June 2016: Graphene used as a frequency mixer in new research

A professor, a postdoctoral researcher and a graduate student hop onto a trampoline.

No, it’s not the opening line of a joke. It’s a setup for the explanation of new Cornell-led research involving the wonder material . A group led by Roberto De Alba, graduate student in physics, and Jeevak Parpia, professor and department chair of physics, has published a paper in Nature Nanotechnology regarding yet another application for the versatile, super-strong, super-light material.

Their paper, “Tunable phonon-cavity coupling in graphene membranes,” was published June 13 and describes the ability to use the graphene’s tension as a sort of mediator between vibrational modes, allowing for direct energy transfer from one frequency to another. De Alba was lead author.

Now, back to the trampoline. Let’s establish that the professor jumps at a slow rate, the postdoc at a medium rate and the grad student at a fast rate. They represent the natural modes of the trampoline, which represents the graphene.

If the professor initiates his slow jumping first, followed by the grad student at a much faster rate, the postdoc – by virtue of the jumping that is already going on – is forced into jumping, at his own rate. What’s more, the professor’s jumps become much higher than they were initially, as energy is transferred to him from the faster jumpers. This scenario won’t actually play out in your backyard, but it takes place in graphene because of its high “elastic modulus” – a material property that means any vibrations will cause large changes to the membrane’s tension.

In applying this concept, the group fabricated graphene “drums” with diameters ranging from 5 to 20 micrometers (1 million micrometers = 1 meter). Those drums can be set in motion either by an alternating electric field or by the random thermal vibrations of their constituent atoms (the same atomic vibrations that define an object’s temperature); the movement is detected through laser interferometry, a method devised several years ago at Cornell in Harold Craighead’s group. Craighead is the Charles W. Lake Jr. Professor of Engineering and a collaborator on this work.

External voltage applied to the graphene membrane acts as a sort of “tuning peg” to control the membrane tension and engineer the coupling needed to control one oscillation mode by exciting the other.

“We’ve shown that there is an effect that will convert energy from one mechanical mode to another mechanical mode,” De Alba said. “It allows us to either damp out or amplify vibrations of one mode by activating the other mode.”

“You’re able to change the fundamental frequency of this object’s motion … essentially its thermal motion, by simply applying voltage,” Parpia said.

The term “phonon cavity” was chosen, De Alba said, because the mechanical effect is similar to that of an optical cavity, which can be used to convert energy from laser light into mechanical motion. Phonons are quasi-particles used to describe vibrations in the same way that photons are particles of light.

This discovery paves the way for the application of graphene mechanical resonators in telecommunication applications – for instance, as frequency mixers.

“And because graphene is only a single atom thick, it has such a low mass that it makes a very good force sensor, gas sensor or pressure sensor,” De Alba said. “It could be used in research labs to study ultra-weak forces.”

In addition, when cooled to near absolute zero, these resonators can play a key role in detection of the faintest quantum signals and in identifying and developing new, secure telecommunication technologies.

Read more at: http://phys.org/news/2016-06-graphene-frequency-mixer.html#jCp

 

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June 2016: New high-capability solid-state electron microscope detector enables novel studies of materials

At Cornell University, the Sol M. Gruner (SMG) detector group has developed and demonstrated a new type of imaging electron detector that records an image frame in 1/1000 of a second, and can detect from 1 to 1,000,000 electrons per pixel. This is 1000 times the intensity range, and 100 times the speed of conventional electron microscope image sensors.

Capture of all the transmitted electrons allows quantitative measurement of materials properties, such as internal electric and magnetic fields, which are important for use of the materials in memory and electronics applications.

Cornell University researchers developed and tested a new for electron microscopes that enables quantitative measurements of electric and magnetic fields from micrometers down to atomic resolution. The device is an adaptation of existing solid-state X-ray detector technology, now modified to function as a high-speed, high electron diffraction camera. Dynamic range denotes the maximum range of signals that can be detected by a pixel. The resulting electron microscope pixel array detector records an image frame in under a millisecond, and can detect from 1 to 1,000,000 primary electrons per pixel per image frame. This is 1000 times the dynamic range, and 100 times the speed of conventional electron image sensors. These properties allow us to record the entire unsaturated diffraction pattern in scanning mode, and simultaneously capture bright field, dark field, and phase contrast information, as well as analyze the full scattering distribution, opening the way for new multichannel imaging modes.

Read more at: http://phys.org/news/2016-06-high-capability-solid-state-electron-microscope-detector.html#jCp

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May 2016: Electrical properties of superconductor altered by ‘stretching’

In the early 1970s, in the basement of Clark Hall, the Cornell team of professors David Lee and Robert Richardson, along with then-graduate student Douglas Osheroff, first observed superfluid helium-3. For that breakthrough, the catalyst for further research into low-temperature physics, the trio was awarded the 1996 Nobel Prize in physics.

