Weirdest martensite: Century-old smectic riddle finally solved

Cornell Chronicle story by Tom Fleischman

Using the latest computer game technology, a Cornell-led team of physicists has come up with a “suitably beautiful” explanation to a puzzle that has baffled researchers in the materials and theoretical physics communities for a century.

Physics professor James Sethna has co-authored a paper on the unusual microstructure of smectics – liquid crystals whose molecules are arranged in layers and form ellipses and hyperbolas – and their similarity to martensites, a crystalline structure of steel.

In fact, Sethna and his cohorts have termed smectic liquids “the world’s weirdest martensite.”

The paper is the April 8 Physical Review Letters cover story. Co-authors include postdoctoral physics researcher Danilo Liarte, physics graduate student Matthew Bierbaum, University of Campinas math professor Ricardo Mosna and University of Pennsylvania physics professor Randall Kamien.

Sethna’s group employed the computing power of a graphics processing unit, or GPU – the technology that has led to the advent of amazingly realistic video games – to run hundreds of numerical simulations. They developed a clustering algorithm and proposed a theory of smectic microstructure that merges the laws of association between smectic liquid crystals and martensites.

“This has been this puzzle for many years, and it finally has a suitably beautiful explanation,” Sethna said. “It ties together ideas from special relativity, and ideas from martensites, to explain this whole puzzle.

“It’s aesthetically beautiful,” he added, “there’s a little bit of Euclidean geometry for those people who actually went to geometry class. It’s like, ‘Ellipses and hyperbolas, I remember those.’ And you pour this (smectic) liquid and it forms these things.”

If you fill a glass with a smectic liquid, due to its layering pattern the liquid forms ellipses and hyperbolas. The ellipses are defects – places where the desired ordering breaks down.

In martensite steel, named for German metallurgist Adolf Martens in 1898, its different low-energy crystal orientations mesh together in microscopic layers to give it a hardness factor far superior to pearlitic and other forms of steel.

In 1910, French physicist Georges Friedel studied a fluid that formed ellipses and hyperbolas, and realized that they must be formed by equally spaced layers of molecules.

Sethna suggests, with a wry smile, that maybe the reason Friedel knew enough to be able to identify these ellipses and hyperbolas is that “he was French. And in France, they used to study much more sophisticated math in high school, and everybody in high school learned about the cyclides of Dupin.”

Like concentric, equally spaced spheres can fill space with only a point defect at the center, the cyclides of Dupin can fill space with only ellipses and hyperbolas as defects. Friedel saw these defects, and deduced the structure.

Kamien had recently deduced that the different shapes of ellipses and hyperbolas could be related by the same rules that govern space and time in special relativity. Kamien and Sethna discussed this problem last spring, when Sethna was on sabbatical at Penn.

“He had this long-standing interest in martensites … and I had an interest in these liquid crystals, smectics,” Kamien said, “and after talking for a while, we realized that these were the same thing.”

Kamien said his interest in smectics was, in part, sparked by a paper Sethna co-wrote with French physicist Maurice Kleman in 1982, “Spheric domains in smectic liquid crystals.”

The recent breakthrough, inspired by the GPU simulations, was to realize the connection between smectics and martensites.

“For over 100 years, these cool focal conics have been a curiosity – they didn’t fit into our system,” says Sethna. “Now we know that these cool cyclides follow the same rules as the crystals that fit together into martensitic steel.”

This work was supported by grants from the U.S. Department of Energy and the Simons Foundation.

 

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Elusive superconductor state observed

Cornell Chronicle

By Bill Steele

A state of electronic matter first predicted by theorists in 1964 has finally been discovered by Cornell physicists and may provide key insights into the workings of high-temperature superconductors.

The prediction was that “Cooper pairs” of electrons in a superconductor could exist in two possible states. They could form a “superfluid” where all the particles are in the same quantum state and all move as a single entity, carrying current with zero resistance – what we usually call a superconductor. Or the Cooper pairs could periodically vary in density across space, a so-called “Cooper pair density wave.” For decades, this novel state has been elusive, possibly because no instrument capable of observing it existed.

Now a research team led by J.C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences, and Andrew P. Mackenzie, director of the Max-Planck Institute CPMS in Dresden, Germany, has developed a new way to use a scanning tunneling microscope (STM) to image Cooper pairs directly.

The work was carried out by Davis Group members Mohammed Hamidian (now at Harvard) and Stephen Edkins (a graduate student at St. Andrews University in Scotland), and is published in the April 13 online edition of the journal Nature.

