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  • richardmitnick 3:02 pm on September 11, 2014 Permalink | Reply
    Tags: , , MIT Physics   

    From M.I.T.: “Physicists find a new way to push electrons around” 


    MIT News

    September 11, 2014
    David L. Chandler | MIT News Office

    When moving through a conductive material in an electric field, electrons tend to follow the path of least resistance — which runs in the direction of that field.

    temp

    But now physicists at MIT and the University of Manchester have found an unexpectedly different behavior under very specialized conditions — one that might lead to new types of transistors and electronic circuits that could prove highly energy-efficient.

    They’ve found that when a sheet of graphene — a two-dimensional array of pure carbon — is placed atop another two-dimensional material, electrons instead move sideways, perpendicular to the electric field. This happens even without the influence of a magnetic field — the only other known way of inducing such a sideways flow.

    What’s more, two separate streams of electrons would flow in opposite directions, both crosswise to the field, canceling out each other’s electrical charge to produce a “neutral, chargeless current,” explains Leonid Levitov, an MIT professor of physics and a senior author of a paper describing these findings this week in the journal Science.

    The exact angle of this current relative to the electric field can be precisely controlled, Levitov says. He compares it to a sailboat sailing perpendicular to the wind, its angle of motion controlled by adjusting the position of the sail.

    Levitov and co-author Andre Geim at Manchester say this flow could be altered by applying a minute voltage on the gate, allowing the material to function as a transistor. Currents in these materials, being neutral, might not waste much of their energy as heat, as occurs in conventional semiconductors — potentially making the new materials a more efficient basis for computer chips.

    “It is widely believed that new, unconventional approaches to information processing are key for the future of hardware,” Levitov says. “This belief has been the driving force behind a number of important recent developments, in particular spintronics” — in which the spin of electrons, not their electric charge, carries information.

    The MIT and Manchester researchers have demonstrated a simple transistor based on the new material, Levitov says.

    “It is quite a fascinating effect, and it hits a very soft spot in our understanding of complex, so-called topological materials,” Geim says. “It is very rare to come across a phenomenon that bridges materials science, particle physics, relativity, and topology.”

    In their experiments, Levitov, Geim, and their colleagues overlaid the graphene on a layer of boron nitride — a two-dimensional material that forms a hexagonal lattice structure, as graphene does. Together, the two materials form a superlattice that behaves as a semiconductor.

    This superlattice causes electrons to acquire an unexpected twist — which Levitov describes as “a built-in vorticity” — that changes their direction of motion, much as the spin of a ball can curve its trajectory.

    Electrons in graphene behave like massless relativistic particles. The observed effect, however, has no known analog in particle physics, and extends our understanding of how the universe works, the researchers say.

    Whether or not this effect can be harnessed to reduce the energy used by computer chips remains an open question, Levitov concedes. This is an early finding, and while there is clearly an opportunity to reduce energy loss to heat locally, other parts of such a system may counterbalance those gains. “This is a fascinating question that remains to be resolved,” Levitov says.

    Francisco Guinea, a research professor at Spain’s Instituto de Ciencia de Materiales de Madrid, who was not connected with this research, calls the approach taken by this team “novel and imaginative. … The characterization of these currents in graphene is a very important advance in the understanding of two-dimensional materials.”

    The work has great potential, Guinea adds, because “two-dimensional materials with special topological properties are the basis of new technologies for the manipulation of quantum information.”

    In addition to Levitov and Geim, the research team included Roman Gorbachev, a research fellow at Manchester; Justin Song, a graduate student at MIT who is now at Caltech; Geliang Yu, a graduate student at Manchester; Freddie Withers, Yang Cao, and Artem Mishchenko, who are postdocs at Manchester; and Manchester professors Irina Grigorieva and Konstantin Novoselov. The work was supported by the European Research Council, the Royal Society, the National Science Foundation, the Office of Naval Research, and the Air Force Office of Scientific Research.

    See the full article here.

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  • richardmitnick 7:52 am on October 4, 2013 Permalink | Reply
    Tags: , , , MIT Physics   

    From M.I.T.: “New kind of microscope uses neutrons” 

    October 4, 2013
    David L. Chandler, MIT News Office

    Researchers at MIT, working with partners at NASA, have developed a new concept for a microscope that would use neutrons — subatomic particles with no electrical charge — instead of beams of light or electrons to create high-resolution images.

    micro
    No image credit

    Among other features, neutron-based instruments have the ability to probe inside metal objects — such as fuel cells, batteries, and engines, even when in use — to learn details of their internal structure. Neutron instruments are also uniquely sensitive to magnetic properties and to lighter elements that are important in biological materials.

