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We employed a scanning Hall probe microscope to detect the hopping of individual vortices between pinning sites along grain boundaries in YBa2Cu3O6+δ thin films in the presence of an applied current. Detecting the motion of individual vortices allowed us to probe the current-voltage (I-V) characteristics of the grain boundary with voltage sensitivity below a femtovolt. We find a very sharp onset of dissipation with V∝In with an unprecedented high exponent of n≈290 that shows essentially no dependence on temperature or grain boundary angle. Our data have no straightforward explanation within the existing grain boundary transport models. [ABSTRACT FROM AUTHOR]

The authors have fabricated and characterized GaAs/AlxGa1-xAs two-dimensional electron gas scanning Hall probes for imaging perpendicular magnetic fields at surfaces. The Hall crosses range from 85×85 to 1000×1000 nm2. They study low-frequency noise in these probes, especially random telegraph noise, and show that low-frequency noise can be significantly reduced by optimizing the voltage on a gate over the Hall cross. The authors demonstrate a 100 nm Hall probe with a sensitivity of 0.5 G/[Square_Root]Hz (flux sensitivity of 0.25m[uppercase_phi_synonym]0/[Square_Root]Hz; spin sensitivity of 1.2×104μB/[Square_Root]Hz) at 3 Hz and 9 K. [ABSTRACT FROM AUTHOR]

We use scanning superconducting quantum interference device (SQUID) microscopy to investigate the behavior of vortices in the presence of twin boundaries in the pnictide superconductor Ba(Fe1-xCox)2As2. We show that the vortices avoid pinning on twin boundaries. Individual vortices move in a preferential way when manipulated with the SQUID: They tend to not cross a twin boundary, but rather to move parallel to it. This behavior can be explained by the observation of enhanced superfluid density on twin boundaries in Ba(Fe1-xCox)2As2. The observed repulsion from twin boundaries may be a mechanism for enhanced critical currents observed in twinned samples in pnictides and other superconductors. [ABSTRACT FROM AUTHOR]

The extent to which business coalitions and their employer members are catalysts for improving quality of care is of interest to policymakers, who need to know where and under what circumstances the marketplace succeeds on its own in assuring quality. Using data from the 1998 National Business Coalition on Health annual survey, this paper indicates that most coalitions have an infrastructure in place that could be tapped to advance quality goals. Although the survey data cannot tell us the extent to which coalitions are exercising their enhanced market influence specifically to improve quality, interviews with coalition leaders provide insights about how quality considerations can factor into coalition strategies. [ABSTRACT FROM AUTHOR]

A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging. We used a scanning superconducting quantum interference device to show that current in a magnetized topological insulator heterostructure (EuS/Bi2Se3) flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micrometer-scale magnetic structures on the heterostructure and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined by magnetization of the surrounding domain, and its magnitude by the local chemical potential rather than the applied current. Such magnetic structures provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics., (Copyright © 2015, American Association for the Advancement of Science.)

Magnetic flux in superconductors is usually quantized in units of h/2e. Here we report scanning SQUID and scanning Hall probe studies of single fluxoids in high purity YBa2Cu3O6.35 crystals (T(c) less, similar 13 K), extending flux quantization studies to a region of the cuprate phase diagram where the superfluid density is sufficiently low that novel behavior has been predicted. Some scenarios in which superconductivity results from spin-charge separation predict h/e fluxoids in materials with low superfluid density. Our observations of only h/2e fluxoids set limits on these theories.