Reversible magnetization below Tc in high-quality superconducting ceramics

International audienceWe have investigated the reversible magnetization below Tc in high-quality YBa2Cu307_d (Y-123), YBa2Cu4Os (Y-124), Y2Ba4Cu7O15+x (Y-247) and Bi2Sr2CaCu2O8+x (Bi-2212), Tl2Ba2Cu106+d (Tl-2201) and Tl2Ba2CalCu2O8+d (T1-2212) ceramics. Except for the stoichiometric Y-124 phase, the oxygen concentration was optimized in order to obtain the highest value of the critical temperature for which the normal-state susceptibility becomes temperature independent. Using the simple London model, we are able to fit the reversible magnetization M(T, H) outside the region near Tc with good accuracy for the nearly three-dimensional YBaCuO phases. For the very anisotropic BiSrCaCuO and TlBaCaCuO phases, we have to include an additional term to take into account the fluctuations of vortices. An important result is that Y-123 exhibits a critical field clearly higher than those of the BiSrCaCuO or TlBaCaCuO phases. We obtain for the Y-123 phase a slope at Tc μodHC2,C/dT = -4.3 T/K and an extrapolated μoHC2,C (0) = 280 T

Magnetic Field Induced Redistribution of Exciton-Polariton Density on Confined Modes

The influence of magnetic field on confined exciton-polariton modes inside a semiconductor microcavity is discussed. The three-dimensional confinement for exciton-polaritons is achieved by the mesa structures confining the photonic part of polaritons. We observe a strong increase of the polariton emission intensity and we argue that this effect is due to the change of the oscillator strength of the excitonic component of polaritons and the change of the excitonic content in polariton state as the magnetic field increases

Scaling of the Equilibrium Magnetization in the Mixed State of Type-II Superconductors

We discuss the analysis of mixed-state magnetization data of type-II superconductors using a recently developed scaling procedure. It is based on the fact that, if the Ginzburg-Landau parameter kappa does not depend on temperature, the magnetic susceptibility is a universal function of H/H_c2(T), leading to a simple relation between magnetizations at different temperatures. Although this scaling procedure does not provide absolute values of the upper critical fieldH_c2(T), its temperature variation can be established rather accurately. This provides an opportunity to validate theoretical models that are usually employed for the evaluation of H_c2(T) from equilibrium magnetization data. In the second part of the paper we apply this scaling procedure for a discussion of the notorious first order phase transition in the mixed state of high temperature superconductors. Our analysis, based on experimental magnetization data available in the literature, shows that the shift of the magnetization accross the transition may adopt either sign, depending on the particular chosen sample. We argue that this observation is inconsistent with the interpretation that this transition always represents the melting transition of the vortex lattice.Comment: 18 pages, 12 figure

Experimental evidence for fast cluster formation of chain oxygen vacancies in YBa2Cu3O7-d being at the origin of the fishtail anomaly

We report on three different and complementary measurements, namely magnetisation measurements, positron annihilation spectroscopy and NMR measurements, which give evidence that the formation of oxygen vacancy clusters is on the origin of the fishtail anomaly in YBa2Cu3O7-d. While in the case of YBa2Cu3O7.0 the anomaly is intrinsically absent, it can be suppressed in the optimally doped state where vacancies are present. We therefore conclude that the single vacancies or point defects can not be responsible for this anomaly but that clusters of oxygen vacancies are on its origin.Comment: 10 pages, 4 figures, submitted to PR

Systematics of two-component superconductivity in YBa2Cu3O6.95YBa_{2}Cu_{3}O_{6.95} from microwave measurements of high quality single crystals

Systematic microwave surface impedance measurements of YBCO single crystals grown in $BaZrO_3$ crucibles reveal new properties that are not directly seen in similar measurements of other YBCO samples. Two key observations obtained from complex conductivity are: a new normal conductivity peak at around 80K and additional pairing below 65K. High pressure oxygenation of one of the crystals still yields the same results ruling out any effect of macroscopic segregation of O-deficient regions. A single complex order parameter cannot describe these data, and the results suggest at least two superconducting components. Comparisons with model calculations done for various decoupled two-component scenarios (i.e. s+d, d+d) are presented. Systematics of three single crystals show that the 80K quasiparticle peak is correlated with the normal state inelastic scattering rate. Close to Tc, the data follow a mean-field behavior. Overall, our results strongly suggest the presence of multiple pairing temperature and energy scales in $YBa_{2}Cu_{3}O_{6.95}$.Comment: 14 pages, 2-column, Revtex, 5 embedded postscript figures, uses graphicx. Postscript version also available at http://sagar.physics.neu.edu/preprints.htm

First Results for the Beam Commissioning of the CERN Multi-Turn Extraction

The Multi-Turn Extraction (MTE), a new type of extraction based on beam trapping inside stable islands in horizontal phase space, has been commissioned during the 2008 run of the CERN Proton Synchrotron. Both singleand multi-bunch beams with a total intensity up to 1.4 1013 protons have been extracted with efficiencies up to 98%. Furthermore, injection tests in the CERN Super Proton Synchrotron were performed, with the beam then accelerated and extracted to produce neutrinos for the CERN Neutrino-to-Gran Sasso experiments. The results of the extensive measurement campaign are presented and discussed in detail