    The new concept has been outlined in a series of research papers this year, including one published this week in Nature Communications by MIT postdoc Dazhi Liu, research scientist Boris Khaykovich, professor David Moncton, and four others.

    See the full article here.


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  • richardmitnick 2:54 pm on July 25, 2013 Permalink | Reply
    Tags: , , , , MIT Physics, , , , Superfluids   

    From M.I.T.: “Superfluid turbulence through the lens of black holes” 

    Study finds behavior of the turbulent flow of superfluids is opposite that of ordinary fluids.

    July 25, 2013
    Jennifer Chu, MIT News Office

    “A superfluid moves like a completely frictionless liquid, seemingly able to propel itself without any hindrance from gravity or surface tension. The physics underlying these materials — which appear to defy the conventional laws of physics — has fascinated scientists for decades.

    fluid
    Black hole physics shows that superfluids in turbulence behave much like cigarette smoke. Image: Christine Daniloff

    Think of the assassin T-1000 in the movie “Terminator 2: Judgment Day” — a robotic shape-shifter made of liquid metal. Or better yet, consider a real-world example: liquid helium. When cooled to extremely low temperatures, helium exhibits behavior that is otherwise impossible in ordinary fluids. For instance, the superfluid can squeeze through pores as small as a molecule, and climb up and over the walls of a glass. It can even remain in motion years after a centrifuge containing it has stopped spinning.

    Now physicists at MIT have come up with a method to mathematically describe the behavior of superfluids — in particular, the turbulent flows within superfluids. They publish their results this week in the journal Science.

    ‘Turbulence provides a fascinating window into the dynamics of a superfluid,’ says Allan Adams, an associate professor of physics at MIT. ‘Imagine pouring milk into a cup of tea. As soon as the milk hits the tea, it flares out into whirls and eddies, which stretch and split into filigree. Understanding this complicated, roiling turbulent state is one of the great challenges of fluid dynamics. When it comes to superfluids, whose detailed dynamics depend on quantum mechanics, the problem of turbulence is an even tougher nut to crack.’

    To describe the underlying physics of a superfluid’s turbulence, Adams and his colleagues drew comparisons with the physics governing black holes. At first glance, black holes — extremely dense, gravitationally intense objects that pull in surrounding matter and light — may not appear to behave like a fluid. But the MIT researchers translated the physics of black holes to that of superfluid turbulence, using a technique called holographic duality.

    Consider, for example, a holographic image on a magazine cover. The data, or pixels, in the image exist on a flat surface, but can appear three-dimensional when viewed from certain angles. An engineer could conceivably build an actual 3-D replica based on the information, or dimensions, found in the 2-D hologram.

    ‘If you take that analogy one step further, in a certain sense you can regard various quantum theories as being a holographic image of a world with one extra dimension,’ says Paul Chesler, a postdoc in MIT’s Department of Physics.

    Taking this cosmic line of reasoning, Adams, Chesler and colleagues used holographic duality as a ‘dictionary’ to translate the very well-characterized physics of black holes to the physics of superfluid turbulence.

    To the researchers’ surprise, their calculations showed that turbulent flows of a class of superfluids on a flat surface behave not like those of ordinary fluids in 2-D, but more like 3-D fluids, which morph from relatively uniform, large structures to smaller and smaller structures. The result is much like cigarette smoke: From a burning tip, smoke unfurls in a single stream that quickly disperses into smaller and smaller eddies. Physicists refer to this phenomenon as an “energy cascade.”

    ‘For superfluids, whether such energy cascades exist is an open question,’ says Hong Liu, an associate professor of physics at MIT. ‘People have been making all kinds of claims, but there hasn’t been any smoking-gun type of evidence that such a cascade exists. In a class of superfluids, we produced very convincing evidence for the direction of this kind of flow, which would otherwise be very hard to obtain.’”

    See the full article here.


