Time-reversal and rotation symmetry breaking superconductivity in Dirac materials

We consider mixed symmetry superconducting phases in Dirac materials in the odd parity channel, where pseudoscalar and vector order parameters can coexist due to their similar critical temperatures when attractive interactions are of finite range. We show that the coupling of these order parameters to unordered magnetic dopants favors the condensation of novel time-reversal symmetry breaking (TRSB) phases, characterized by a condensate magnetization, rotation symmetry breaking, and simultaneous ordering of the dopant moments. We find a rich phase diagram of mixed TRSB phases characterized by peculiar bulk quasiparticles, with Weyl nodes and nodal lines, and distinctive surface states. These findings are consistent with recent experiments on Nb$_x$Bi$_2$Se$_3$ that report evidence of point nodes, nematicity, and TRSB superconductivity induced by Nb magnetic moments.Comment: 11 pages, 2 figure

Competition, efficiency and collective behavior in the "El Farol" bar model

The El Farol bar model, proposed to study the dynamics of competition of agents in a variety of contexts (W. B. Arthur, Amer. Econ. Assoc. Pap. and Proc. 84, 406 (1994)) is studied. We characterize in detail the three regions of the phase diagram (efficient, inefficient and better than random) of the simplest version of the model (D. Challet and Y.-C. Zhang, Physica A, 246, 407 (1997)). The efficient region is shown to have a rich structure, which is investigated in some detail. Changes in the payoff function enhance further the tendency of the model towards a wasteful distribution of resources.Comment: 7 pages Latex, 7 Postscript figures; changed reference, acknowledgments included. Accepted for publication in Europen Physics Journal

Gauge fields, ripples and wrinkles in graphene layers

We analyze elastic deformations of graphene sheets which lead to effective gauge fields acting on the charge carriers. Corrugations in the substrate induce stresses, which, in turn, can give rise to mechanical instabilities and the formation of wrinkles. Similar effects may take place in suspended graphene samples under tension.Comment: contribution to the special issue of Solid State Communications on graphen

Employees\u27 cognitive load and performance during multitasking use of Information Technology

Multitasking-based use of Information Technology, a term that we label MUIT, to accomplish work-related tasks has become a common behavior for employees in organizations. Despite this reality, most research to date has focused on studying either the use of one IT at a time or multi-tasking behaviors in experimental laboratory settings. As a result, this study aims to fill these gaps. Building upon cognitive load theory and multiple resource theory, this paper theorizes that MUIT positively influences cognitive load, which in turn, has a curvilinear (concave, in-verted U) relation with performance. In order to test our hypotheses, we employed the Experi-ence Sampling Method (ESM), a special form of diary study, to gather data on employees at multiple occasions for two weeks. The collected data are hierarchical (multiple observations within individuals), and thus, we employed multi-level regression to test the hypotheses. Results show, as hypothesized, a positive relation between MUIT and cognitive load, and an inverted U relation between cognitive load and performance. Therefore, this study demonstrates that in work settings although MUIT increases cognitive load, cognitive load is not always detrimental: some cognitive load has positive effects on performance until it reaches a tipping point where performance starts to suffer