MIT Scientists create new form of matter

Seventh State of matter Created by MIT Scientists

Sulekha Rani.R ,PGT Chemistry KV NTPC Kayamkulam

MIT scientists have brought a supercool end to a heated race among physicists: They have become the first to create a new type of matter, a gas of atoms that shows high-temperature superfluidity.

(MIT Professor Wolfgang Ketterle, second from right, poses with three fellow researchers involved in the creation of a new form of matter, a superfluid gas of fermions. From left are Martin Zwierlein, Christian Schunck, Wolfgang Ketterle and Andre Schirotzek.
Photo / Donna Coveney)

Their work, to be reported in the June 23 issue of Nature,is closely related to the superconductivity of electrons in metals. Observations of superfluids may help solve lingering questions about high-temperature superconductivity, which has widespread applications for magnets, sensors and energy-efficient transport of electricity, said Wolfgang Ketterle, a Nobel laureate who heads the MIT group and who is the John D. MacArthur Professor of Physics as well as a principal investigator in MIT's Research Laboratory of Electronics.

Seeing the superfluid gas so clearly is such a dramatic step that Dan Kleppner, director of the MIT-Harvard Center for Ultracold Atoms, said, "This is not a smoking gun for superfluidity. This is a cannon."

For several years, research groups around the world have been studying cold gases of so-called fermionic atoms with the ultimate goal of finding new forms of superfluidity. A superfluid gas can flow without resistance. It can be clearly distinguished from a normal gas when it is rotated. A normal gas rotates like an ordinary object, but a superfluid can only rotate when it forms vortices similar to mini-tornadoes. This gives a rotating superfluid the appearance of Swiss cheese, where the holes are the cores of the mini-tornadoes. "When we saw the first picture of the vortices appear on the computer screen, it was simply breathtaking," said graduate student Martin Zwierlein in recalling the evening of April 13, when the team first saw the superfluid gas. For almost a year, the team had been working on making magnetic fields and laser beams very round so the gas could be set in rotation. "It was like sanding the bumps off of a wheel to make it perfectly round," Zwierlein explained.

(The rotating superfluid gas of fermions is pierced with the vortices, which are like mini-tornadoes.
Image / Andre Schirotzek, MIT)

"In superfluids, as well as in superconductors, particles move in lockstep. They form one big quantum-mechanical wave," explained Ketterle. Such a movement allows superconductors to carry electrical currents without resistance.

The MIT team was able to view these superfluid vortices at extremely cold temperatures, when the fermionic gas was cooled to about 50 billionths of one kelvin, very close to absolute zero (-273 degrees C or -459 degrees F). "It may sound strange to call superfluidity at 50 nanokelvin high-temperature superfluidity, but what matters is the temperature normalized by the density of the particles," Ketterle said. "We have now achieved by far the highest temperature ever." Scaled up to the density of electrons in a metal, the superfluid transition temperature in atomic gases would be higher than room temperature.

Ketterle's team members were MIT graduate students Zwierlein, Andre Schirotzek, and Christian Schunck, all of whom are members of the Center for Ultracold Atoms, as well as former graduate student Jamil Abo-Shaeer.

The team observed fermionic superfluidity in the lithium-6 isotope comprising three protons, three neutrons and three electrons. Since the total number of constituents is odd, lithium-6 is a fermion. Using laser and evaporative cooling techniques, they cooled the gas close to absolute zero. They then trapped the gas in the focus of an infrared laser beam; the electric and magnetic fields of the infrared light held the atoms in place. The last step was to spin a green laser beam around the gas to set it into rotation. A shadow picture of the cloud showed its superfluid behavior: The cloud was pierced by a regular array of vortices, each about the same size.

(In the top portion of this illustration, the gas of fermions (red) is trapped in an infrared laser beam (pink) and held in place by a magnetic field generated by current-carrying coils (blue). Two additional laser beams, shown in green, were used like coffee stirrers to set the gas into rotation. The result, as illustrated below, could be seen in a shadow picture of the expanded cloud that showed its superfluid behavior: The gas was pierced by a regular array of vortices. Image credit: Andre Schirotzek, MIT)

(The rotating superfluid gas of fermions is pierced with the vortices, which are like mini-tornadoes.
Image / Andre Schirotzek, MIT)

The work is based on the MIT group's earlier creation of Bose-Einstein condensates, a form of matter in which particles condense and act as one big wave. Albert Einstein predicted this phenomenon in 1925. Scientists later realized that Bose-Einstein condensation and superfluidity are intimately related.

