconductors Ca(Fe1-xCox)2As2 (0 <= x <= 0.2)

Platelet-like single crystals of the Ca(Fe1-xCox)2As2 series having lateral dimensions up to 15 mm and thickness up to 0.5 mm were obtained from the high temperature solution growth technique using Sn flux. Upon Co doping, the c-axis of the tetragonal unit cell decreases, while the a-axis shows a less significant variation. Pristine CaFe2As2 shows a combined spin-density-wave and structural transition near T = 166 K which gradually shifts to lower temperatures and splits with increasing Co-doping. Both transitions terminate abruptly at a critical Co-concentration of xc = 0.075. For x \geq 0.05, superconductivity appears at low temperatures with a maximum transition temperature TC of around 20 K. The superconducting volume fraction increases with Co concentration up to x = 0.09 followed by a gradual decrease with further increase of the doping level. The electronic phase diagram of Ca(Fe1-xCox)2As2 (0 \leq x \leq 0.2) series is constructed from the magnetization and electric resistivity data. We show that the low-temperature superconducting properties of Co-doped CaFe2As2 differ considerably from those of BaFe2As2 reported previously. These differences seem to be related to the extreme pressure sensitivity of CaFe2As2 relative to its Ba counterpart.Comment: 27 pages, 13 figures, articl

Conformity of spin fluctuations in alkali-metal iron selenide superconductors inferred from the observation of a magnetic resonant mode in K(x)Fe(2-y)Se(2)

Spin excitations stemming from the metallic phase of the ferrochalcogenide superconductor K(0.77)Fe(1.85)Se(2) (T_c=32 K) were mapped out in the ab plane by means of the time-of-flight neutron spectroscopy. We observed a magnetic resonant mode at Q_res=(1/2 1/4), whose energy and in-plane shape are almost identical to those in the related compound Rb(0.8)Fe(1.6)Se(2). This lets us infer that there is a unique underlying electronic structure of the bulk superconducting phase K(x)Fe(2)Se(2), which is universal for all alkali-metal iron selenide superconductors and stands in contrast to the doping-tunable phase diagrams of the related iron pnictides. Furthermore, the spectral weight of the resonance on the absolute scale, normalized to the volume fraction of the superconducting phase, is several times larger than in optimally doped BaFe(2-x)Co(x)As(2). We also found no evidence for any additional low-energy branches of spin excitations away from Q_res. Our results provide new input for theoretical models of the spin dynamics in iron based superconductors

KxFe2-ySe2 single crystals: Floating-zone growth, Transport and Structural properties

Single crystals of superconducting KxFe2-ySe2 have been grown with the optical floating-zone technique under application of 8 bar of argon pressure. We found that large and high quality single crystals with dimensions of ~\varnothing6 \times 10 mm could be obtained at the termination of the grown ingot through quenching, while the remaining part of the ingot decomposed. As-grown single crystals commonly represent an intergrowth of two sets of the c-axis characterized by slightly different lattice constants. Single crystal of K0.80Fe1.81Se2 shows a superconducting transition at Tc = 31.6 K, leading to a near 100% expulsion of the external magnetic field in magnetization measurements. On the other hand, neutron-diffraction data indicate that superconductivity in the sample coexists with a iron-vacancy superstructure and static antiferromagnetic order. The anisotropic ratio of the upper critical field Hc2 for both H//c and H//ab configurations is \sim3.46

Superconducting fluctuation corrections to ultrasound attenuation in layered superconductors

We consider the temperature dependence of the sound attenuation and sound velocity in layered impure metals due to superconducting fluctuations of the order parameter above the critical temperature. We obtain the dependence on material properties of these fluctuation corrections in the hydrodynamic limit, where the electron mean free path is much smaller than the wavelength of sound and where the electron collision rate is much larger than the sound frequency. For longitudinal sound propagating perpendicular to the layers, the open Fermi surface condition leads to a suppression of the divergent contributions to leading order, in contrast with the case of paraconductivity. The leading temperature dependent corrections, given by the Aslamazov-Larkin, Maki-Thompson and density of states terms, remain finite as T->Tc. Nevertheless, the sensitivity of new ultrasonic experiments on layered organic conductors should make these fluctuations effects measurable.Comment: 13 pages, 6 figures. Accepted for PRB. Added discussion on incoherent interlayer tunneling and other small modifications suggested by referee