The current

I think I have missed some very funny things these days. I would like to pile their links below and I'll come back to them as I get time.
1. Physics, 4:26 (2011), by I.I.Mazin. This is a review on the puzzles and surprised conferred by the iron-based superconductors, which shows quasi-3D structure rather than a 2D one, quite different from their cuprate counter-parts.
2. Physics, 4:25 (2011), by P.Recher et al. This is an analog of spin Hall effect. It reviews a work that shows how a line defect could be utilized to filter valley-featured carriers in graphene.
3. Science, 331: 1579 (2011), by R.-H. He et al. This is a sequel to an earlier article by these authors. They have previously argued that, two gaps of distinct origins should exist in cuprates instead of one. Here they further explore their work and show the opening of the pseudogap might be related to a phase transition.

LambdaDCM or MOND ?

Yesterday I encountered an article [http://physics.aps.org/articles/v4/23] and today I attended a public lecture, both on dark matter, which, if it exists, seems invisible to most of the forces known to us. But it does participate in gravitation and plausibly in weak interaction. Their nature is crying to be unveiled. In the article, the author explains the observed v-R curve in galaxies, which is the most direct motivation for dark matter, using the so-called MOND (Modified Newtonian Dynamics) and the dark matter is subsidiary. On the other hand, Harry Nelson, the today's lecturer, dismisses the MOND as unnecessary complications. He cited the "Bullet Cluster" [http://en.wikipedia.org/wiki/Bullet_Cluster] as evidences. All in all, I feel that, the MOND idea can hardly withstand this. The point is that, a good idea should explain not only the v-R curve but also many other relevant things, such as the "Bullet Cluster". On the other hand, what is dark matter ? This is regarded as one of the biggest questions in today's science.

Physics and Physicists: One Clear Difference Between a "Myth" and "Science"

Physics and Physicists: One Clear Difference Between a "Myth" and "Science"

Twist impacts graphene greatly

It is reported that, inter-layer rotation of a stack of graphene drastically changes the electronic properties. For large rotation, the inter-layer effects disappear.

" Stacks of graphene are expected to possess drastically different electronic properties compared to their single-layer components, as a result of interlayer coupling. Theory dictates that graphene’s massless low-energy excitations should disappear, even for the simple bilayer structure. However, experiments have shown that, paradoxically, the electronic properties of single layers somehow survive in layered structures. Theorists have suggested that a relative rotation of one layer with respect to the one below it—a “twist” in the stacking—might be the resolution of the paradox.

Now, in a paper appearing in Physical Review Letters, Adina Luican and collaborators from Rutgers University and the Massachusetts Institute of Technology, both in the US, and the University of Manchester, UK, provide experimental proof of the influence of twisting on the band structure of bilayer graphene. Using scanning tunneling microscopy and spectroscopy, the researchers find that for twist angles above 20°, the electronic properties of the twisted layers are practically indistinguishable from those of single-layer graphene. Based on their measurements, Luican et al. conclude that at small angles, the massless Dirac fermion picture of graphene breaks down and the electronic spectrum is dominated by a saddle point feature, while at large rotation angles, the intersection point in the spectrum shifts to irrelevant high energies and the familiar Dirac energy dispersion is recovered. – Alexios Klironomos " [http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.126802]

How gels sediment

This experiment studies how gel particles move during the course of sedimentation.

"Depending on the kind of colloidal particles it contains, a gel will sediment in a matter of minutes or days. Understanding how shifts in the positions of the typically submicron sized particles affect the more macroscopic sedimentation process (and vice versa) could be helpful in designing industry-use gels. So far, however, no experiments have provided simultaneous access to these vastly different length scales.

Now, a group of scientists in France and Italy report in Physical Review Letters the use of light scattering to capture both the microscopic and macroscopic pictures of a gel collapsing under its own weight.

