A Coplanar Waveguide Resonator Technique for the Characterization of Iron-Based Superconductors

We present in detail a coplanar waveguide resonator (CPWR) method for the characterization of superconducting single crystals. It exploits the region of a CPWR where the rf magnetic field is quite homogeneous, by coupling a sample to it. Measurements are performed with and without the crystal, allowing a cavity perturbation approach. From the modifications in the resonance frequency and quality factor of the system it is possible to extract the London penetration depth and its anisotropy, quasiparticle conductivity, surface impedance and, when a coexisting magnetic phase is present, even bulk complex susceptibility

SHREC'16: partial matching of deformable shapes

Matching deformable 3D shapes under partiality transformations is a challenging problem that has received limited focus in the computer vision and graphics communities. With this benchmark, we explore and thoroughly investigate the robustness of existing matching methods in this challenging task. Participants are asked to provide a point-to-point correspondence (either sparse or dense) between deformable shapes undergoing different kinds of partiality transformations, resulting in a total of 400 matching problems to be solved for each method - making this benchmark the biggest and most challenging of its kind. Five matching algorithms were evaluated in the contest; this paper presents the details of the dataset, the adopted evaluation measures, and shows thorough comparisons among all competing methods

You Can't See Me: Anonymizing Graphs Using the Szemerédi Regularity Lemma.

Complex networks gathered from our online interactions provide a rich source of information that can be used to try to model and predict our behavior. While this has very tangible benefits that we have all grown accustomed to, there is a concrete privacy risk in sharing potentially sensitive data about ourselves and the people we interact with, especially when this data is publicly available online and unprotected from malicious attacks. k-anonymity is a technique aimed at reducing this risk by obfuscating the topological information of a graph that can be used to infer the nodes' identity. In this paper we propose a novel algorithm to enforce k-anonymity based on a well-known result in extremal graph theory, the Szemerédi regularity lemma. Given a graph, we start by computing a regular partition of its nodes. The Szemerédi regularity lemma ensures that such a partition exists and that the edges between the sets of nodes behave almost randomly. With this partition, we anonymize the graph by randomizing the edges within each set, obtaining a graph that is structurally similar to the original one yet the nodes within each set are structurally indistinguishable. We test the proposed approach on real-world networks extracted from Facebook. Our experimental results show that the proposed approach is able to anonymize a graph while retaining most of its structural information

Scaling laws for ion irradiation effects in iron-based superconductors

We report on ion irradiation experiments performed on compounds belonging to the BaFe 2As 2 family, each one involving the partial substitution of an atom of the parent compound (K for Ba, Co for Fe, and P for As), with an optimal composition to maximize the superconducting critical temperature Tc. Employed ion beams were 3.5-MeV protons, 250-MeV Au ions, and 1.2-GeV Pb ions, but additional data from literature are also considered, thus covering a wide range of ions and energies. Microwave characterization based on the use of a coplanar waveguide resonator allowed us to investigate the irradiation-induced Tc degradation, as well as the increase of normal state resistivity and London penetration depth. The damage was quantified in terms of displacements per atom (dpa). From this broad and comprehensive set of experimental data, clear scaling laws emerge, valid in the range of moderate irradiation-induced disorder (dpa up to 5 × 10 - 3 were investigated). In these conditions, linear trends with dpa were found for all the modification rates, while a power law dependence on the ion energy was found for heavy-ion irradiation. All these scaling laws are reported and discussed throughout the paper

Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2

We report on the combined experimental and theoretical analysis of the microwave-frequency electromagnetic response of BaFe2As2single crystals with different substitutions: K in the Ba site (hole doping), Co in the Fe site (electron doping), and P in the As site (isovalent substitution). Measurements using a coplanar resonator technique lead to the experimental determination of the penetration depth and microwave conductivity as a function of temperature. The whole set of data is analyzed within a self-consistent three-bands±-wave Eliashberg approach, able to account for all the main observed features in the different properties. Besides the validation of the model itself, the comparison between experiment and theory allows discussing the possible role of the Fe-As planes in defining the superconducting properties of these compounds, the relevance of coherence effects, and the presence of nodes in the superconducting order parameter

Polynomial-time metrics for attributed trees

We address the problem of comparing attributed trees and propose four novel distance measures centered around the notion of a maximal similarity common subtree. The proposed measures are general and defined on trees endowed with either symbolic or continuous-valued attributes and can be applied to rooted as well as unrooted trees. We prove that our measures satisfythe metric constraints and provide a polynomial-time algorithm to compute them. This is a remarkable and attractive property, since the computation of traditional edit-distance-based metrics is, in general, NP-complete, at least in the unordered case. We experimentally validate the usefulness of our metrics on shape matching tasks and compare them with (an approximation of) edit-distance

Disorder-Driven Transition from s(+/-) to s(+ +) Superconducting Order Parameter in Proton Irradiated Ba(Fe1-xRhx)(2)As-2 Single Crystals

Microwave measurements of the London penetration depth and critical temperature T c were used to show evidence of a disordered-driven transition from s ± to s + + order parameter symmetry in optimally doped Ba ( Fe 1 − x Rh x ) 2 As 2 single crystals, where disorder was induced by means of 3.5 MeV proton irradiation. Signatures of such a transition, as theoretically predicted [V. D. Efremov et al., Phys. Rev. B 84, 180512(R) (2011)], are found as a drop in the low-temperature values of the London penetration depth and a virtually disorder-independent superconducting T c . We show how these experimental observations can be described by multiband Eliashberg calculations in which the effect of disorder is accounted for in a suitable way. To this aim, an effective two-band approach is adopted, allowing us to treat disorder in a range between the Born approximation and the unitary limit

Vortex pinning in Au-irradiated FeSe0.4Te0.6 crystals from the static limit to gigahertz frequencies

Fe(Se,Te) is one of the simplest compounds of iron-based superconductors, but it shows a variety of vortex pinning phenomena both in thin-film and single-crystal forms. These properties are particularly important in light of its potential for applications ranging from the development of coated conductors for high-field magnets to topological quantum computation exploiting the Majorana particles found in the superconducting vortex cores. In this paper, we characterize the pinning properties of FeSe 0.4 Te 0.6 single crystals, both pristine and Au-irradiated, with a set of characterization techniques ranging from the static limit to the GHz frequency range by using dc magnetometry, ac susceptibility measurements of both the fundamental and the third harmonic signals, and by microwave coplanar waveguide resonator measurements of London and Campbell penetration depths. We observed signatures of single vortex pinning that can be modeled by a parabolic pinning potential, dissipation caused by flux creep, and a general enhancement of the critical current density after 320 MeV Au ion irradiation