Bose-Einstein condensation of pairs of fermions that were bound together loosely as molecules was observed in November 2003 by independent teams at the University of Colorado at Boulder, the University of Innsbruck in Austria and at MIT. However, observing Bose-Einstein condensation is not the same as observing superfluidity. Further studies were done by these groups and at the Ecole Normale Superieure in Paris, Duke University and Rice University, but evidence for superfluidity was ambiguous or indirect.

The superfluid Fermi gas created at MIT can also serve as an easily controllable model system to study properties of much denser forms of fermionic matter such as solid superconductors, neutron stars or the quark-gluon plasma that existed in the early universe.

Introduction To Quasicrystals

..Sulekha Rani,R , PGT Chemistry , KV NTPC Kayamkulam

Quasicrystals

In classical crystallography a crystal is defined as a threedimensional periodic arrangement of atoms with translational periodicity along its three principal axes. Thus it is possible to obtain an infinitely extended crystal structure by aligning building blocks called unit-cells until the space is filled up. Normal crystal structures can be described by one of the 230 space groups, which describe the rotational and translational symmetry elements present in the structure. Diffraction patterns of these normal crystals therefore show crystallographic point symmetries (belonging to one of the 11 Laue-groups). In 1984, however, Shechtman, Blech, Gratias & Cahn published a paper which marked the discovery of quasicrystals. They showed electron diffraction patterns of an Al-Mn alloy with sharp reflections and 10-fold symmetry. The whole set of diffraction patterns revealed an icosahedral symmetry of the reciprocal space. Since then many stable and meta-stable quasicrystals were found. These are often binary or ternary intermetallic alloys with aluminium as one of the constituents. The icosahedral quasicrystals form one group and the polygonal quasicrystals another (8,10,12-fold symmetry). We can state that quasicrystals are materials with perfect long-range order, but with no three-dimensional translational periodicity. The former is manifested in the occurrence of sharp diffraction spots and the latter in the presence of a non-crystallographic rotational symmetry.

(Atomic model of an aluminum-palladium-manganese (Al-Pd-Mn) quasicrystal surface.)

quasicrystal, is a structure that is ordered but not periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks translational symmetry. While crystals, according to the classical crystallographic restriction theorem, can possess only two, three, four, and six-fold rotational symmetries, the Bragg diffraction pattern of quasicrystals shows sharp peaks with other symmetry orders, for instance five-fold

Types of Quasicrystals

quasiperiodic in two dimensions (polygonal or dihedral quasicrystals)

There is one periodic direction perpendicular to the quasiperodic layers.

• octagonal quasicrystals with local 8-fold symmetry [primitive & body-centered lattices]
• decagonal quasicrystals with local 10-fold symmetry [primitive lattice]
• dodecagonal quasicrystals with local 12-fold symmetry [primitive lattice]

quasiperiodic in three dimensions, no periodic direction

• icosahedral quasicrystals (axes:12x5-fold, 20x3-fold, 30x2-fold) [primitive, body-centered & face-centered lattices]
• 
  

(A Ho-Mg-Zn icosahedral quasicrystal formed as a dodecahedron, the dual of the icosahedron)

Regarding thermal stability, three types of quasicrystals are distinguished:

§ Stable quasicrystals grown by slow cooling or casting with subsequent annealing,

§ Metastable quasicrystals prepared by melt spinning, and

§ Metastable quasicrystals formed by the crystallization of the amorphous phase.

Except for the Al–Li–Cu system, all the stable quasicrystals are almost free of defects and disorder, as evidenced by x-ray and electron diffraction revealing peak widths as sharp as those of perfect crystals such as Si. Diffraction patterns exhibit fivefold, threefold, and twofold symmetries, and reflections are arranged quasiperiodically in three dimensions.