Twenty years later, another Cornell-led team – working in that same building – has made an important discovery regarding the superconductor strontium ruthenate (Sr2RuO4,or SRO), often described as a crystalline analog of superfluid helium-3. What ties them together is the unusual way the electrons are paired together in SRO, and how the helium atoms are paired in the superfluid. That quality makes SRO intriguing for possible applications in quantum computation.

A team led by Kyle Shen, associate professor of physics, and Darrell Schlom, the Herbert Fisk Johnson Professor of Industrial Chemistry, both members of the Kavli Institute for Nanoscale Science at Cornell, has shown the ability to alter the electrical properties of the unique material through the application of strain – stretching thin films of SRO on top of a single-crystal substrate.

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May 2016: A Pioneer of Scientific Tools Sol Gruner, known for developing x-ray detectors, is a toolmaker, tackling scientific problems and exploring the unknown

by Jackie Swift

“Most scientists focus on a very specific area, but I do many different things,” says Sol Gruner, Physics. “I’m a research mutt. Mainly, I develop tools to attack scientific problems people haven’t looked at yet, largely because the tools needed to solve those problems haven’t existed.”

Gruner’s tool-making expertise has resulted in an array of scientific breakthroughs and developments over the years. One area of research he is well-known for involves the development of new kinds of x-ray detectors for use at synchrotron facilities. X-ray detectors are crucial tools that use x-ray fraction to examine how materials change during experiments, and for several decades, Gruner’s has been one of the foremost groups working in this field. Sol Gruner, known for developing x-ray detectors, is a toolmaker for tackling scientific problems and exploring the unknown.

The Gruner group developed the first pixel array detectors (PADs)—which directly capture x-rays and process the resultant signals in integrated circuit chips—for use in very fast, time-resolved synchrotron science experiments, both at storage ring sources, such as the Cornell High Energy Synchrotron Sources (CHESS), and at x-ray free electron lasers. For example, his group designed the detectors in use at the Linac Coherent Light Source, the world’s first high-energy x-ray free electron laser now operating near Stanford University in California. They allow researchers to look at matter in time scales of femtoseconds (one millionth of one billionth of a second).

– See more at: https://research.cornell.edu/news-features/pioneer-scientific-tools#sthash.tb7udSmM.dpuf

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May 2016: Physicists abuzz about possible new particle as CERN revs up

GENEVA (AP) — Was it a blip, or a breakthrough?

Scientists around the globe are revved up with excitement as the world’s biggest atom smasher – best known for revealing the Higgs boson four years ago – starts whirring again to churn out data that may confirm cautious hints of an entirely new particle.

Such a discovery would all but upend the most basic understanding of physics, experts say.

The European Center for Nuclear Research, or CERN by its French-language acronym, has in recent months given more oomph to the machinery in a 27-kilometer (17-mile) underground circuit along the French-Swiss border known as the Large Hadron Collider.

In a surprise development in December, two separate LHC detectors each turned up faint signs that could indicate a new particle, and since then theorizing has been rife.

“It’s a hint at a possible discovery,” said theoretical physicist Csaba Csaki, who isn’t involved in the experiments. “If this is really true, then it would possibly be the most exciting thing that I have seen in particle physics in my career – more exciting than the discovery of the Higgs itself.”

After a wintertime break, the Large Hadron Collider, or LHC, reopened on March 25 to prepare for a restart in early May. CERN scientists are doing safety tests and scrubbing clean the pipes before slamming together large bundles of particles in hopes of producing enough data to clear up that mystery. Firm answers aren’t expected for weeks, if not until an August conference of physicists in Chicago known as ICHEP.

On Friday, the LHC was temporarily immobilized by a weasel, which invaded a transformer that helps power the machine and set off an electrical outage. CERN says it was one of a few small glitches that will delay by a few days plans to start the data collection at the $4.4 billion collider.

The 2012 confirmation of the Higgs boson, dubbed the “God particle” by some laypeople, culminated a theory first floated decades earlier. The “Higgs” rounded out the Standard Model of physics, which aims to explain how the universe is structured at the infinitesimal level.

The LHC’s Atlas and Compact Muon Solenoid particle detectors in December turned up preliminary readings that suggested a particle not accounted for by the Standard Model might exist at 750 Giga electron Volts. This mystery particle would be nearly four times more massive than the top quark, the most massive particle in the model, and six times more massive than the Higgs, CERN officials say.

The Standard Model has worked well, but has gaps notably about dark matter, which is believed to make up one-quarter of the mass of the universe. Theorists say the December results, if confirmed, could help elucidate that enigma; or it could signal a graviton – a theorized first particle with gravity – or another boson, even hint of a new dimension.

