Critical behavior of Ginzburg-Landau model coupled to massless Dirac fermions

We point out interesting effects of additional massless Dirac fermions with N_F colors upon the critical behavior of the Ginzburg-Landau model. For increasing N_F, the model is driven into the type II regime of superconductivity. The critical exponents are given as a function of N_F.Comment: RevTex4, 4 pages, 1 figure; author information and latest update to this paper at http://www.physik.fu-berlin.de/~kleinert/institution.html; version 2: new references and comments on chiral symmetry breaking adde

The order of the metal to superconductor transition

We present results from large-scale Monte Carlo simulations on the full Ginzburg-Landau (GL) model, including fluctuations in the amplitude and the phase of the matter-field, as well as fluctuations of the non-compact gauge-field of the theory. {}From this we obtain a precise critical value of the GL parameter \kct separating a first order metal to superconductor transition from a second order one, \kct = (0.76\pm 0.04)/\sqrt{2}. This agrees surprisingly well with earlier analytical results based on a disorder theory of the superconductor to metal transition, where the value \kct=0.798/\sqrt{2} was obtained. To achieve this, we have done careful infinite volume and continuum limit extrapolations. In addition we offer a novel interpretation of \kct, namely that it is also the value separating \typeI and \typeII behaviour.<Comment: Minor corrections, present version accepted for publication in PR

Critical properties of the topological Ginzburg-Landau model

We consider a Ginzburg-Landau model for superconductivity with a Chern-Simons term added. The flow diagram contains two charged fixed points corresponding to the tricritical and infrared stable fixed points. The topological coupling controls the fixed point structure and eventually the region of first order transitions disappears. We compute the critical exponents as a function of the topological coupling. We obtain that the value of the $\nu$ exponent does not vary very much from the XY value, $\nu_{XY}=0.67$. This shows that the Chern-Simons term does not affect considerably the XY scaling of superconductors. We discuss briefly the possible phenomenological applications of this model.Comment: RevTex, 7 pages, 8 figure

Implications evinced by the phase diagram, anisotropy, magnetic penetration depths, isotope effects and conductivities of cuprate superconductors

Anisotropy, thermal and quantum fluctuations and their dependence on dopant concentration appear to be present in all cuprate superconductors, interwoven with the microscopic mechanisms responsible for superconductivity. Here we review anisotropy, in-plane and c-axis penetration depths, isotope effect and conductivity measurements to reassess the universal behavior of cuprates as revealed by the doping dependence of these phenomena and of the transition temperature.Comment: 14 pages, 13 figure

Phase Diagram of Superconductors from Non-Perturbative Flow Equations

The universal behaviour of superconductors near the phase transition is described by the three-dimensional field theory of scalar quantum electrodynamics. We approximately solve the model with the help of non-perturbative flow equations. A first- or second-order phase transition is found depending on the relative strength of the scalar versus the gauge coupling. The region of a second-order phase transition is governed by a fixed point of the flow equations with associated critical exponents. We also give an approximate description of the tricritical behaviour and briefly discuss the crossover relevant for the onset of scaling near the critical temperature. Final confirmation of a second-order transition for strong type-II superconductors requires further analysis with extended truncations of the flow equations.Comment: 40 pp + 10 figures in uuencoded file. Final version as it will appear in Phys. Rev.

Applying the traffic safety culture approach in low- and middle-income countries

The Traffic Safety Culture (TSC) approach has been applied primarily in high-income countries (HICs), yet the great majority of the burden of road trauma falls on low- and middle-income countries (LMICs), where it con¬stitutes a humanitarian crisis. The UN Decade of Action for Road Safety established road safety in LMICs as a priority issue and launched a plan to address it. Road safety has subsequently been incorporated into the interna¬tional development agenda via the Sustainable Development Goals. Characteristics of road user behavior, governance, infrastructure, enforce¬ment, and health services in LMICs have led to assertions that many lack a âœsafety cultureâ or, more specifically, a âœtraffic safety culture.â While this invites the suggestion that a TSC approach would have value in LMICs, the question raised in this chapter is whether a psychosocial approach like TSC, developed and applied in HICs, is transferable to LMICs. This is first explored by examining the critique of the assumption that commonly stud¬ied psychological processes are universal, noting examples that are relevant to road safety. Cross-cultural psychology studies show that some of the psy-chological processes commonly studied in HICs differ in important ways in LMICs, while broader comparative research based on anthropology and sociology demonstrates the important influence of religious and cultural factors, economic and infrastructure conditions, institutional capacity and governance. The sociological construct of governmentality provides insight into why public compliance with traffic safety law may be lower in LMICs, and why this situation is likely to take a protracted period of time to change. Given the broader context of road safety in LMICs, the Road Safety Space Model (RSSM) provides a useful framework for identifying the economic, institutional, social, and cultural factors that influence a particular road safety issue in a particular country. This has implications for methodological approaches to TSC in LMICs, as less structured, more ethnographic methods are arguably more appropriate. An analysis of a typ¬ical TSC model, drawing on research from LMICs, demonstrates that the model assumes a particular hierarchy of elements (values, behavioral beliefs, normative beliefs, prototypical image, control beliefs), and relation¬ships between them, which may not be true in LMICs. It is therefore more challenging to apply TSC in LMICs, particularly making the transition from identification of the TSC values and beliefs that lead to behavior to the development of an intervention to bring about changes in behavior. TSC is undoubtedly a promising approach in LMICs; however, its first steps should incorporate qualitative approaches and recognize the wide range of factors that are relevant to TSC; use of the RSSM would facilitate such a process. There is scope for further research to refine models of TSC, to determine the best mix of methods to use, and to explore the role of gov-ernmentality and its implications for TSC. In the interim, practitioners should strive to understand and take into account the broader social and cultural factors that influence behavior in the particular LMIC where they are working.</p