Theoretical study of impurity-induced magnetism in FeSe

Experimental evidence suggests that FeSe is close to a magnetic instability, and recent scanning tunneling microscopy (STM) measurements on FeSe multilayer films have revealed stripe order locally pinned near defect sites. Motivated by these findings, we perform a theoretical study of locally induced magnetic order near nonmagnetic impurities in a model relevant for FeSe. We find that relatively weak repulsive impurities indeed are capable of generating short-range magnetism, and explain the driving mechanism for the local order by resonant eg-orbital states. In addition, we investigate the importance of orbital-selective self-energy effects relevant for Hund's metals, and show how the structure of the induced magnetization cloud gets modified by orbital selectivity. Finally, we make concrete connection to STM measurements of iron-based superconductors by symmetry arguments of the induced magnetic order, and the basic properties of the Fe Wannier functions relevant for tunneling spectroscopy.Comment: 10 pages, 4 figure

Robustness of Quasiparticle Interference Test for Sign-changing Gaps in Multiband Superconductors

Recently, a test for a sign-changing gap function in a candidate multiband unconventional superconductor involving quasiparticle interference data was proposed. The test was based on the antisymmetric, Fourier transformed conductance maps integrated over a range of momenta $\bf q$ corresponding to interband processes, which was argued to display a particular resonant form, provided the gaps changed sign between the Fermi surface sheets connected by $\bf q$. The calculation was performed for a single impurity, however, raising the question of how robust this measure is as a test of sign-changing pairing in a realistic system with many impurities. Here we reproduce the results of the previous work within a model with two distinct Fermi surface sheets, and show explicitly that the previous result, while exact for a single nonmagnetic scatterer and also in the limit of a dense set of random impurities, can be difficult to implement for a few dilute impurities. In this case, however, appropriate isolation of a single impurity is sufficient to recover the expected result, allowing a robust statement about the gap signs to be made.Comment: 9 pages, 12 figure

Symmetry-forbidden intervalley scattering by atomic defects in monolayer transition-metal dichalcogenides

Intervalley scattering by atomic defects in monolayer transition metal dichalcogenides (TDMs; MX2) presents a serious obstacle for applications exploiting their unique valley-contrasting properties. Here, we show that the symmetry of the atomic defects can give rise to an unconventional protection mechanism against intervalley scattering in monolayer TMDs. The predicted defect-dependent selection rules for intervalley scattering can be verified via Fourier transform scanning tunneling spectroscopy (FT-STS), and provide a unique identification of, e.g., atomic vacancy defects (M vs X). Our findings put the absence of the intervalley FT-STS peak in recent experiments in a different perspective.Comment: 7 pages, 4 figures + supplementary. Published versio

Impurity-induced antiferromagnetic order in Pauli-limited nodal superconductors: application to heavy fermion CeCoIn5

We investigate the properties of the coexistence phase of itinerant antiferromagnetism and nodal $d$-wave superconductivity (Q-phase) discovered in heavy fermion CeCoIn5 under applied magnetic field. We solve the minimal model that includes $d$-wave superconductivity and underlying magnetic correlations in real space to elucidate the structure of the $Q$-phase in the presence of an externally applied magnetic field. We further focus on the role of magnetic impurities, and show that they nucleate the Q-phase at lower magnetic fields. Our most crucial finding is that, even at zero applied field, dilute magnetic impurities cooperate via RKKY-like exchange interactions to generate a long-range ordered coexistence state identical to the Q-phase. This result is in agreement with recent neutron scattering measurements [S. Raymond et al., J. Phys. Soc. Jpn. {\bf 83}, 013707 (2014)].Comment: 7 pages, 7 figure

Phylogenetic conservation of soil bacterial responses to simulated global changes.