Superconductivity was first discovered in metals cooled almost to absolute zero (-273.15 degrees Celsius or -459.67 Fahrenheit). Recently developed materials called cuprates – copper oxides laced with other atoms – superconduct at temperatures as “high” as 148 degrees above absolute zero (-125 Celsius). In superconductors electrons join in pairs that are magnetically neutral so they do not interact with atoms and can move without resistance.

Hamidian and Edkins studied a cuprate incorporating bismuth, strontium and calcium (Bi2Sr2CaCu2O8) using an incredibly sensitive STM that scans a surface with sub-nanometer resolution, on a sample that is refrigerated to within a few thousandths of a degree above absolute zero.

At these temperatures Cooper pairs can hop across short distances from one superconductor to another, a phenomenon known as Josephson tunneling. To observe Cooper pairs, the researchers briefly lowered the tip of the probe to touch the surface and pick up a flake of the cuprate material. Cooper pairs could then tunnel between the superconductor surface and the superconducting tip. The instrument became, Davis said, “the world’s first scanning Josephson tunneling microscope.”

Tunneling Cooper pairs create a current flow between the sample and the tip that reveals the density of Cooper pairs at any point, and this showed periodic variations across the sample, with a wavelength of four crystal unit cells. The team had found a Cooper pair density wave state in a high-temperature superconductor, confirming the 50-year-old prediction.

A collateral finding was that Cooper pairs were not seen in the vicinity of a few zinc atoms that had been introduced as impurities, making the overall map of Cooper pairs into “Swiss cheese.”

Density waves may help to explain the so-called “pseudogap” where some materials show symptoms of being superconductors but don’t actually superconduct. Since the pseudogap often appears at relatively high temperatures, understanding it could lead to higher-temperature superconductors that would revolutionize electric power generation and transport.

The researchers noted that their technique could be used to study other cuprates as well as recently discovered iron-based superconductors.

The work was primarily supported by the U.S. Department of Energy Office of Science and a grant to Davis from the EPiQS Program of the Gordon and Betty Moore Foundation.

The collaboration included scientists in Scotland, Germany, Japan and Korea.

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Renowned physicist to examine nature’s moral code

Cornell Chronicle

The ideas of physicist Nima Arkani-Hamed have revolutionized the field of particle theory over the last decade. On April 21, he will turn his attention to “The Morality of Fundamental Physics” in a public lecture as an A.D. White Professor-at-Large.

The talk, at 7 p.m. in Cornell’s Schwartz Auditorium, Rockefeller Hall, is free and open to the public.

The search for nature’s fundamental laws has been associated with “morally correct” explanations and understanding, says Arkani-Hamed.

“This ‘intellectual moral code’ derives its authority from nature, reflecting a deep and still-mysterious unity in our growing understanding of the world of physical and mathematical truth. It also has striking similarities to what we widely recognize as morally good behavior more generally, providing an invariant basis for morality independent of gods or human constructs and conventions.”

His talk will illustrate this notion, using concrete examples ranging from planetary orbits to the structure of quantum field theory.

“Professor Arkani-Hamed is arguably the most brilliant theoretical physicist active today. His insights into the nature of physical laws, the structure of space-time, and the origin and history of the universe are both profound and unconventional,” says Maxim Perelstein, professor of physics. “Every time I hear him speak, I learn something remarkable.”

Yuval Grossman, professor of physics adds , “Not only are Nima’s ideas shaping the landscape of theoretical research, he also does an outstanding job of delivering those ideas to the general public.”

Arkani-Hamed is professor of natural sciences at the Institute for Advanced Study in Princeton, New Jersey. His research focuses on the relationship between theory and experiment. His groundbreaking theories relate to new extra space-time dimensions, super-symmetric extensions of the standard model, the nature of electroweak symmetry breaking and mass generation, the cosmological expansion of the universe, and the nature of dark matter in the universe and, recently, an entirely new idea about the origin of quantum mechanics.

Among his many awards, Arkani-Hamed was an inaugural winner of the $3 million Fundamental Physics Prize, the creation of physicist and internet entrepreneur Yuri Milner. He has also received a Gribov Prize from the European Physical Society and Israel’s Raymond and Beverly Sackler Prize. He was elected to the American Academy of Arts and Sciences in 2009. He received his Ph.D. in physics from the University of California, Berkeley in 1997.

On April 18, Arkani-Hamed will offer a Physics Colloquium talk, “The Future of Collider Physics, on the Earth and in the Sky,” at 4 p.m. in Rockefeller Hall, Schwartz Auditorium.

Arkani-Hamed’s talks are sponsored by the Department of Physics and the A.D. White Professors-at-Large Program.