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  • richardmitnick 12:09 pm on January 11, 2013 Permalink | Reply
    Tags: , , , MIT Physics,   

    From M.I.T. : “How to treat heat like light” 

    January 11, 2013
    David L. Chandler

    An MIT researcher has developed a technique that provides a new way of manipulating heat, allowing it to be controlled much as light waves can be manipulated by lenses and mirrors.
    The approach relies on engineered materials consisting of nanostructured semiconductor alloy crystals. Heat is a vibration of matter — technically, a vibration of the atomic lattice of a material — just as sound is. Such vibrations can also be thought of as a stream of phonons — a kind of “virtual particle” that is analogous to the photons that carry light. The new approach is similar to recently developed photonic crystals that can control the passage of light, and phononic crystals that can do the same for sound.

    lattice
    Thermal lattices, shown here, are one possible application of the newly developed thermocrystals. In these structures, where precisely spaced air gaps (dark circles) control the flow of heat, thermal energy can be “pinned” in place by defects introduced into the structure (colored areas).
    Image courtesy of the researchers

    The spacing of tiny gaps in these materials is tuned to match the wavelength of the heat phonons, explains Martin Maldovan, a research scientist in MIT’s Department of Materials Science and Engineering and author of a paper on the new findings published Jan. 11 in the journal Physical Review Letters.”

    See the full article here.


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  • richardmitnick 11:42 am on August 31, 2012 Permalink | Reply
    Tags: , , MIT Physics, , ,   

    From MIT News: “A one-way street for spinning atoms” 

    Work correlating ultracold atoms’ spin with their direction of motion may help physicists model new circuit devices and unusual phases of matter.

    August 30, 2012
    News Office

    Elementary particles have a property called spin that can be thought of as rotation around their axes. In work reported this week in the journal Physical Review Letters, MIT physicists have imposed a stringent set of traffic rules on atomic particles in a gas: Those spinning clockwise can move in only one direction, while those spinning counterclockwise can move only in the other direction.

    image
    Elementary particles have a fundamental property called ‘spin’ that determines how they align in a magnetic field. MIT researchers have created a new physical system in which atoms with clockwise spin move in only one direction, while atoms with counterclockwise spin move in the opposite direction.
    Graphic: Christine Daniloff

    Physical materials with this distinctive property could be used in “spintronic” circuit devices that rely on spin rather than electrical current for transferring information. The correlation between spin and direction of motion is crucial to creating a so-called topological superfluid, a key ingredient of some quantum-computing proposals.

    The MIT team, led by Martin Zwierlein, an associate professor of physics and a principal investigator in the Research Laboratory of Electronics (RLE), produced this spin-velocity correlation in an ultracold, dilute gas of atoms.

    The MIT research was funded in part by the National Science Foundation, the Air Force Office of Scientific Research, the Office of Naval Research, the Army Research Office with funding from the DARPA Optical Lattice Emulator program, and the David and Lucile Packard Foundation.

    See the full and important article here.


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  • richardmitnick 3:41 pm on July 31, 2012 Permalink | Reply
    Tags: , MIT Physics   

    From MIT News: “Alan Guth wins $3 million Fundamental Physics Prize” 

    Alan Guth ’69, SM ’69, PhD ’72, the Victor F. Weisskopf Professor of Physics at MIT, is among nine physicists worldwide selected as inaugural winners of the Fundamental Physics Prize, the Milner Foundation announced today.

    ag

    Congratulations to this graduate of Highland Park High School, Highland Park, NJ, USA, which also educated Eric, Jodi and Josh. What can I say, I could not let this go by.

    This year’s recipients — each of whom will receive $3 million in recognition of past research achievements in physics — will form a selection committee for future winners of the Fundamental Physics Prize. After this year, it is expected that the prize will be awarded to one physicist annually for what the Milner Foundation described in a statement as ‘transformative advances in the field.’”

     
  • richardmitnick 2:54 pm on July 25, 2012 Permalink | Reply
    Tags: , , , MIT Physics, , ,   

    From MIT News: “Single-photon transmitter could enable new quantum devices” 

    July 25, 2012
    David L. Chandler

    Long-sought goal for quantum devices — the ability to transmit single photons while blocking multiple photons — is finally achieved.

