Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals

The London penetration depth, $\lambda(T)$, has been measured in several single crystals of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$. Thermodynamic, electromagnetic, and structural characterization measurements confirm that these crystals are of excellent quality. The observed low temperature variation of $\lambda(T)$ follows a power-law, $\Delta \lambda (T) \sim T^n$ with $n=2.4 \pm 0.1$, indicating the existence of normal quasiparticles down to at least $0.02T_c$. This is in contrast to recent penetration depth measurements on single crystals of NdFeAsO$_{1-x}$F$_x$ and SmFeAsO$_{1-x}$F$_x$, which indicate an anisotropic but nodeless gap. We propose that a more three-dimensional character in the electronic structure of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ may lead to an anisotropic $s-$wave gap with point nodes that would explain the observed $\lambda(T)$.Comment: 4 page

Non-exponential London penetration depth in RFeAsO0.9_{0.9}F0.1_{0.1} (R=La,Nd) single crystals

The superconducting penetration depth, $\lambda(T)$, has been measured in RFeAsO$_{0.9}$F$_{0.1}$ (R=La,Nd) single crystals (R-1111). In Nd-1111, we find an upturn in $\lambda(T)$ upon cooling and attribute it to the paramagnetism of the Nd ions, similar to the case of the electron-doped cuprate Nd-Ce-Cu-O. After the correction for paramagnetism, the London penetration depth variation is found to follow a power-law behavior, $\Delta \lambda_L(T)\propto T^{2}$ at low temperatures. The same $T^2$ variation of $\lambda(T)$ was found in non-magnetic La-1111 crystals. Analysis of the superfluid density and of penetration depth anisotropy over the full temperature range is consistent with two-gap superconductivity. Based on this and on our previous work, we conclude that both the RFeAsO (1111) and BaFe$_2$As$_2$ (122) families of pnictide superconductors exhibit unconventional two-gap superconductivity.Comment: v2 is the same as v1 - error in the arxiv submissio

The Lectures, Witte de With, 1992

The publication of four lectures and two debates presented in conjunction with the 1992 Witte de With exhibition programme includes 14 authors' critical analyzes on the following topics: Brazilian artist Oiticica, representation and history, the depiction of the human figure, the art catalogue, graphic design/typography, and the interests of the centre itself. Contains listing of exhibitions and publications. Biographical notes on authors. 62 bibl. ref

Unconventional London Penetration Depth in Single-Crystal Ba(Fe0.93Co0.07)(2)As-2 Superconductors

The London penetration depth lambda(T) has been measured in single crystals of Ba(Fe0.93Co0.07)(2)As-2. The observed low-temperature variation of lambda(T) follows a power law, Delta lambda(T)similar to T-n with n approximate to 2.4 +/- 0.1, indicating the existence of normal quasiparticles down to at least 0.02T(c). This is in contrast with previous penetration depth measurements on single crystals of NdFeAsO1-xFx and SmFeAsO1-xFx, which indicate an anisotropic but nodeless gap. We discuss possible explanations of the observed power law behavior.This article is published as Gordon, R. T., N. Ni, C. Martin, M. A. Tanatar, M. D. Vannette, H. Kim, G. D. Samolyuk et al. "Unconventional London penetration depth in single-crystal Ba (Fe 0.93 Co 0.07) 2 As 2 superconductors." Physical Review Letters 102, no. 12 (2009): 127004. DOI: 10.1103/PhysRevLett.102.127004. Copyright 2009 American Physical Society. Posted with permission

Spatial Rule-Based Modeling: A Method and Its Application to the Human Mitotic Kinetochore

A common problem in the analysis of biological systems is the combinatorial explosion that emerges from the complexity of multi-protein assemblies. Conventional formalisms, like differential equations, Boolean networks and Bayesian networks, are unsuitable for dealing with the combinatorial explosion, because they are designed for a restricted state space with fixed dimensionality. To overcome this problem, the rule-based modeling language, BioNetGen, and the spatial extension, SRSim, have been developed. Here, we describe how to apply rule-based modeling to integrate experimental data from different sources into a single spatial simulation model and how to analyze the output of that model. The starting point for this approach can be a combination of molecular interaction data, reaction network data, proximities, binding and diffusion kinetics and molecular geometries at different levels of detail. We describe the technique and then use it to construct a model of the human mitotic inner and outer kinetochore, including the spindle assembly checkpoint signaling pathway. This allows us to demonstrate the utility of the procedure, show how a novel perspective for understanding such complex systems becomes accessible and elaborate on challenges that arise in the formulation, simulation and analysis of spatial rule-based models