More data is needed to iron those possibilities out, and even then, the December results could just be a blip. But with so much still unexplained, physicists say discoveries of new particles – whether this year or later – may be inevitable as colliders get more and more powerful.

Dave Charlton, who heads the Atlas team, said the December results could just be a “fluctuation” and “in that case, really for science, there’s not really any consequence … At this point, you won’t find any experimentalist who will put any weight on this: We are all very largely expecting it to go away again.”

“But if it stays around, it’s almost a new ball game,” said Charlton, an experimental physicist at the University of Birmingham in Britain.

The unprecedented power of the LHC has turned physics on its head in recent years. Whereas theorists once predicted behaviors that experimentalists would test in the lab, the vast energy being pumped into CERN’s collider means scientists are now seeing results for which there isn’t yet a theoretical explanation.

“This particle – if it’s real – it would be something totally unexpected that tells us we’re missing something interesting,” he said.

Whatever happens, experimentalists and theorists agree that 2016 promises to be exciting because of the sheer amount of data pumped out from the high-intensity collisions at record-high energy of 13 Tera electron Volts, a level first reached on a smaller scale last year, and up from 8 TeVs previously. (CERN likens 1 TeV to the energy generated by a flying mosquito: That may not sound like much, but it’s being generated at a scale a trillion times smaller.)

In energy, the LHC will be nearly at full throttle – its maximum is 14 TeV – and over 2,700 bunches of particles will be in beams that collide at the speed of light, which is “nearly the maximum,” CERN spokesman Arnaud Marsollier said. He said the aim is to produce six times more collisions this year than in 2015.

“When you open up the energies, you open up possibilities to find new particles,” he said. “The window that we’re opening at 13 TeV is very significant. If something exists between 8 and 13 TeV, we’re going to find it.”

Still, both branches of physics are trying to stay skeptical despite the buzz that’s been growing since December.

Csaki, a theorist at Cornell University in Ithaca, New York, stressed that the preliminary results don’t qualify as a discovery yet and there’s a good chance they may turn out not to be true. The Higgs boson had been predicted by physicists for a long time before it was finally confirmed, he noted.

“Right now it’s a statistical game, but the good thing is that there will be a lot of new data coming in this year and hopefully by this summer we will know if this is real or not,” Csaki said, alluding to the Chicago conference. “No vacation in August.”


 

 

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May 2016: Stoltzfus, Thom-Levy to share vice provost for undergrad ed post

Professor Rebecca Stoltzfus has been appointed vice provost for undergraduate education for a five-year term effective July 1, Provost Michael Kotlikoff announced May 9. She will oversee initiatives enhancing undergraduate instruction and related programs, in collaboration with academic leaders and units across campus.

Along with Stoltzfus’ appointment, faculty member Julia Thom-Levy has been named to a new position, the provost’s fellow for pedagogical innovation, for a three-year term beginning Aug. 1. Thom-Levy will focus on curriculum and supporting excellence and innovation in teaching, and will work in close collaboration with Stoltzfus as vice provost. Both positions will report to the provost.

“In seeking to advance our pedagogical mission, we are fortunate to be able to draw on the expertise of both Rebecca and Julia,” Kotlikoff said. “Together they will be invaluable assets in creating and supporting initiatives to enhance learning experiences for all Cornell students.”

The vice provost for undergraduate education works closely and in collaboration with deans and academic associate deans of the university’s undergraduate colleges and schools, as well as with the other vice provosts, the Division of Student and Campus Life, and various units on campus affecting undergraduate life at Cornell.

Responsibilities of the position include direct, and in some cases shared, oversight of initiatives designed to enhance undergraduate instruction and to promote an intellectual community in and out of the classroom and the laboratory, including living and learning experiences in student residences.

Major responsibilities also include accreditation issues related to undergraduate education, support and development of academic initiatives such as undergraduate research, online education, academic integrity, and campus efforts to support inclusivity and academic success for all of Cornell’s students.

“I look forward to promoting the excellence of the Cornell undergraduate experience, and am especially pleased to collaborate with Professor Thom-Levy as a leader in pedagogical innovation,” Stoltzfus said. “It’s a privilege to serve such a creative and diverse community of students and educators.”

Stoltzfus is a professor in the Division of Nutritional Sciences in the College of Human Ecology. She serves as the provost’s fellow for public engagement and directs the Program in Global Health. Her work has included developing partnerships for international student engagement, and she has led in the design of curricular integration of experiential learning.

Her research focuses on causes and consequences of malnutrition among women and children in developing countries, with ongoing projects in Zimbabwe, Zambia, Tanzania and India.