The origin of the stabilization mechanism is different for the stable and metastable quasicrystals. Nevertheless, there is a common feature observed in most quasicrystal-forming liquid alloys or their undercooled liquids: a local icosahedral order. The icosahedral order is in equilibrium in the liquid state for the stable quasicrystals, whereas the icosahedral order prevails in the undercooled liquid statefor the metastable quasicrystals.

decorative tilings devised by medieval Islamic architects...A Penrose tiling

History...

Before quasicrystals were discovered in 1984 the british mathmatician Roger Penrose devised a way to cover a plane in a nonperiodic fashion using two different types of tiles. An example can be seen on the left. The tiles (rhombii) are arranged in a way that they obey certain matching rules. An equivalent tiling can be obtained for a 3D-arrangement. This is called a 3D-Penrose Tiling, which is made up of rhombohedrons instead of the rhombii. Such 2D and 3D-tilings have several important properties, such as the selfsimilarity, which means that any part of the tiling occurs again within a predictable area (or volume). After the discovery of quasicrystals in 1984 a close resemblance was noted between the icosahedral quasicrystal and the 3D-Penrose pattern. By putting atoms at the vertices of a 3D-Penrose pattern one can obtain a Fourier Transform which explains very well the diffraction patterns of the found Al-Mn quasicrystal. In a similar way one can use 2D-Penrose Tilings (left) to approximate a decagonal quasicrystal, which in a simple case consists of two layers with local 5-fold symmetry, which are rotated by 18 degrees so that the projection along the rotation axis gives a 10-fold symmetry. As stated above it is also possible to derive the vertices of such tilings using the nD-space approach (n>3). In this case we can obtain such a tiling by a projection of a nD periodic lattice (eg. hypercubic lattice).

In short, we can regard quasiperiodic tilings as frameworks that give quasicrystal structures when filled up with atoms in an appropriate way.

Diffreaction Pattern

The symmetry that determines the type of the quasicrystal is first seen in its diffraction pattern. Below some simulations of diffraction patterns are shown, which could represent either electron diffraction patterns or the zeroth layers of precession photographs (X-ray):

Octagonal QC

Decagonal QC

dodecagonal QC

simulation for a Laue pattern (X-ray) from an icosahedral quasicrystal, whereby the x-ray beam is along one of the five-fold axes.

Materials Science of Quasicrystals

Since the original discovery of Dan Shechtman, hundreds of quasicrystals have been reported and confirmed. Undoubtedly, the quasicrystals are no longer a unique form of solid; they exist universally in many metallic alloys and some polymers. Quasicrystals are found most often in aluminium alloys (Al-Li-Cu, Al-Mn-Si, Al-Ni-Co, Al-Pd-Mn, Al-Cu-Fe, Al-Cu-V, etc.), but numerous other compositions are also known (Cd-Yb, Ti-Zr-Ni, Zn-Mg-Ho, Zn-Mg-Sc, In-Ag-Yb, Pd-U-Si, etc.)

Expermental Techniques

selected area electron diffraction (SAED)	obtain reciprocal space information (symmetry, point group)
convergent beam electron diffraction (CBED)	determination of the point group & space group
high resolution transmission electron microscopy (HRTEM)	real structure information (below decagonal Al-Mn-Pd)
X-ray diffraction techniques	Film methods: Laue, Precession, Debye-Sherrer Quantitative measurement: Powder diffractometer, Four-circle diffractometer
neutron diffraction	obtain partial structure factors to assist structure refinement

Structure Solution Techniques

There are basically two different methods for solving the structure of quasicrystals. The first one is a 3D method, where information obtained from HRTEM images and known approximant structures is combined to obtain a realistic structure model.

The second one is the so-called nD structure analysis (n>3), where the structure is modeled in terms of the contents of the nD unit cells, i.e. the occupation domains. In contrast to the 3D method this is a quantitative analysis, which allows to calculate diffraction patterns and to refine a variety of parameters by the least-squares method. It therefore allows us to use all mathematical tools that have been applied in the analysis of conventional crystals, however, extended to the nD space. This technique may include the steps listed below, assuming the application of the nD-maximum entropy method as used by YAMAMOTO et al.