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Three faculty win Simons Awards

By: Anna Carmichael
March 25, 2016

Three Cornell faculty have been awarded Simons Fellowships in Theoretical Physics for their research. Eun-Ah Kim, associate professor of physics, Dong Lai, professor of astronomy and Maxim Perelstein, professor of physics were honored with the 2016 award from the foundation, which supports scientific research related to mathematics and physical sciences, life sciences and autism, as well as education and outreach efforts.

Kim specializes in high temperature superconductivity, electronic liquid crystals, complex oxides and topological phases. She received her B.S. and M.S. from Seoul National University and her Ph.D. from University of Illinois at Urbana-Champaign. Her post-doc work was done at Stanford University and she has been teaching at Cornell University since 2014.

Lai specializes in theoretical astrophysics. His research projects include astrophysics of compact objects, exoplanets and astrophysical fluid dynamics. He received his undergraduate degrees from the University of Science and Technology of China, his Ph.D. from Cornell in 1994, did postdoctoral work at Caltech and then joined Cornell’s astronomy faculty in 1997.

Perelstein’s current research focuses on finding the mechanism responsible for breaking electroweak symmetry. He also does research in the areas of theoretical cosmology, including theoretical models for dark energy, dark matter and inflation. He received his B.S. from the Moscow Institute for Physics and Technology, his M.S. from the University of California at Los Angeles and his Ph.D. from Stanford University.

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Séamus Davis awarded St. Patrick’s Day Science Medal

Cornell Chronicle article by Linda B. Glaser

Science Foundation Ireland presented its prestigious St. Patrick’s Day Science Medal March 16 to Séamus Davis, Cornell’s James Gilbert White Distinguished Professor in the Physical Sciences. The presentation was made by Charles Flanagan, Ireland’s minister for foreign affairs and trade, as part of St. Patricks’ Day celebrations in Washington, D.C.

This is a wonderful honor, not only for me but for all the scientists at institutions worldwide that form our collaborative research network,” said Davis at the award ceremony. “This award highlights exciting opportunities now emerging from networking the scientific research communities in Ireland and here in the United States. Both countries benefit from this positive relationship, with cross-Atlantic collaboration now playing a vital role in the success of many of the most advanced scientific projects.

“This science medal is also a testament to the world-leading quality of scientific education in Ireland, and to the deep commitment to promote and enhance Ireland’s educational standards today. I am extremely grateful to Science Foundation Ireland for this medal, and I express my gratitude to my family, especially all those at home in Ireland, and to all my colleagues, past and present.”

The award announcement cited Davis as being at the forefront of modern physics for more than 30 years and his inventive and wide-ranging contributions to the physics of quantum materials. His work focuses on the exploration and visualization of electronic structure and behavior at the atomic level, and the exotic new forms of quantum matter found in these advanced materials.

“The type of spectroscopic imaging scanning tunneling microscope [Davis] developed has since spawned a worldwide revolution in electronic quantum matter studies, and replicas of this instrument have now been built in labs at many of the world’s leading research universities,” noted the award announcement.

Now in its third year, the SFI St. Patrick’s Day Science Medal recognizes extraordinary contributions made by U.S.-based scientists, engineers or technology leaders with Irish connections. Davis is a graduate of University College Cork and has extensive personal and research links with Ireland. He is a frequent visitor and speaker at University College Cork, Tyndall National Institute, Royal Irish Academy and University College Dublin, and has worked with the CRANN Research Institute as an adviser.

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Runway role-play becomes a luminous reality

Cornell Chronicle article by Blaine Friedlander

Think “Game of Thrones” meets “Hunger Games.” For the annual Cornell Fashion Collective show on March 12, warriors, rangers and magicians – models draped in LED lights and electroluminescent tape – will role-play on the runway.

For the Cornell Wearable Tech team, led by fiber science student Eric Beaudette ’16 and Lina Sanchez Botero and Neal Reynolds, doctoral students in the fields of fiber science and physics, respectively, the interactive gaming themed collection – called Duality – roars to runway life, exploring real and virtual identities.

“We are showcasing interactive garments for gaming,” said Beaudette. “We’ll focus heavily on the character selection aspect of gaming, with themes of escapism and assuming a new identity in a virtual environment. Each character has a specific role and purpose.”

In addition to smart clothing bedecked with light and tape, the models get tricked out with smart weapons – like swords, bows and staves – that strobe under spells and attacks waged between the good (blue) and evil (red) characters.

“It is almost like laser tag, but with garments and new weapons,” Beaudette said.

For all eight garments, Botero, Reynolds and Beaudette have fused more than 200 LED lights, electroluminescent tape and panels to bring the clothing to lighted life – unveiling the radiant emotions of the characters on the runway. Using Wi-Fi to connect the models’ clothing to each other, the Fashion Collective audience will see clothes reacting to character emotions – and to the garments of other characters.