    In theory, quantum computers should be able to perform certain kinds of complex calculations much faster than conventional computers, and quantum-based communication could be invulnerable to eavesdropping. But producing quantum components for real-world devices has proved to be fraught with daunting challenges.

    cloud
    An artist’s conception shows how any number of incoming photons (top) can be absorbed by a cloud of ultra-cold atoms (center), tuned so that only one single photon can pass through at a time. Being able to produce a controlled beam of single photons has been a goal of research toward creating quantum devices. Graphic: Christine Daniloff

    Now, a team of researchers at MIT and Harvard University has achieved a crucial long-term goal of such efforts: the ability to convert a laser beam into a stream of single photons, or particles of light, in a controlled way. The successful demonstration of this achievement is detailed in a paper published this week in the journal Nature by MIT doctoral student Thibault Peyronel and colleagues.

    See the full article here.

     
  • richardmitnick 9:32 am on June 5, 2012 Permalink | Reply
    Tags: , , , , MIT Physics,   

    From M.I.T.: “NSE fusion program moves beyond plasma, towards practical power-plant issues” 

    “Nuclear fusion is a seemingly ideal energy source: carbon-free, fuel derived largely from seawater, no risk of runaway reactors and minimal waste issues. And the MIT Department of Nuclear Science and Engineering’s (NSE) long-standing fusion program is extending its leadership role in advancing the technology toward practical use.

    NSE’s Plasma Science and Fusion Center (PFSC), home of one of just three U.S. tokamak fusion reactors, has been a focal point of fusion research since its founding in 1976, developing substantial basic knowledge about creating and maintaining fusion reactions. And today, explains Professor Dennis Whyte, NSE’s fusion team is beginning a strategic pivot into the next stage of development, with a focus on interdisciplinary knowledge needed for the creation of functioning
    powerplants.

    tok
    A tokamak

    ‘We’re basically making energy by creating a star,’ explains Whyte. ‘For power generation, the star has to turn on, and stay on for a year at a time, and we need a way to extract the energy it creates.’”

    See the full article here.

     
  • richardmitnick 3:06 pm on July 6, 2011 Permalink | Reply
    Tags: MIT Physics,   

    From MIT News: “A new way to build nanostructures” 

    Combining top-down and bottom-up approaches, new low-cost method could be a boon to research with a variety of applications.

    David L. Chandler, MIT News Office
    July 6, 2011

    “The making of three-dimensional nanostructured materials — ones that have distinctive shapes and structures at scales of a few billionths of a meter — has become a fertile area of research, producing materials that are useful for electronics, photonics, phononics and biomedical devices. But the methods of making such materials have been limited in the 3-D complexity they can produce. Now, an MIT team has found a way to produce more complicated structures by using a blend of current “top-down” and “bottom-up” approaches.

    The work is described in a paper published in June in the journal Nano Letters, co-authored by postdoc Chih-Hao Chang; George Barbastathis, the Singapore Research Professor of Optics and Professor of Mechanical Engineering; and six MIT graduate students.

    i1
    The new 3D nanofabrication method makes it possible to manufacture complex multi-layered solids all in one step. In this example, seen in these Scanning Electron Microscope images, a view from above (at top) shows alternating layers containing round holes and long bars. As seen from the side (lower image), the alternating shapes repeat through several layers. Image: Chih-Hao Chang

    See the full article here.

     
  • richardmitnick 10:51 am on May 13, 2011 Permalink | Reply
    Tags: , MIT Physics,   

    From MIT News: “Toward faster transistors” 

    MIT physicists discover a new physical phenomenon that could eventually lead to the first increases in computers’ clock speed since 2002.

    Larry Hardesty, MIT News Office

    “In the 1980s and ’90s, competition in the computer industry was all about “clock speed” — how many megahertz, and ultimately gigahertz, a chip could boast. But clock speeds stalled out almost 10 years ago: Chips that run faster also run hotter, and with existing technology, there seems to be no way to increase clock speed without causing chips to overheat.

    In this week’s issue of the journal Science, MIT researchers and their colleagues at the University of Augsburg in Germany report the discovery of a new physical phenomenon that could yield transistors with greatly enhanced capacitance — a measure of the voltage required to move a charge. And that, in turn, could lead to the revival of clock speed as the measure of a computer’s power.”

    i1
    MIT researchers and colleagues at the University of Augsburg, in Germany, investigated the curious electrical properties of a material produced by stacking layers of lanthanum aluminate on layers of strontium titanate.

    i2
    The researchers’ experimental setup consisted of a sample of the lanthanum aluminate-strontium titanate composite, which looks like a slab of thick glass, with thin electrodes deposited on top of it.

    See the full exciting article here.

     
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