Step 1 - information on the three-dimensional structure
HRTEM images should be taken to obtain as much structural information as possible on the actual three-dimensional structure. For polygonal quasicrystals this means in particular the clarification of the cluster arrangement (in case there are basic clusters that form the whole structure). For icosahedral quasicrystals it is not possible as easily to determine cluster positions, since the high-resolution image shows only the projected structure along some direction. Information on the third spatial coordinate is therefore lost and possibly present clusters cannot accurately be associated with x, y and z-coordinates. The HRTEM images have a limited resolution in direct space so that the actual atom arrangement (distinction between atom species) within one cluster cannot be determined. Therefore an approximant structure can be helpful in giving a possible atom arrangement for some clusters, which can then be introduced into the structure model. An X-ray structure analysis for the approximant is in most cases straightforward and might even have been done before, so that already published data might be readily available.
This step 1 corresponds to the above mentioned first structure solution procedure.

Step 2 - location of occupation domains
The basis for the quasicrystal structure analysis is a single (quasi)crystal X-ray data set, usually taken on a four-circle diffractometer. (In future, however, imaging plate techniques might gain importance, since they allow rapid simultaneous measurements of many reflections including diffuse scattering intensities) The first thing to do with the measured X-ray data is to determine the exact location of the occupation domains. This can be done by using the nD Patterson method, which does not require any structure model, since only the square amplitudes of the structure factors go into the calculation.

Step 3 - nD starting model
The information from the first thwo steps is then combined to obtain a first rough nD structure model. This consists of a number of occupation domains at their determined locations. The occupation domains have to be constructed in such a way that by applying the section method the observed cluster arrangement is obtained, as well as the atomic decoration of the clusters as suggested by a known approximant structure.

Step 4 - MEM (maximum entropy method)
The starting model will then be refined, in order to obtain the phases of some strongest reflections, which is necessary for the MEM calculations. After performing the MEM calculations internal space MEM maps have to be plotted. These MEM maps provide information on the presence of possibly new (additional) occupation domains. Furthermore they show in more detail the size and shape of the occupation domains and the peak heights give hints on the distribution of transition metal atoms.

Step 5 - structure model modification
The information obtained from the MEM maps is then used for the modification of the nD structure model (i.e. the occupation domains). If necessary newly found ODs have to be constructed. The most difficult part is the distribution of atom species among the occupation domains. This is despite the findings in the MEM maps a trial and error procedure, due to the frequently occurring mixed occupancies. Key indicators for a structure model to be reasonable is the calculated point density and the calculated chemical composition.

Step 6 - refinement
The constructed structure model is then refined by means of the least-squares method. The necessity of further model modifications might arise so that steps 5 and 6 have to be repeated until a satisfactory structure solution is found. The refinement should include all necessary positional, occupational and thermal parameters.

Step 7 - structure plots
After obtaining the final structure model, several structure projections need to be drawn in order to elucidate the resulting structure. Since the section method provides all atom positions in x, y and z coordinates, individual clusters can be cut out (using suitable software, such as XRSV) and plotted separately, in order to show more clearly the local structure in the clusters.

System with Quasi Crystals

octagonal QC: V-Ni-Si Cr-Ni-Si Mn-Si Mn-Si-Al Mn-Fe-Si	decagonal QC: Al-TM (TM=Ir,Pd,Pt,Os,Ru,Rh,Mn,Fe,Co,Ni,Cr) Al-Ni-Co * Al-Cu-Mn Al-Cu-Fe Al-Cu-Ni Al-Cu-Co * Al-Cu-Co-Si * Al-Mn-Pd * V-Ni-Si Cr-Ni
dodecagonal QC: Cr-Ni V-Ni V-Ni-Si	icosahedral QC: Al-Mn Al-Mn-Si Al-Li-Cu * Al-Pd-Mn * Al-Cu-Fe Al-Mg-Zn Zn-Mg-RE * (RE=La,Ce,Nd,Sm,Gd,Dy,Y) Ti-TM (TM=Fe, Mn, Co, Ni) Nb-Fe V-Ni-Si Pd-U-Si

* stable phases exist

The Nobel Prize in Chemistry 2011

The Nobel Prize in Chemistry 2011

Sulekha Rani.R , PGT Chemistry, KV NTPC Kayamkulam

The Royal Swedish Academy of Sciences has decided to award the Nobel Prize in Chemistry for 2011 to Dan Shechtman, Technion - Israel Institute of Technology, Haifa, Israel

"for the discovery of quasicrystals".

