Electrons take on diverse jobs in a compound

It was reported that two species of electrons in the same compound were found carrying superconductivity and anti-ferromagnetism, respectively. These two have different mass, one very light while the other quite heavy. This compound has quasi-3D stacked structure, nearly isomorphic to pnictide superconductors. I feel this is funny and many other rich phenomena might happen. "We found that the ZrCuSiAs-type crystal CeNi0:8Bi2 with a layered structure composed of alternate stacking of ½CeNixBið1Þ þ and Bið2Þ exhibits a superconductive transition at 4 K. The conductivities, magnetic susceptibilities, and heat capacities measurements indicate the presence of two types of carriers with notable different masses, i.e., a light electron responsible for superconductivity and a heavy electron interacting with the Ce 4f electron. This observation suggests that 6p electrons of Bi(2) forming the square net and electrons in CeNixBið1Þ layers primarily correspond to the light and heavy electrons, respectively."[PRL, 106:057002(2011)]

How does sulcus develop ?

Sulci is a deep furrow on the surface of soft materials under pressure. It features a catching curvature that nearly breaks the smoothness. These furrows are often seen, examples including the arms of an infant. An interesting question is, how does a sulci develop when applying a compression ? According to this study, the nonlinear response is held liable, "Now, in a paper appearing in Physical Review Letters, Evan Hohlfeld from Harvard University and Lawrence
Berkeley National Laboratory and L. Mahadevan from Harvard University have proposed that the formation of a sulcus is controlled by a new type of instability dominated by nonlinearities in the elastic energy [7]. Their case is bolstered both by detailed numerics and by experiments.
Moreover, they suggest that similar nonlinear instabilities may be lurking behind the formation of many other singular structures found in materials."[physics, 4:19(2011)]

Dark Matter Particles Remain Dark

Here is a controversy about dark matter particles, whose properties are definitely quite elusive. Most we know about them are just speculative. Bear in mind how a scientific conclusion has to go through scrutinies !

Preformed Cooper pairs become localied in the presence of disorder

Enough disorder leads to localized waves, a celebrated assertion due to Anderson. What will happen to superconducting Cooper pairs if disorder is added ? [http://www.nature.com/nphys/journal/v7/n3/full/nphys1892.html?WT.ec_id=NPHYS-201103]

The most profound effect of disorder on electronic systems is the localization of the electrons transforming an otherwise metallic system into an insulator. If the metal is also a superconductor then, at low temperatures, disorder can induce a pronounced transition from a superconducting into an insulating state. An outstanding question is whether the route to insulating behaviour proceeds through the direct localization of Cooper pairs or, alternatively, by a two-step process in which the Cooper pairing is first destroyed followed by the standard localization of single electrons. Here we address this question by studying the local superconducting gap of a highly disordered amorphous superconductor by means of scanning tunnelling spectroscopy. Our measurements reveal that, in the vicinity of the superconductor–insulator transition, the coherence peaks in the one-particle density of states disappear whereas the superconducting gap remains intact, indicating the presence of localized Cooper pairs. Our results provide the first direct evidence that the superconductor–insulator transition in some homogeneously disordered materials is driven by Cooper-pair localization.

Henry's design was found an error

This interesting study has acquired attention from Nature Physics. The authors reveal an error with Henry's design on display in Princeton University.

In 1831, Henry invented a battery-powered rocking-beam motor that he later described as the first electromagnetic machine. He repeatedly modified the design over his career, but only one version of a motor actually constructed by Henry is known to exist. This version is in a collection of Henry instruments at Princeton University. We found that the Princeton motor cannot have operated in the
form that was displayed as early as 1884. We found evidence in several historical documents and in the instrument itself that the field magnet shown with the motor is a mistake. Instead of a single horizontal bar magnet, the motor was designed to use two elliptical magnets. We presume the error was made by whoever assembled the first public display. We modeled the dynamics of Henry’s vibrating motor and compared our results to the operation of a replica motor. Modeling provides
insight into how the motor is able to vibrate indefinitely even in the presence of energy loss due to friction. © 2011 American Association of Physics Teachers.
DOI: 10.1119/1.3531940

More oscillations in cuprate superconductors

http://www.nature.com/nphys/journal/v7/n3/full/nphys1930.html?WT.ec_id=NPHYS-201103

Since its discovery almost 25 years ago, high-temperature superconductivity has led to a wealth of new theoretical ideas and deepened our understanding of complex condensed-matter systems. At the same time, the study of cuprates has been the driving force for tremendous innovations in the experimental methodology of condensed-matter physics, with methods ranging from photoemission, scanning microscopy, optics and neutron scattering to, in the past few years, quantum oscillations. As reported in Nature Physics¹, measurements by Brad Ramshaw et al. of quantum oscillations in the underdoped high-temperature superconductor YBa₂Cu₃O_6.59 typifies these advances in a number of striking ways. First, the samples studied are the result of two decades of intensive development leading to unique levels of purity that would previously have been unimaginable in such complex oxides. Second, the measurements take place in pulsed magnetic fields that reach both a magnitude of field and a quality of signal-to-noise ratio far beyond what could formerly be achieved. And third, the latest innovation of 'genetic algorithms' allows consistent parameters to be extracted from a large data set of quantum oscillations as a function of field direction and temperature. The authors obtain, among other things, a value of the g-factor of the charge carriers near 2, showing that they are surprisingly like free electrons. This result has profound implications for the nature of the ground state that gives rise to these oscillations.

The orbit of photons around black holes

Black hole distorts the space-time on its periphery drastically. This distortion is manifest in everything moving nearby, including photons. A photon is a spin-1 boson, and its orbit can be computed using geodesic equation. Due to the distortion, a photon shall gain excess angular momentum in the course of orbiting. And the trajectory can be very spiral, as this numerical study exposes [http://www.nature.com/nphys/journal/v7/n3/full/nphys1938.html?WT.ec_id=NPHYS-201103].

A photon emitted near a rotating black hole feels the ground beneath it swirl around. Try to run over a rotating surface, such as the platform of a merry-go-round, and you will not only find yourself fighting the Coriolis force; your body follows the rotation and you stagger and stumble. A photon does not stumble, but rotating spacetime can impart to it an intrinsic form of orbital angular momentum (OAM) distinct from its spin. Like other forms of orbital angular momentum, the photon's OAM is quantized by integer multiples of ħ, not just ±ħ. One can visualize OAM by the wavefronts of this twisted light⁷, which are not planar but rather resemble a cylindrical spiral staircase, centred around the light beam (Fig. 1). The intensity pattern of twisted light transverse to the beam shows a dark spot in the middle — where no one would walk on the staircase — surrounded by concentric circles. The twisting of a pure OAM mode can be seen in interference patterns, which show a fork-like structure of partially broken mirror symmetry.