Commensurability effects in superconducting Nb films with quasiperiodic pinning arrays

We study experimentally the critical depinning current I(c) versus applied magnetic field B in Nb thin films which contain 2D arrays of circular antidots placed on the nodes of quasiperiodic (QP) fivefold Penrose lattices. Close to the transition temperature T(c) we observe matching of the vortex lattice with the QP pinning array, confirming essential features in the I(c)(B) patterns as predicted by Misko et al. [Phys. Rev. Lett. 95, 177007 (2005)]. We find a significant enhancement in I(c)(B) for QP pinning arrays in comparison to I(c) in samples with randomly distributed antidots or no antidots.     

Hydrophobic amplification of noncovalent organocatalysis

The effects of hydrogen-bonding organocatalysts and water for the acceleration of epoxide openings with a variety of nucleophiles are additive and lead to excellent yields of the catalyzed reactions in water.     

Geometric doppler effect: spin-split dispersion of thermal radiation

A geometric Doppler effect manifested by a spin-split dispersion relation of thermal radiation is observed. A spin-dependent dispersion splitting was obtained in a structure consisting of a coupled thermal antenna array. The effect is due to a spin-orbit interaction resulting from the dynamics of the surface waves propagating along the structure whose local anisotropy axis is rotated in space. The observation of the spin-symmetry breaking in thermal radiation may be utilized for manipulation of spontaneous or stimulated emission.     

Realization of Metric Spaces as Inverse Limits, and Bilipschitz Embedding in L 1

We give sufficient conditions for a metric space to bilipschitz embed in L ₁. In particular, if X is a length space and there is a Lipschitz map ${u: X \rightarrow \mathbb R}$ such that for every interval ${I \subset \mathbb R}$ , the connected components of u ^?1(I) have diameter ${\leq {\rm const} \cdot {\rm diam}(I)}$ , then X admits a bilipschitz embedding in L ₁. As a corollary, the Laakso examples, (Geom Funct Anal 10(1):111–123, 2000), bilipschitz embed in L ₁, though they do not embed in any any Banach space with the Radon–Nikodym property (e.g. the space ? ₁ of summable sequences). The spaces appearing the statement of the bilipschitz embedding theorem have an alternate characterization as inverse limits of systems of metric graphs satisfying certain additional conditions. This representation, which may be of independent interest, is the initial part of the proof of the bilipschitz embedding theorem. The rest of the proof uses the combinatorial structure of the inverse system of graphs and a diffusion construction, to produce the embedding in L ₁.     

In‐situ Electrochemical X‐ray Diffraction: A Rigorous Method to Navigate within Phase Diagrams Reveals β‐Fe1+xSe as Superconductor for All x

We report the precise postsynthetic control of the composition of β‐Fe_1+xSe by electrochemistry with simultaneous tracking of the associated structural changes via in situ synchrotron X‐ray diffraction. We access the full phase width of 0.01<x<0.04 and identify the superconducting state below 8 K, which in contrast to earlier reports is independent of the composition. However, in a second set of in situ X‐ray diffraction experiments, we demonstrate that β‐Fe_1+xSe forms a new phase in the presence of oxygen above a 100 °C which has the same anti‐PbO type structure but is not superconducting down to 1.8 K. The latter process can be reversed electrochemically to reinstate the superconducting state. These observations exploit the exquisite control afforded by electrochemistry in contrast with classical approaches of chemical synthesis.