One character begins as an innocent daughter, but develops combat skills and a desire to avenge her late parents. Through an interactive runway battle scene, the woman’s identity is shaped from the pain of grief that engulfs her, as seen in her clothing ablaze in color, Beaudette explains.

Helping the Cornell Wearable Tech team model the garments at the Fashion Collective are Olivia Butkowski ’16, Lauren Cagnassola ’15, Jeremy Fidock ’17, Madeleine Galvin ’18, Joel Lawson ’16, Alex Quilty ’15, Emily Roehr ’16, Elana Valastro ’17. The hair and makeup stylist is Natani Notah ‘14.

 

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Bethe Lecture focuses on ice telescope’s discoveries

Cornell Chronicle article by Linda B. Glaser

IceCube, one of the world’s most unusual telescopes, has detected a flux of neutrinos reaching us from the cosmos, with energies more than a million times stronger than? those of the neutrinos produced at accelerator laboratories.

These neutrinos are astronomical messengers from the most violent processes in the universe, including giant black holes gobbling up stars in the heart of quasars and gamma-ray bursts, the biggest explosions since the Big Bang.

Principal Investigator Francis Halzen will discuss the IceCube Neutrino Observatory telescope – with sensors buried in 86 holes over 1.5 miles deep in the Antarctic icecap – and highlight its first scientific results as the 2016 Hans Bethe Lecturer in Physics in a public lecture, “Ice Fishing for Neutrinos.” The talk will be held Wednesday, March 23, at 7:30 p.m. in Schwartz Auditorium, Rockefeller Hall.

“The idea that you have to go to the South Pole and look down with a telescope made of ice in order to see neutrinos that are coming from the northern sky is mind blowing,” says Yuval Grossman, physics professor and event organizer. “These neutrinos let us see the universe in ways that were previously inconceivable. In a way it is like the discovery of x-rays that let us look inside a human body.”

Halzen is the Hilldale and Gregory Breit Professor at the University of Wisconsin, Madison, and director of the Institute for Elementary Particle Physics Research. The author of more than 700 papers, he received his master’s degree and doctorate from the University of Louvain, Belgium.

A fellow of the American Physical Society, Hazler’s honors include the Smithsonian American Ingenuity Award for Physical Sciences in 2014 and the Physics World Breakthrough of the Year Award for making the first observation of cosmic neutrinos in 2013.

As part of the Hans Bethe Lecture series, Halzen will also present the physics colloquium, “IceCube: The Discovery of High-Energy Cosmic Neutrinos?” Monday, March 21, at 4 p.m. in Schwartz Auditorium; and a Laboratory of Atomic and Solid State Physics seminar, “IceCube Neutrinos: From Oscillations to PeV Dark Matter,” Tuesday, March 22, at 4 p.m. in 401 Physical Sciences Building.

The Hans Bethe Lectures, established by the Department of Physics and the College of Arts and Sciences, honor Bethe, Cornell professor of physics from 1936 until his death in 2005. Bethe won the Nobel Prize in physics in 1967 for his description of the nuclear processes that power the sun.

Linda B. Glaser is a writer for the College of Arts and Sciences.

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Alum wins physics prize named for Cornell Nobelists

Cornell Chronicle story by Bill Steele

Mohammad Hamidian, Ph.D. ’11, has been named the 2016 winner of the prestigious Lee-Osheroff-Richardson Prize for his discoveries of new forms of electronic matter at the nanoscale and at extreme low temperatures.

In particular he is cited for advances in the technology of scanning tunneling microscopy (STM) to allow operation at ultra-low temperatures – work done in the lab of J.C. Séamus Davis, the James Gilbert White Distinguished Professor in the Physical Sciences. Hamidian was a doctoral student, and later a postdoctoral researcher, in the Davis lab. He is now a research associate in the J.E. Hoffman lab at at Harvard University.

At Cornell, Hamidian invented techniques that, for the first time, enable an STM to observe the quantum states of electrons in samples refrigerated to millikelvin temperatures (a few thousandths of a degree above absolute zero). This allowed him to search for states of electronic quantum matter that only occur at those extremes. His most recent publication with Davis reported the discovery of a so-called Cooper-Pair Density Wave in a superconductor, an elusive electronic state that researchers have been searching for since 1964 but were never previously able to observe.

The prize, sponsored by Oxford Instruments, a manufacturer of devices to observe and manipulate matter at millikelvin temperatures, is named in honor of Cornell researchers David Lee, Douglas Osheroff and the late Robert C. Richardson, joint recipients of the 1996 Nobel Prize in physics for their discovery of superfluidity in helium-3. The winner receives a cash prize of $8,000 and support to attend the 2016 American Physical Society Meeting in March, where the prize will be awarded.

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