Giovanni Brambilla of the Université Montpellier, France, and colleagues filled a tall glass column with about 10 mm of a water-based gel. The sticky, colloidal particles in the gel slowly rearranged as the gel started to sediment, altering the specklelike pattern of laser light that the team scattered through a vertical slice of the gel. Over the course of ten days, Brambilla et al. captured this speckle pattern at various heights along the column and used an algorithm to extract such parameters as the particle relaxation rate, sedimentation velocity and density.

The team finds, at least in the slowly settling gels they studied, that both the microscopic and macroscopic dynamics mimic what is found in glassy polymers. Brambilla et al.’s data should thus provide a solid basis on which to test the theory of gels. – Jessica Thomas " [http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.118302]

Celebrating 100 years of superconductivity

This year marks the 100th anniversary since superconductivity was discovered in Leiden, The Netherlands, by Heike Kamerlingh Onnes and co-workers on 8 April 1911. Yielding no less than seven Nobel Prizes, the study of superconductors remains more active than ever in terms of forming a fundamental understanding of their underlying mechanism, and in seeking new and novel applications that already extend to digital electronics, sensors, medicine and metrology.

In recognition of this centennial year we are pleased to present a collection of superconductivity-themed review articles published in Reports on Progress in Physics over the last 10 years. Reflecting the wide-reaching impact of superconductors across many areas of physics, each article will be free to read until the end of 2011.

Tim Smith
Senior Publisher

A One-Way Wall of Silence

In a previous entry I highlighted this work. Here is another citation of it [http://www.sciencemag.org/content/331/6022/twil.full?sa_campaign=Email/toc/3316022twil]:

The recent development of metamaterials and photonic crystals has provided a route to control the propagation of electromagnetic waves through the engineered structure of a material. Combined with transformation optics, such control is rewriting the expected rules of behavior governing the propagation of electromagnetic waves, and offers myriad possibilities ranging from imaging to communications and stealth applications. Sound is also a wave, and so the manipulation of acoustic waves may be expected to carry over by analogy to their electromagnetic counterparts. Li et al. present a sonic crystal composed of a periodic array of steel rods, the geometry of which was selected to give rise to a band gap, whereby the transmission of sound waves in a specific frequency range is prohibited in one direction but allowed in the opposite direction. The authors also show that by mechanically changing the spacing of the array (by rotating the square steel rods), the diode-like behavior can be switched on and off. A range of applications might be expected to follow, from acoustic isolation and filtering to ultrasound imaging.

Phys. Rev. Lett. 106, 84301 (2011).

What happend at the Fukushima reactor ?

The 9.0 level earthquake took place in Japan and caused damage to the nuclear reactors. Now the media are disseminating and making up all kinds of bells and whistles around a possible disaster like Chernobly catastrophe. And the mass and some activists rise to protest against nuclear plants plan. So, the earnest question is, is the nuclear industry really so unsafe ? Here is an excellent article speaking of this. His view is that, the event in Japan witnessed the success of the modern technology, rather than a failure that is spread so widely in the media.

As a nuclear engineer, it is depressing to read the recent reports on the Fukushima nuclear incident — not because of the incident itself (at this point I strongly believe that we will remember Fukushima as evidence of how safe nuclear power is when done right) — but because the media coverage of the event has been rife with errors so glaring that I have to wonder if anyone in the world of journalism has ever taken a physics class. My favorite: in one article, boric acid was described as a “nutrient absorber” instead of a “neutron absorber.” How many editors signed off on that line without asking, “Why would a nuclear reactor need to absorb nutrients?”

Whether it is confusion of radiation with radioactive material, flailing comparisons to past accidents, or hopeless misuse of terminology, reporting on Fukushima has been a mix of hype and speculation entirely devoid of useful information. Let’s set the record straight: the situation is under control, it is unlikely that the nuclear fuel has melted, the risk to the public is effectively zero, and, depending on whether facts on the ground have been reported correctly, it is possible that the reactors will remain capable of producing power in the future.

Gaming into the life of a scientist

I think this is an interesting game. Most people don't have even a clue about the life of a scientist, who usually hardly gets understanding from the mass (which in my opinion, if of course not relevant). This game gives you a chance to experience the science life, although virtually.