Direct Observation and Anisotropy of the Contribution of Gap nodes in the Low Temperature Specific Heat of YBa_2Cu_3O_7

The specific heat due to line nodes in the superconducting gap of YBa2Cu3O7 has been obscured up to now by magnetic terms of extrinsic origin, even for high quality crystals. We report the specific heat of a new single crystal grown in a non-corrosive BaZrO3 crucible, for which paramagnetic terms are reduced to less than one spin-1/2 center for 20'000 Cu atoms. The contribution of line nodes shows up directly in the difference C(B,T) - C(0,T) at fixed temperatures (T < 5 K) as a function of the magnetic field parallel to the c-axis (B<=14 T). These data illustrate the smooth crossover from C propotional to T^2 at low fields to C propotional to TB^1/2 at high fields, and provide new values for gap parameters which are quantitatively consistent with tunneling spectroscopy and thermal conductivity in the framework of dx^2-y^2 pairing symmetry. Data for B along the nodal and antinodal directions in the ab-plane are also provided. The in-plane anisotropy predicted in the clean limit is not observed.Comment: 29 pages(using Revtex style), 14 postscript figures, submitted to Phys. Rev. B Content of the file changed after replacin

Imaging Transient Blood Vessel Fusion Events in Zebrafish by Correlative Volume Electron Microscopy

The study of biological processes has become increasingly reliant on obtaining high-resolution spatial and temporal data through imaging techniques. As researchers demand molecular resolution of cellular events in the context of whole organisms, correlation of non-invasive live-organism imaging with electron microscopy in complex three-dimensional samples becomes critical. The developing blood vessels of vertebrates form a highly complex network which cannot be imaged at high resolution using traditional methods. Here we show that the point of fusion between growing blood vessels of transgenic zebrafish, identified in live confocal microscopy, can subsequently be traced through the structure of the organism using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) and Serial Block Face/Scanning Electron Microscopy (SBF/SEM). The resulting data give unprecedented microanatomical detail of the zebrafish and, for the first time, allow visualization of the ultrastructure of a time-limited biological event within the context of a whole organism

Systematic characterization of extracellular vesicle sorting domains and quantification at the single molecule – single vesicle level by fluorescence correlation spectroscopy and single particle imaging

Extracellular vesicles (EV) convey biological information by transmitting macromolecules between cells and tissues and are of great promise as pharmaceutical nanocarriers, and as therapeutic per se. Strategies for customizing the EV surface and cargo are being developed to enable their tracking, visualization, loading with pharmaceutical agents and decoration of the surface with tissue targeting ligands. While much progress has been made in the engineering of EVs, an exhaustive comparative analysis of the most commonly exploited EV-associated proteins, as well as a quantification at the molecular level are lacking. Here, we selected 12 EV-related proteins based on MS-proteomics data for comparative quantification of their EV engineering potential. All proteins were expressed with fluorescent protein (FP) tags in EV-producing cells; both parent cells as well as the recovered vesicles were characterized biochemically and biophysically. Using Fluorescence Correlation Spectroscopy (FCS) we quantified the number of FP-tagged molecules per vesicle. We observed different loading efficiencies and specificities for the different proteins into EVs. For the candidates showing the highest loading efficiency in terms of engineering, the molecular levels in the vesicles did not exceed ca 40–60 fluorescent proteins per vesicle upon transient overexpression in the cells. Some of the GFP-tagged EV reporters showed quenched fluorescence and were either non-vesicular, despite co-purification with EVs, or comprised a significant fraction of truncated GFP. The co-expression of each target protein with CD63 was further quantified by widefield and confocal imaging of single vesicles after double transfection of parent cells. In summary, we provide a quantitative comparison for the most commonly used sorting proteins for bioengineering of EVs and introduce a set of biophysical techniques for straightforward quantitative and qualitative characterization of fluorescent EVs to link single vesicle analysis with single molecule quantification

Observation of d-wave scaling relations in the mixed-state specific heat of YBa2Cu3O7

The low temperature specific heat C(B,T) of an YBa2Cu3O7.00 single crystal is measured from 1.2 to 10 K in magnetic fields up to 14 T. The anisotropic component Caniso(T,B)=C(T,B//c)-C(T,B//ab) is a pure vortex quantity obtained directly from experiment. It follows a scaling relation predicted recently for line nodes characteristic of d-wave vortices. Our experimental field and temperature range corresponds to a crossover region where the limit Caniso(T,B)is proportional to T*sqrt(B) does not strictly apply. The variation of the entropy caused by the magnetic field at low T is thermodynamically compatible with measurements near Tc.Comment: submitted to Phys. Rev. Lett. PDF file, 18 page