Scenes from the 2019 APS March Meeting

Physics 12, 28
The coldest chip, particle physics under Mao, cell-sized robots, and more stories from the world’s largest physics meeting.
APS/Ken Cole
Boston skyline in the snow.

This year’s March Meeting of the American Physical Society was held in Boston, and, true to form, the city welcomed the conference with a foot of snow. Still, APS reported a record turnout of more than 12,000 attendees.

As always, the expansive menu of talks featured traditional condensed-matter physics peppered with sessions devoted to climate, science communication, and physics history. Attendees marked the 20-year anniversary of network science, held a champagne toast for the 90th birthday of Reviews of Modern Physics, and gathered for a symposium with the 2018 Nobel laureates. Here are a few of the events, sessions, and press conferences that caught our attention. Find out what other attendees talked about by visiting #apsmarch.

–David Ehrenstein, Jessica Thomas, and David Voss

Intro to green energy physics. The day before the March Meeting began, researchers working in the field of green energy and those interested in moving into the field gathered for a day-long workshop. Dan Reicher of Stanford University in California kicked off the talks by describing the three topics all scientists in the field should be familiar with: technology, policy, and finance. Physicists are often good at the first, he explained, but understanding all three is essential to success.

Faster than a speeding fracture. John Kolinski of the Swiss Federal Institute of Technology in Lausanne (EPFL) announced that he and his colleagues have now captured the fastest videos ever recorded of a crack front. Even at one million frames per second, they captured a million pixels per image—500 times as many as top-of-the-line high-speed cameras. Their image processing software starts with a blurred image of a moving crack. It then generates a sequence of frames by assuming that each pixel makes a one-time transition from a “pre-crack” color to a “post-crack” color. The technique is applicable to other fast phenomena and can work with a smartphone camera.

APS/James Roche
March Meeting attendees learning how to add biographies to Wikipedia.

More Wiki bios for women and minorities. A Wikipedia page is the internet’s way of saying you’re someone, but fewer than 20% of bios cover women. Joining an international effort to change that statistic, APS hosted an “edit-a-thon” to create Wiki pages for women and minority physicists. The event attracted over 50 attendees, who—at last count—wrote 26 new bios and updated 39 pages. Postdoc and diversity activist Jess Wade, of Imperial College London, who kicked off the event, highlighted the need for greater diversity in science, saying we need a mixture of perspectives to “determine the science we do and fund.” Read more about Wikipedia edit-a-thons.

Is twisted graphene also “strange”? In a fanfare announcement last year, an MIT team reported that bilayer graphene superconducts if one creates a tiny rotation between the two layers. “Twisted graphene” shares features with cuprate superconductors, in which the electron pairing mechanism is considered “unconventional.” But it’s unclear whether this tantalizing resemblance is “accidental or something deeper,” said Hryhoriy Polshyn of the University of California, Santa Barbara. To learn more, he and his colleagues measured twisted graphene’s resistivity at high temperatures. Their results are consistent with, but don’t prove, to a conventional pairing mechanism (i.e., lattice vibrations). Meanwhile, the MIT team, which did similar experiments, said their data provide evidence for a “strange metal” phase like that found in cuprates.

Sharon Glotzer of the University of Michigan talking about “entropic” crystals at the Kavli Foundation Special Symposium.

Counterintuitive crystals. Physicists learn early on to connect entropy with disorder. But in her talk at the Kavli Foundation Special Symposium, Sharon Glotzer of the University of Michigan showed that the story is incomplete. Focusing on ordering of hard objects, she highlighted her group’s recent computer simulations that show that a rich variety of crystals can form out of collections of building blocks that interact only by excluded volume (no two objects inhabit the same space). After reviewing some of these structures, Glotzer introduced the concept of an “entropic bond,” analogous to a common chemical bond, to explain the stable structures that form with unexpected complexity.

M. Miskin/Univ. of Pennslyvannia/Cornell Univ.
Cell-sized robots are produced using nanofabrication technology, with a single silicon wafer generating a million bots.

Cell-sized robots. Marc Miskin of the University of Pennsylvania in Philadelphia described tiny robots that he and his colleagues have produced by the millions at less than a penny per bot. The devices, created with semiconductor technology, are less than 100 micrometers across and can walk around underwater, powered by laser light. With improvements in remote operation, Miskin imagines someday injecting the bots into humans to carry out tasks like mapping the brain. “We’re not even close to maxing out any of the capabilities of this machine,” he said.

Mao and a lost physics model. Physics has always been intertwined with philosophy, even the political kind. In one of several historical sessions, Jinyan Liu of the Chinese Academy of Sciences spoke of Mao Zedong’s powerful influence on particle physics in China during the 1950s and 1960s (PDF). Mao believed that matter is infinitely divisible, and he was attracted to physicist Shoichi Sakata’s theory on the substructure of elementary particles. Encouraged by their leader to explore similar ideas, Chinese physicists developed the “straton model”—never in the mainstream—in which protons and neutrons have an onion-like substructure that is itself further divisible.

The coldest chip. Cooling nanoscale devices close to absolute zero allows researchers to study quantum effects such as quantum coherence and topological states. The lowest temperature previously achieved was a few millikelvin. But Nikolai Yurttagül of Delft University in the Netherlands reported that he and his colleagues have now managed to cool a nanometer-sized electronic device down to 420 microkelvin and to keep it below 700 microkelvin for more than three days. The team used both on-chip and off-chip magnetic cooling along with other tricks in order to break the 1 mK “barrier.”

David Ehrenstein is the Focus Editor for Physics, Jessica Thomas is the Editor of Physics, and David Voss is the Editor of APS News.

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