She earned her Cornell doctorate in human nutrition in 1992, taught at Johns Hopkins Bloomberg School of Public Health for a decade and returned to Cornell in 2002 as associate professor of nutritional sciences. She was promoted to professor in 2005.

Thom-Levy, associate professor of physics, came to Cornell in 2005 and has taught introductory physics as well as laboratory and advanced-topics courses in particle physics. She also directs a research group at the Large Hadron Collider at CERN in Geneva, Switzerland, that includes Cornell postdocs and graduate students. She has mentored students in Cornell’s Research Experience for Undergraduates, Hunter R. Rawlings III Presidential Research Scholars and McNair Scholars programs.

She earned her Ph.D. in 2001 at the University of Hamburg, Germany, and has developed instrumentation and operated detectors at the Stanford Linear Accelerator Center, at the Fermi National Accelerator Laboratory near Chicago, and at CERN.

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May 2016: Physicist Katja Nowack Earns DOE Early Career Award

Katja C. Nowack, assistant professor of physics in Cornell’s College of Arts and Sciences, has been selected by the Department of Energy (DOE) to receive $750,000 for research over five years as part of DOE’s Early Career Research Program for her research project, “Magnetic Imaging of Topological Phases of Matter.”

She is one of 49 scientists chosen for the grant, now in its seventh year, which intends to bolster the nation’s scientific workforce by supporting exceptional researchers during their early career years.

Nowack joined the Cornell faculty in January 2015. Her research group is building a set of low-temperature scanning platforms to implement a toolbox of scanning probes that will provide greater understanding of novel quantum materials. Before coming to Cornell, she was a postdoctoral researcher at Stanford University (2011-14) and Delft University of Technology, Netherlands (2010-11), where she received a Ph.D. in physics in 2009.

Said Cherry Murray, director of DOE’s Office of Science: “We invest in promising young researchers early in their careers to support lifelong discovery science to fuel the nation’s innovation system. We are proud of the accomplishments these young scientists already have made, and look forward to following their achievements in years to come.”

Under the program, university-based researchers receive at least $150,000 per year to cover summer salary and research expenses. To be eligible, a researcher must be an untenured, tenure-track assistant or associate professor at a U.S. academic institution or a full-time employee at a DOE national laboratory, who received a Ph.D. within the past 10 years.

Cornell Chronicle

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May 2016: Cornell Astrophysicists Earn Share of $3M Prize

Cornell astrophysicists Saul Teukolsky and Lawrence Kidder have earned a share in the Special Breakthrough Prize in Fundamental Physics – a $3 million award – that recognizes those who helped create the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its ability to find gravitational waves. The discovery announced in February provided strong confirmation of Albert Einstein’s general theory of relativity.

Teukolsky, the Hans A. Bethe Professor of Physics and Astrophysics, and Kidder, senior research associate, played a vital role to validate the historic news of the first direct detection of gravitational waves, predicted a century ago by Einstein.

Theoretical physicist Stephen Hawking, winner of the 2013 Special Breakthrough Prize, noted of the LIGO team, “This discovery has huge significance: firstly, as evidence for general relativity and its predictions of black hole interactions, and secondly as the beginning of a new astronomy that will reveal the universe through a different medium.”

Announcing the award, the prize committee cited Teukolsky and Kidder for their achievement. The Special Breakthrough Prize is given when an extraordinary scientific achievement occurs.

The three founders of LIGO – Ronald W.P. Drever and Kip S. Thorne of the California Institute of Technology and Rainer Weiss of the Massachusetts Institute of Technology – will share $1 million of the award. The remaining $2 million will be shared among 1,012 contributors to the experiment.

Led by scientists from the LIGO collaboration at Caltech and the Virgo group collaboration, research published in February in Physical Review Letters reported detection of gravitational waves resulting from two black holes spiraling in toward one another and smashing together.

Until then, this scenario had only been predicted theoretically. Many astrophysicists doubted it would occur often enough ever to be detected. However, soon after LIGO detectors in Livingston, Louisiana, and Hanford, Washington, were upgraded, in September scientists found two black holes – each about 35 times the mass of our sun – moving at more than half the speed of light, orbiting each other and creating waves. Researchers spent the autumn 2015 confirming results.

LIGO and Virgo researchers confirmed the waves came from a black hole merger by comparing their data with a theoretical model developed at Cornell. Teukolsky and the Cornell-founded Simulation of eXtreme Spacetimes collaboration group have been calculating and completing a full catalog of theoretical solutions since 2000, when supercomputers first became capable of the task.

Founder of the prize Yuri Milner said: “The creative powers of a unique genius, many great scientists, and the universe itself, have come together to make a perfect science story.”

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