Emergence of novel magnetic order at finite temperature in overdoped pnictides

We examine the temperature dependence of the magnetic ordering in the frustrated Heisenberg $J_1-J_2$ model in presence of two different kind of dopants: vacancies or magnetic impurities. We demonstrate that, irrespective to their magnetic ratio, the introduction of impurities quenches the order by disorder selection mechanism associated with an Ising-like phase transition at low temperatures and gives way to a $90^\circ$ (anticollinear) order . The presence of dopants triggers a non trivial competition between entropically selected states (collinear) and energetically favoured ones (anticollinear) in dependence of both dilution and temperature. While in case of magnetic impurity, the interesting magnetic phases are observed for full range of temperature and doping, in case of nonmagnetic impurities every magnetic order is destroyed at all temperatures above $12\%$ dilution. At fixed low temperature and tuning the doping we show a first order phase transition leading to the re-entrance of the Ising-like order with percolation of islands of $90^\circ$ order. At fixed doping and varying the temperature we observe a transition from the anticollinear to the collinear phase assisted by a new emerging magnetic phase in the presence of magnetic impurities, whilst in case of vacancies this transition is characterised by a coexistent region of both. Furthermore, tuning the magnetic moment of the impurities, a complete collapse of the Ising-like order is attained. This is in agreement with observations of Ir dopant atoms in superconducting Ba(Fe$_{1-x}$Ir$_x$)$_2$As$_2$ with $x<0.047$

Large scale Micro-Photometry for high resolution pH-characterization during electro-osmotic pumping and modular micro-swimming

Micro-fluidic pumps as well as artificial micro-swimmers are conveniently realized exploiting phoretic solvent flows based on local gradients of temperature, electrolyte concentration or pH. We here present a facile micro-photometric method for monitoring pH gradients and demonstrate its performance and scope on different experimental situations including an electro-osmotic pump and modular micro-swimmers assembled from ion exchange resin beads and polystyrene colloids. In combination with the present microscope and DSLR camera our method offers a 2 \mu m spatial resolution at video frame rate over a field of view of 3920x2602 \mu m^2. Under optimal conditions we achieve a pH-resolution of 0.05 with about equal contributions from statistical and systematical uncertainties. Our quantitative micro-photometric characterization of pH gradients which develop in time and reach out several mm is anticipated to provide valuable input for reliable modeling and simulations of a large variety of complex flow situations involving pH-gradients including artificial micro-swimmers, microfluidic pumping or even electro-convection.Comment: 5 figures, 15 page

Highly-efficient state-selective sub-microsecond photoionization detection of single atoms

We experimentally demonstrate a detection scheme suitable for state analysis of single optically trapped atoms in less than 1 {\mu}s with an overall detection efficiency {\eta} exceeding 98%. The method is based on hyperfine-state-selective photoionization and subsequent registration of the correlated photoion-electron pairs by coincidence counting via two opposing channel electron multipliers. The scheme enables the calibration of absolute detection efficiencies and might be a key ingredient for future quantum information applications or precision spectroscopy of ultracold atoms.Comment: 4 pages, 4 figure

The ICT Revolution and Preferences for Taxing Top Earners

How has the ICT-driven transformation of labour markets in recent decades affected redistributive preferences? We move beyond existing research by focusing on the ‘winners’ of the ICT revolution and on other-regarding preferences for taxing top earners. We carry out an interactive, online experiment with around 3,000 US respondents to test whether fairness perceptions and redistributive preferences differ when top incomes are gained through luck, routine work, or complex work. This set up aims to mirror the changing nature of tasks performed by high-earning workers in the US labour market as a result of the ICT revolution. We find that the desired tax rate on top earners is up to 5.3 percentage points lower for the complex work than the routine work treatment, and that high incomes from complex work are perceived as fairer and more deserved. A follow-up vignettes study then provides strong evidence that high earning jobs are perceived to be more complex. Taken together, our findings highlight an important and previously under-explored channel through which the ICT revolution may have dampened demand for progressive taxation in the advanced democracies

Computer simulation of defects and oxygen transport in yttria-stabilized zirconia

We have used molecular dynamics simulations and energy minimization calculations to examine defect energetics and oxygen diffusion in yttria-stabilized zirconia (YSZ). Oxygen vacancies prefer to be second nearest neighbors to yttrium dopants. The oxygen diffusion coefficient shows a peak at 8 mol% yttria consistent with experimental findings. The activation energy for oxygen diffusion varies from 0.6 to 1.0 eV depending on the yttria content. The YZr' VO YZr' complex with a binding energy of -0.85 eV may play an important role in any conductivity degradation of YSZ

TALKING INSTITUTIONS IN THE SHARING ECONOMY: A CONTENT ANALYSIS OF ACTOR QUOTES IN THE PRINT MEDIA AND A TAXONOMY OF DISCURSIVE STRATEGIES

We study how actors engage in institutional work to manage legitimacy by influencing media discourse in the face of discontinuous innovation. We content-analyze actor quotes reproduced in newspaper articles about the ‘sharing economy’ in the taxi and lodging industries to survey this aspect of media discourse and offer a taxonomy of the discursive strategies used in the public debate on institutional change. We find that actor quotes are dominantly from offensive actors striving for institutional change, mostly due to a relatively low share of voice of incumbent firms as defensive actors aiming at institutional maintenance. Whereas offensive actors aimed for legitimacy in their discursive strategies by balancing attacks on existing institutions with assertions of new institutions, defensive actors aimed for legitimacy more by attacking new institutions than by reinforcing existing ones. Our findings suggest that, contrary to prior beliefs, preventing the emergence of new institutions plays a crucial role for defensive institutional work