Dan Shechtman

Born	January 24, 1941 (age 70) Tel Aviv, British Mandate of Palestine
Residence	Israel
Citizenship	Israel
Fields	Materials Science
Institutions	Wright Patterson Air Force Base Johns Hopkins University NIST Iowa State University Technion - Israel Institute of Technology
Alma mater	Technion - Israel Institute of Technology
Known for	Quasicrystals
Notable awards	Wolf Prize in Physics (1998) Israel Prize (1999) Nobel Prize in Chemistry (2011)

(Atomic model of an aluminum-palladium-manganese (Al-Pd-Mn) quasicrystal surface. A silver/aluminium quasicrystal of the type discovered by Nobel prizewinner Daniel Shechtman.)

A remarkable mosaic of atoms

In quasicrystals, we find the fascinating mosaics of the Arabic world reproduced at the level of atoms: regular patterns that never repeat themselves. However, the configuration found in quasicrystals was considered impossible, and Dan Shechtman had to fight a fierce battle against established science. The Nobel Prize in Chemistry 2011 has fundamentally altered how chemists conceive of solid matter.

On the morning of 8 April 1982, an image counter to the laws of nature appeared in Dan Shechtman's electron microscope. In all solid matter, atoms were believed to be packed inside crystals in symmetrical patterns that were repeated periodically over and over again. For scientists, this repetition was required in order to obtain a crystal.

Shechtman's image, however, showed that the atoms in his crystal were packed in a pattern that could not be repeated. Such a pattern was considered just as impossible as creating a football using only six-cornered polygons, when a sphere needs both five- and six-cornered polygons. His discovery was extremely controversial. In the course of defending his findings, he was asked to leave his research group. However, his battle eventually forced scientists to reconsider their conception of the very nature of matter.

Aperiodic mosaics, such as those found in the medieval Islamic mosaics of the Alhambra Palace in Spain and the Darb-i Imam Shrine in Iran, have helped scientists understand what quasicrystals look like at the atomic level. In those mosaics, as in quasicrystals, the patterns are regular - they follow mathematical rules - but they never repeat themselves.

When scientists describe Shechtman's quasicrystals, they use a concept that comes from mathematics and art: the golden ratio. This number had already caught the interest of mathematicians in Ancient Greece, as it often appeared in geometry. In quasicrystals, for instance, the ratio of various distances between atoms is related to the golden mean.

Following Shechtman's discovery, scientists have produced other kinds of quasicrystals in the lab and discovered naturally occurring quasicrystals in mineral samples from a Russian river. A Swedish company has also found quasicrystals in a certain form of steel, where the crystals reinforce the material like armor. Scientists are currently experimenting with using quasicrystals in different products such as frying pans and diesel engines.

(Electron diffraction pattern of an icosahedral Ho-Mg-Zn quasicrystal)

Chemistry of Cooking

Chemistry of Cooking

Sulekha Rani.R , PGT Chemistry, KV NTPC Kayamkulam

"Cooking is chemistry

. "It's essentially chemical reactions."

This kind of chemistry happens when you put chopped red cabbage into a hot pan. Heat breaks down the red anthocyanine pigment, changing it from an acid to alkaline and causing the color change. Add some vinegar to increase the acidity, and the cabbage is red again. Baking soda will change it back to blue.

Cooking vegetables like asparagus causes a different kind of reaction when tiny air cells on the surface hit boiling water.

"If we plunge them into boiling water, we pop these cells, and they suddenly become much brighter green,"

Longer cooking is not so good. It causes the plant's cell walls to shrink and release acid.

"So as it starts gushing out of the cells, and with acid in the water, it turns cooked green vegetables into [a] yucky army drab.

And that pretty fruit bowl on your counter? "Literally, overnight you can go from [a] nice green banana to an overripe banana.

The culprit here is ethylene gas. Given off by apples and even the bananas themselves, it can ruin your perfect fruit bowl -- but put an apple in a paper bag with an unripe avocado, and ethylene gas will work for you overnight.

"We use this as a quick way to ripen

Understanding a little chemistry can help any cook.