A free online game that simulates health-research projects in a virtual world aims to give players a taste of what it is like to be a scientist. In Power of Research (http://www.powerofresearch.eu), launched on 23 February by Biolution, a life-sciences consultancy in Vienna, players imitate the life of a researcher by choosing an institute and research topic, preparing for experiments, applying for funding, seeking staff, publishing results, attending conferences and collaborating with others. They need to be good at negotiation and time management. As players improve, they can win awards or become an institute leader. The game was developed with a 617,000 (US$849,000) grant from the European Commission (EC), and is based on actual institutes and projects in the EC's research funding programme. [Nature 471:257(2011)]

Study blames plasma flow for quiet sun

Our sun is maintained by converting gravitational energy into electromagnetic energy (e.g., visible and invisible radiations). The temperature is so high that the solar matter exists only in gas of light ions and electrons. These are charged particles. Their motions may take the form of the so-called 'plasma', which has these charges moving in a coherent and collective way, appearing as waves. The dynamics are quite nonlinear and intricate. Associated with such plasma, the electromagnetic fields will also change, and have been well known following a very regular pattern. One way to notice this pattern is by counting the intensity of the so-called sunspots, which are caused by pop-ups of strong magnetic energy flow from interior to the surface, like a cork decorated with flares carrying a huge amount of energy that may partly reach the earth. The latest solar cycle peaked in 2001 and was supposed to end in 2008. However, there is something unusual with this cycle: the sun appears too sluggish, with an extra number of spotless days. Now researchers came up with an explanation, which seems under debate [http://www.wired.com/wiredscience/2011/03/spotless-sun-model/]:

Now, Dibyendu Nandy of the Indian Institute of Science Education and Research and colleagues offer an explanation: A “conveyor belt” of plasma inside the sun ran quickly at first and then slowed down.

Nandy and colleagues at Montana State University and the Harvard-Smithsonian Center for Astrophysics ran a computer simulation of magnetic flow inside the sun for 210 sunspot cycles. They randomly varied the speed of plasma flow around a loop called the meridional circulation, which carries magnetic fields from the sun’s interior to its surface and from the equator to the poles.

Observations suggest that the fastest flow runs around 22 meters per second (49 miles per hour). Nandy’s model looked at speeds between 15 and 30 meters per second (33 to 67 miles per hour).

The model found that a fast flow followed by a slow flow reproduced both the weak magnetic field and the dearth of sunspots observed in the last solar minimum.

....

Unfortunately, observations of the sun’s surface seem to directly contradict the new model.

“We’re in this quandary, this clash between theory and observations,” said NASA astronomer David Hathaway, who analyzed 13 years of data from the Solar and Heliospheric Observatory (SOHO) that tracked the movement of charged material near the surface of the sun.

Hathaway agrees that a fast flow can cause weak magnetic fields and fewer sunspots. But his observations, published March 12, 2010 in Science, suggest that the meridional flow was slow in the first half of the last solar cycle, from about 1996 to 2000. Only after the solar maximum did the flow speed up.

“That’s where there’s a problem,” Hathaway said. “We see one thing, they want the opposite to explain the observations.”

Nandy and colleagues point out that the SOHO observations only see plasma moving at the surface of the sun, not in the deep interior where sunspots are born. The surface flows might not reflect what’s going on underneath, he says.

“In an analogy that you might be able to relate to, one could ask, do ripples on the surface of the sea indicate how ocean currents determine the migration of aquatic animals deeper inside?” Nandy said.

Hathaway argues that changes in the surface should be transmitted to the interior at the speed of sound, and should reach the creation zone in half an hour or less. The disagreement between theory and data means there must be a problem with the models, he says.

Postdocs structured into a new permenent post ?

She thinks so:
" The scientific enterprise is run on what economists call the 'tournament' model, with practitioners pitted against one another in bitter pursuit of a very rare prize. Given that cheap and disposable trainees — PhD students and postdocs — fuel the entire scientific research enterprise, it is not surprising that few inside the system seem interested in change. A system complicit in this sort of exploitation is at best indifferent and at worst cruel. I have no doubt that most lab heads want the best for their many apprentices, but at the system level, the practice continues. Few academics could afford to warn trainees against entering the ring — if they frightened away their labour force, research would grind to a halt.