Soil bacterial communities are altered by anthropogenic drivers such as climate change-related warming and fertilization. However, we lack a predictive understanding of how bacterial communities respond to such global changes. Here, we tested whether phylogenetic information might be more predictive of the response of bacterial taxa to some forms of global change than others. We analysed the composition of soil bacterial communities from perturbation experiments that simulated warming, drought, elevated CO2 concentration and phosphorus (P) addition. Bacterial responses were phylogenetically conserved to all perturbations. The phylogenetic depth of these responses varied minimally among the types of perturbations and was similar when merging data across locations, implying that the context of particular locations did not affect the phylogenetic pattern of response. We further identified taxonomic groups that responded consistently to each type of perturbation. These patterns revealed that, at the level of family and above, most groups responded consistently to only one or two types of perturbations, suggesting that traits with different patterns of phylogenetic conservation underlie the responses to different perturbations. We conclude that a phylogenetic approach may be useful in predicting how soil bacterial communities respond to a variety of global changes. This article is part of the theme issue 'Conceptual challenges in microbial community ecology'

Ionization of oriented targets by intense circularly polarized laser pulses: Imprints of orbital angular nodes in the 2D momentum distribution

We solve the three-dimensional time-dependent Schr\"{o}dinger equation for a few-cycle circularly polarized femtosecond laser pulse interacting with an oriented target exemplified by an Argon atom, initially in a $3\text{p}_{x}$ or $3\text{p}_{y}$ state. The photoelectron momentum distributions show distinct signatures of the orbital structure of the initial state as well as the carrier-envelope phase of the applied pulse. Our \textit{ab initio} results are compared with results obtained using the length-gauge strong-field approximation, which allows for a clear interpretation of the results in terms of classical physics. Furthermore, we show that ionization by a circularly polarized pulse completely maps out the angular nodal structure of the initial state, thus providing a potential tool for studying orbital symmetry in individual systems or during chemical reactions

Associative Learning from Verbal Action-Effect Instructions: A Replication and Investigation of Underlying Mechanisms

According to the ideomotor principle, repeated experience with an action and its perceivable consequences (effects) establish action-effect associations. Research on verbal instructions indicates that such associations are also acquired from verbal information. In the present experiment (N = 651), first, we aimed to replicate unintentional response-priming effects from verbal action-effect instructions (direct replication; Condition 1). Second, we investigated the involvement of perceptual processes in the verbally induced response-priming effect by perceptually presenting (Condition 1) versus not presenting (Condition 2) the color that was subsequently named as an effect in the instructions. Third, we tested a saliency-based explanation of the verbally induced response-priming effect by highlighting all components (action and effect) without an association between them (Condition 3). Overall, we found the predicted response-priming effect following verbal action-effect instructions (overall conditions and in the replication Condition 1). Condition 2, which did not include perceptual information in the instructions, still showed a significant response-priming effect but was descriptively weaker compared to the effect of the replication Condition 1. Condition 3, which merely highlighted the action and effect component without endorsing an association, did not show a significant effect. In sum, our study provides further solid evidence that verbal instructions lead to unintentional response-priming effects. Other conclusions must be considered preliminary: The between-condition comparisons were descriptively in the predicted direction—perceptual aspects are relevant, and a saliency-based account can be excluded—but the differences in accuracy between conditions were not statistically significant

Dealing with negative stereotypes in sports: the role of cognitive anxiety when multiple identities are activated in sensorimotor tasks

Based on research on stereotype threat and multiple identities, this work explores the beneficial effects of activating a positive social identity when a negative identity is salient on women’s performance in sports. Further, in line with research on the effects of anxiety in sports, we investigate whether the activation of a positive social identity buffers performance from cognitive anxiety associated with a negative stereotype. Two experiments tested these predictions in field settings. Experiment 1 (N = 83) shows that the simultaneous activation of a positive (i.e., member of a soccer team) and a negative social identity (i.e., woman) led to better performance than the activation of only a negative social identity for female soccer players. Experiment 2 (N = 46) demonstrates that identity condition moderated the effect of cognitive anxiety on performance for female basketball players. Results are discussed concerning multiple identities’ potential for dealing with stressful situations

Situational Cues in Thoughts About the Future: Relationships With Self-Reported and Actual Self-Regulation Success

Based on stimulus–response learning accounts, we argue that including situational cues in thought about intended actions is an important aspect of self-regulation success in general and in successfully implementing delayed intentions. Accordingly, in Study 1 (N = 328), we replicate a previous study and show a positive relationship between the self-reported inclusion of situational cues in thoughts about intended actions and beliefs of self-regulation success. In Study 2 (N = 136), we find a similar tendency when measuring self-regulation success with an assigned task to be completed within one week. Our results fit with if-then planning perspectives on how to facilitate novel behavior and recent perspectives that attribute self-regulation success to beneficial habits