Taste and Flavour Facts

Taste and Flavour Facts

Sulekha Rani.R,PGT Chemistry,KV NTPC kayamkulam

Recent scientific research has revealed just how complex our sense of flavour really is. There is no single sense that defines flavour - although we perceive the flavour of food in our mouths, it is our brains that determine flavour. When humans evolved, we had to take whatever food we could - we ate berries and leaves or, when we could kill an animal, raw meat. It was essential to our survival to detect what food was safe, so we honed and evolved our senses to ensure we liked foods that were safe to eat and disliked those that were dangerous.

Our tongues have five different types of sensors (taste buds) - sweet, sour, salt, bitter, and umami (this last has only recently been recognised as a separate taste sensation - the taste of mono sodium glutamate, MSG - found in tomatoes, parmesan cheese and soy sauce, etc.). These are crucial. When we put food in our mouths, we need to decide whether to eat it or spit it out - this can be a life or death decision and needs to be made quickly. We need sugar as a source of energy - so we like sweet tasting foods - if all we taste is sweetness we will eat the food. We need salt to survive - salt has many essential roles - salt affects the electrical conductivity through the body - it governs how our hearts beat, how signals are transmitted along our nerves and in our brains, and controls many other processes.

Glutamic acid is one of the essential amino acids that form the building blocks of proteins - so recognising foods that provide it is important. It therefore not surprising that our "Umami" taste receptors are particularly attuned to the sodium salt of glutamic acid (mono-sodium glumate). Sourness often accompanies foods as they are going off due to bacterial action - think of sour milk - so recognising sourness helps us decide not to eat some foods. Most poisonous berries are taste bitter, so we need to recognise and dislike bitter foods. If we eat a bitter food we will not only spit it out, but follow that up by vomiting to get rid of any trace that may accidentally have got into our digestive systems.

But taste is just the last line of defence - we use all our other senses first - and these affect how we react to different tastes. First we look at the food - is it the "right" colour? Next we touch it - is it firm or soft? At the same time, we listen to how it sounds when we break it - is it crisp or soggy? Then we sniff it - are there any unpleasant odours? All these impressions tell us what to expect when we put food in our mouths. If we are eating berries, we will be looking for sweetness, combined with "fresh" and "tangy" aromas; if it is meat we will be looking for saltiness without any sour "off" aroma. The type of food and our memories of similar foods tell us the key aromas and tastes to look for in the "flavour". All this complex information is processed by our brains and interpreted as the "flavour" and is tasted in our mouths.

Our sense of smell is much more discriminating than our sense of taste. The organ we use to detect aromas is the olfactory bulb, located at the back of our noses near the middle of our heads. Inside the olfactory bulb, we have at least 700 different types of sensor and can use them to distinguish many millions of different molecules. It is not surprising that wine tasters sniff the wines first - their noses are attuned to look for a range of aromas that give clues to the grape variety and region, etc.

But how we use all this information is greatly influenced by the other senses. For example, if you taste a wine you will be influenced by its colour. Indeed, a recent experiment, fooled all the experienced wine tasters. In this experiment, the tasters were asked first to taste six white wines and describe the flavour. They described the flavours using words like "refreshing", "strawberry" and "citrus" to identify different notes in the aroma - these are words frequently used to describe white wines. Then when asked to identify the wines, the tasters were able to correctly identify the grape and the region - some even giving the exact vineyard and vintage.

Next a trick was played - the same six wines were served again, but this time with a little inert red food dye added. This time the tasters used completely different language to describe the flavour - "woody", "tannic" and "powerful" - all words associated with red wines. Then when asked to identify the wines, all plumped for red grape varieties and a few ventured opinions on actual wines they believed they had just tasted. However, when the experiment was repeated again - this time with the tasters blindfolded - they once again got the answers correct.

But there is much more to flavour perception than just the sum of all the different inputs from the eyes, mouth and nose. Our brains, it seems, respond much more to changes in which molecules are in the nose and mouth than they do to what is actually there, for example - if you chew a piece of gum, the flavour will disappear after a few minutes, as your brain gets "bored" by the aroma in the nose - but there is virtually no reduction in the amount of flavour molecules in the nose. However, if you simply change the input from your tongue, by, for example - taking a sip of sweetened water - the full flavour will be instantly restored. The area of flavour perception is one of the most exciting areas for scientific research - it holds out the promise of helping us find ever better ways to produce truly wonderful food.

article ...DCI,... Peter barham....