Universal response of the type-II Weyl semimetals phase diagram

The discovery of Weyl semimetals represents a significant advance in topological band theory. They paradigmatically enlarged the classification of topological materials to gapless systems while simultaneously providing experimental evidence for the long-sought Weyl fermions. Beyond fundamental relevance, their high mobility, strong magnetoresistance, and the possible existence of even more exotic effects, such as the chiral anomaly, make Weyl semimetals a promising platform to develop radically new technology. Fully exploiting their potential requires going beyond the mere identification of materials and calls for a detailed characterization of their functional response, which is severely complicated by the coexistence of surface- and bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl points, respectively. Here, we focus on the type-II Weyl semimetal class where we find a stoichiometry-dependent phase transition from a trivial to a non-trivial regime. By exploring the two extreme cases of the phase diagram, we demonstrate the existence of a universal response of both surface and bulk states to perturbations. We show that quasi-particle interference patterns originate from scattering events among surface arcs. Analysis reveals that topologically non-trivial contributions are strongly suppressed by spin texture. We also show that scattering at localized impurities generate defect-induced quasiparticles sitting close to the Weyl point energy. These give rise to strong peaks in the local density of states, which lift the Weyl node significantly altering the pristine low-energy Weyl spectrum. Visualizing the microscopic response to scattering has important consequences for understanding the unusual transport properties of this class of materials. Overall, our observations provide a unifying picture of the Weyl phase diagram

Research Blogs and the Discussion of Scholarly Information

The research blog has become a popular mechanism for the quick discussion of scholarly information. However, unlike peer-reviewed journals, the characteristics of this form of scientific discourse are not well understood, for example in terms of the spread of blogger levels of education, gender and institutional affiliations. In this paper we fill this gap by analyzing a sample of blog posts discussing science via an aggregator called ResearchBlogging.org (RB). ResearchBlogging.org aggregates posts based on peer-reviewed research and allows bloggers to cite their sources in a scholarly manner. We studied the bloggers, blog posts and referenced journals of bloggers who posted at least 20 items. We found that RB bloggers show a preference for papers from high-impact journals and blog mostly about research in the life and behavioral sciences. The most frequently referenced journal sources in the sample were: Science, Nature, PNAS and PLoS One. Most of the bloggers in our sample had active Twitter accounts connected with their blogs, and at least 90% of these accounts connect to at least one other RB-related Twitter account. The average RB blogger in our sample is male, either a graduate student or has been awarded a PhD and blogs under his own name

Manually assisted body-weight supported locomotor training does not re-establish walking in non-walking subjects with chronic incomplete spinal cord injury: A randomized clinical trial

Objective: To assess the effects of manually assisted body-weight supported locomotor training in subjects with chronic incomplete spinal cord injury. Design: Randomized controlled clinical trial. Subjects: Twenty subjects with American Spinal Injury Association Impairment Scale grades C or D and > 2 years post-injury. Methods: Random allocation to 60 days of body-weight supported locomotor training, or usual care, which might include over-ground walking. Walking function, lower extremity muscle strength and balance were blindly evaluated pre-/post-intervention. Results: A small, non-significant improvement in walking function was observed (0.1 m/s (95% confidence interval (95% CI) –0.2, 0.4)), but subjects without baseline gait function, did not re-establish walking. The effect on lower extremity muscle strength was 2.7 points (95% CI –1.4, 6.8). No difference was observed in balance measures. Conclusion: Subjects with chronic incomplete spinal cord injury without baseline walking function were unable to re-establish gait with manually assisted body-weight supported locomotor training. A modest, non-significant, improvement was found in strength and walking speed. However, due to study recruitment problems, an effect size that was smaller than anticipated, and large functional heterogeneity among study subjects, the effect of late-onset body-weight supported locomotor training is not clear. Future studies should include larger numbers of subjects with less functional loss and greater functional homogeneity. Intensive training should probably start earlier post-injury

Robot-assisted locomotor training did not improve walking function in patients with chronic incomplete spinal cord injury: A randomized clinical trial

