Temperature dependence of the magnetic penetration depth in YBa2Cu3O6.95

We report precision transverse fieldSR measurements of the internal field distribution in the vortex state of crystalline YBa₂Cu₃O_6.95. A novel low background apparatus was used to study a mosaic sample of three high quality single crystals (T_c=93.3K). The observed frequency spectra in magnetic fields of 5kG and 15 kG applied along the c-axis have the characteristic features expected for a regular vortex lattice with some additional broadening. From a preliminary analysis we find that [(0)/(T)]² has a linear temperature coefficient forT<30 K. Such a term is inconsistent with simple s-wave pairing in the superconducting state. These results support recent microwave measurements of(T) on similar crystals in zero applied field but differ significantly from previousSR reports on sintered powders and crystals with lower T_c.This research was supported by the Natural Sciences and Engineering Research Council of Canada.     

One Sample Tests for the Location of Modes of Nonnormal Data

There are few techniques available for testing if modes take specified values. We show that standard tests of location such as the t-test and the Wilcoxon test, which test for the mean and median respectively, can perform poorly as tests for modes when the data is other than unimodal and symmetric. Carolan and Rayner [1] proposed a score test of location for symmetric nonnormal data. We consider a family of distributions similar to those considered by Carolan and Rayner [1] and propose a test for the mode or modes of data from multimodal or skewed distributions and demonstrate by way of simulations that it is reasonably effective.     

Search for magnetic fields due to anyons in high-T c superconductors

We have searched for anomalous internal magnetic fields in highT _c materials which are predicted to occur in anyon and flux phase models of superconductivity. The magnitude, anisotropy and temperature dependence of the observed fields inc-axis oriented samples of sintered YBa₂CuO₃O₇ and of thick-film Bi₂Sr₂CaCu₂O₈ are consistent with a conventional nuclear dipolar origin. An upper limit of ≲0.08 mT is set for any anomalous magnetic fields along thec-axis atμ ⁺ sites in bulk CuO₂ superconductors.     

A pulsed NMR investigation of F chemical shift anisotropy in single crystals of fluorapatite

Measurement of the ¹⁹F NMR frequency versus orientation in single crystals of fluoropatite Ca₅F(PO₄)₃ about two perpendicular crystal axes has allowed determination of all principal components of the nuclear screening tensor, which was found to be axially symmetric with σ_∥ - σ_⊥ ≈ −84 ppm. An explanation of the negative value for σ_∥ - σ_⊥ is suggested by the bonding arrangement most consistent with the crystal structure.     

Perpendicular-field r.f. surface impedance of indium

This paper reports the analysis of experiments on the r.f. surface impednace of thin slabs of single crystal indium in the presence of a d.c. magnetic field normal to the slab plane. While our experimental results are generally in agreement with thos of Krylov, we diverge on their interpretation. Our analysis is based on a calculated Fermi surface model and on numerical calculations of dispersion relations and the surface impedance. We find for the (001) sample plane a weak Doppler-shifted cyclotron resonance (DSCR) absorption in the propagating helicon regime which provides a sensitive test of the model Fermi surface. For the helicon absorption edges corresponding to relatively strong DSCR absorption, the calculated dispersion and surface impedance results for the edge are compared with experimental results for the (001), (100), (111) and (110) sample planes. For the (001) and (110) planes we also observe oscillations in the DSCR absorption regime which are almost periodic in the applied d.c. field. Our surface impedance calculations indicate that these are not Gantmakher-Kaner oscillations but that they correspond to weak DSCR modes with a circular polarization sense opposite to that of the helicons.     

Highly Selective Optical Detection of Fe3+ Ions in Aqueous Solution Using Label‐Free Silicon Nanocrystals

High brightness amine‐terminated silicon nanocrystals (Si NCs) have been utilized in a simple and rapid assay for the highly selective and sensitive detection of Fe³⁺ via quenching of their strong blue luminescence, without the need for analyte‐specific labeling groups. Sensitive detection of Fe³⁺ is successfully demonstrated, with a linear relationship observed between luminescence quenching and Fe³⁺ concentration from 5 × 10^?6 to 900 × 10^?6m and a limit of detection of 1.3 × 10^?6m . The Si NCs show excellent selectivity toward Fe³⁺ ions, with no quenching of the luminescence signal induced by the presence of Fe²⁺ ions, allowing for solution phase discrimination between the ionic species in different charge states.     

Molecular recognition effects in polyaniline

Polyaniline (PANI) is known to dissolve in strong acids, such as sulphonic acids. PANI, in its electrically conductive form, is generally regarded to be poorly soluble in low-acidic solvents and to be infusible, closely resembling fully aromatic rigid rod polymers. We show that “less” acidic solvents and plasticizers can be found based on phenyl-phenyl interactions in combination with hydrogen bonding. The requirement is that the interactions are strong enough and, importantly, sterically match the complementary moieties of the sulphonic acid doped PANI. Dihydroxybenzenes and bisphenols are examples of such low-acidic compounds. This type of molecular recognition allows solution and melt processibility of PANI doped by generic sulphonic acid, such as methanesulphonic acid or alkylbenzenesulphonic acid. Molecular recognition is also offered as an explanation for the previously observed high solubility of camphorsulphonic acid (CSA) doped PANI in phenols.