An alternative career structure within science that professionalizes mature postdocs would be better. Permanent research staff positions could be generated and filled with talented and experienced postdocs who do not want to, or cannot, lead a research team — a job that, after all, requires a different skill set. Every academic lab could employ a few of these staff along with a reduced number of trainees. Although the permanent staff would cost more, there would be fewer needed: a researcher with 10–20 years experience is probably at least twice as efficient as a green trainee. Academic labs could thus become smaller, streamlined and more efficient. The slightly fewer trainees in the pool would work in the knowledge that their career prospects are brighter, and that the system that trains them wants to nurture them, not suck them dry and spit them out. "[http://www.nature.com/news/2011/110302/full/471007a.html?WT.ec_id=NATURE-20110303]

Doubts cast on Supersymmetry

Supersymmetry is thought as a beautiful model by particle physicists. However, "beauty" does not guarantee truth. Recent results from LHC runs it in trouble [http://www.nature.com/news/2011/110302/full/471013a.html?WT.ec_id=NATURE-20110303].

"Wonderful, beautiful and unique" is how Gordon Kane describes supersymmetry theory. Kane, a theoretical physicist at the University of Michigan in Ann Arbor, has spent about 30 years working on supersymmetry, a theory that he and many others believe solves a host of problems with our understanding of the subatomic world.

Yet there is growing anxiety that the theory, however elegant it might be, is wrong. Data from the Large Hadron Collider (LHC), a 27-kilometre proton smasher that straddles the French–Swiss border near Geneva, Switzerland, have shown no sign of the 'super particles' that the theory predicts^1–3. "We're painting supersymmetry into a corner," says Chris Lester, a particle physicist at the University of Cambridge, UK, who works with the LHC's ATLAS detector. Along with the LHC's Compact Muon Solenoid experiment, ATLAS has spent the past year hunting for super particles, and is now set to gather more data when the LHC begins a high-power run in the next few weeks. If the detectors fail to find any super particles by the end of the year, the theory could be in serious trouble.

Israel as a science based country

My impression is that, Israel is a great nation, scientific and religious.

Your readers deserve to see research metrics from the Arab world (Nature 469, 453 and 470, 147; 2011) compared with those of its nearest neighbour, Israel.

You compare the number of publications, researchers per million of population and the percentage of gross domestic product (GDP) expended on research and development (R&D). But all of your graphics omit Israel, even though the GDP graphic includes the European Union and Turkey.

The picture would be different had Israel's metrics been included. Israel published 14,943 papers in 2008 (Science Citation Index). In 2007, there were 7,841 researchers per million population, and civilian expenditure on R&D totalled 4.3% of GDP in 2009 — the highest percentage in the world (Central Bureau of Statistics, State of Israel).

From 1948, Israel and its Arab neighbours started on a roughly equal footing. Israel has achieved much, despite arguably being the poorer nation in terms of traditional measures such as land area, natural resources and freedom from conflict. Its strong investment in human capital, fostered by a free and open society, has produced six decades of spectacular growth. Those achievements stand in contrast to six decades of regrettably slow (and relatively static) progress in the Arab world. Your analysis would have been more accurately portrayed in this context. [http://www.nature.com/nature/journal/v471/n7336/full/471037b.html?WT.ec_id=NATURE-20110303]

Trends: Climate Modelling

Brad Marston [Physics, 4:20(2011)] suggests physicists think about tackling climate problems, e.g., how to model climate. He wrote, "In this article, I discuss specific advances in nonequilibrium statistical physics that have direct applications on efforts to understand and predict the climate. (For an excellent introduction to the general science of climate change, see David Archer’s Global Warming: Understanding the Forecast [3].) But first, let’s look at the sort of question a statistical description of the climate system would be expected to answer."

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.