Objective: To assess the effects of robot-assisted locomotor training in patients with chronic incomplete spinal cord injury. Design: Randomized single-blind controlled clinical trial. Setting: The intervention site was an outpatient clinic, and pre- and post-evaluations were performed in a rehabilitation hospital. Patients: A total of 24 subjects with American Spinal Injury Association Impairment Scale grades C or D, >?2 years post-injury. Interventions: Subjects were randomized to 60 days of robot-assisted locomotor training, or to usual care. Methods: Walking function, lower extremity muscle strength and balance were assessed single-blinded pre- and post-intervention. Results: After a 9-year recruitment period, only 24 of the planned 30 subjects had been enrolled (mean time since injury 17 (standard deviation (SD) 20) years for all subjects). Walking function, lower extremity muscle strength and balance improved modestly in both groups, with no statistically significant group difference in walking function or muscle strength, whereas postural control declined significantly in the intervention group, compared with controls (p?=?0.03). Conclusion: Late-onset robot-assisted locomotor training did not re-establish independent walking function. A modest, but non-significant, effect was seen on muscle strength and balance. However, significant between-group differences were found only in postural control in the control group

Robust spin-polarized midgap states at step edges of topological crystalline insulators

Topological crystalline insulators are materials in which the crystalline symmetry leads to topologically protected surface states with a chiral spin texture, rendering them potential candidates for spintronics applications. Using scanning tunneling spectroscopy, we uncover the existence of one-dimensional (1D) midgap states at odd-atomic surface step edges of the three-dimensional topological crystalline insulator (Pb,Sn)Se. A minimal toy model and realistic tight-binding calculations identify them as spin-polarized flat bands connecting two Dirac points. This nontrivial origin provides the 1D midgap states with inherent stability and protects them from backscattering. We experimentally show that this stability results in a striking robustness to defects, strong magnetic fields, and elevated temperature

Superparamagnetism-induced mesoscopic electron focusing in topological insulators

Recently it has been shown that surface magnetic doping of topological insulators induces backscattering of Dirac states which are usually protected by time-reversal symmetry [Sessi, Nat. Commun. 5, 5349 (2014)10.1038/ncomms6349]. Here we report on quasiparticle interference measurements where, by improved Fermi level tuning, strongly focused interference patterns on surface Mn-doped Bi2Te3 could be directly observed by means of scanning tunneling microscopy at 4 K. Ab initio and model calculations reveal that their mesoscopic coherence relies on two prerequisites: (i) a hexagonal Fermi surface with large parallel segments (nesting) and (ii) magnetic dopants which couple to a high-spin state. Indeed, x-ray magnetic circular dichroism shows superparamagnetism even at very dilute Mn concentrations. Our findings provide evidence of strongly anisotropic Dirac-fermion-mediated interactions and demonstrate how spin information can be transmitted over long distances, allowing the design of experiments and devices based on coherent quantum effects in topological insulators

Superparamagnetism-induced mesoscopic electron focusing in topological insulators

Recently it has been shown that surface magnetic doping of topological insulators induces backscattering of Dirac states which are usually protected by time-reversal symmetry [Sessi et al., Nat. Commun. 5, 5349 (2014)]. Here we report on quasiparticle interference measurements where, by improved Fermi level tuning, strongly focused interference patterns on surface Mn-doped Bi2Te3 could be directly observed by means of scanning tunneling microscopy at 4 K. Ab initio and model calculations reveal that their mesoscopic coherence relies on two prerequisites: (i) a hexagonal Fermi surface with large parallel segments (nesting) and (ii) magnetic dopants which couple to a high-spin state. Indeed, x-ray magnetic circular dichroism shows superparamagnetism even at very dilute Mn concentrations. Our findings provide evidence of strongly anisotropic Dirac-fermion-mediated interactions and demonstrate how spin information can be transmitted over long distances, allowing the design of experiments and devices based on coherent quantum effects in topological insulators

Superparamagnetism-induced mesoscopic electron focusing in topological insulators

Recently it has been shown that surface magnetic doping of topological insulators induces backscattering of Dirac states which are usually protected by time-reversal symmetry [Sessi et al., Nat. Commun. 5, 5349 (2014)]. Here we report on quasiparticle interference measurements where, by improved Fermi level tuning, strongly focused interference patterns on surface Mn-doped Bi2Te3 could be directly observed by means of scanning tunneling microscopy at 4 K. Ab initio and model calculations reveal that their mesoscopic coherence relies on two prerequisites: (i) a hexagonal Fermi surface with large parallel segments (nesting) and (ii) magnetic dopants which couple to a high-spin state. Indeed, x-ray magnetic circular dichroism shows superparamagnetism even at very dilute Mn concentrations. Our findings provide evidence of strongly anisotropic Dirac-fermion-mediated interactions and demonstrate how spin information can be transmitted over long distances, allowing the design of experiments and devices based on coherent quantum effects in topological insulators