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Category: physics

Adding energy to any material, such as by heating it, almost always makes its structure less orderly. Ice, for example, with its crystalline structure, melts to become liquid water, with no order at all.

But in new experiments by physicists at MIT and elsewhere, the opposite happens: When a pattern called a charge density wave in a certain material is hit with a fast laser pulse, a whole new charge density wave is created—a highly ordered state, instead of the expected disorder. The surprising finding could help to reveal unseen properties in materials of all kinds.

The discovery is being reported today in the journal Nature Physics, in a paper by MIT professors Nuh Gedik and Pablo Jarillo-Herrero, postdoc Anshul Kogar, graduate student Alfred Zong, and 17 others at MIT, Harvard University, SLAC National Accelerator Laboratory, Stanford University, and Argonne National Laboratory.

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Adding energy to any material, such as by heating it, almost always makes its structure less orderly. Ice, for example, with its crystalline structure, melts to become liquid water, with no order at all.

But in new experiments by physicists at MIT and elsewhere, the opposite happens: When a pattern called a charge density wave in a certain material is hit with a fast laser pulse, a whole new charge density wave is created — a highly ordered state, instead of the expected disorder. The surprising finding could help to reveal unseen properties in materials of all kinds.

The discovery is being reported today (November 11, 2019) in the journal Nature Physics, in a paper by MIT professors Nuh Gedik and Pablo Jarillo-Herrero, postdoc Anshul Kogar, graduate student Alfred Zong, and 17 others at MIT, Harvard University, SLAC National Accelerator Laboratory, Stanford University, and Argonne National Laboratory.

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This year marks the 20th anniversary of the first time an optical-frequency comb was used to measure the atomic hydrogen 1S-2S optical transition frequency, which was achieved at the Max-Planck-Institut für Quantenoptik (MPQ) in Garching, Germany. Menlo Systems, which was founded soon afterwards as a spin-off from MPQ, has been commercializing and pioneering the technology ever since.

Today, optical frequency combs (OFCs) are routinely employed in applications as diverse as time and frequency metrology, spectroscopy, telecommunications, and fundamental physics. The German company’s fibre-based systems, and its proprietary “figure 9” laser mode-locking technology, have set the precedent for the most stable, reliable, robust, and compact optical frequency combs available on the market today.

An optical frequency comb exploits laser light that comprises up to 106 equidistant, phase-stable frequencies to measure other unknown frequencies with exquisite precision, and with absolute traceability when compared against a radiofrequency standard. The most common and versatile approach to create an OFC is to stabilize an ultrafast mode-locked laser, in which pulses of light bounce back and forth in an optical cavity. The frequency spectrum of the resulting pulse train is a series of very sharp peaks that are evenly spaced in frequency, like the teeth of a comb.

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Scientists analyzing data from a defunct satellite say we should all consider that our universe might be round, rather than flat. The consequences, they explain in a new paper, could be crisis-inducing.

Current theories of the universe, which describe its age, size, and how it evolves over time, are built around a flat spacetime. A new paper reiterates that data from the final Planck satellite release might be better explained by a round universe than a flat universe. Though not everyone agrees with the paper’s conclusions, the authors write that the consequences of assuming a flat universe when the universe is actually round could be dire.

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The celebrated painter Jackson Pollock created his most iconic works not with a brush, but by pouring paint onto the canvas from above, weaving sinuous filaments of color into abstract masterpieces. A team of researchers analyzing the physics of Pollock’s technique has shown that the artist had a keen understanding of a classic phenomenon in fluid dynamics—whether he was aware of it or not.

In a paper published in the journal PLOS ONE, the researchers show that Pollock’s technique seems to intentionally avoid what’s known as coiling instability—the tendency of a viscous fluid to form curls and coils when poured on a surface.

“Like most painters, Jackson Pollock went through a long process of experimentation in order to perfect his technique,” said Roberto Zenit, a professor in Brown’s School of Engineering and senior author on the paper. “What we were trying to do with this research is figure out what conclusions Pollock reached in order to execute his paintings the way he wanted. Our main finding in this paper was that Pollock’s movements and the properties of his paints were such he avoided this coiling instability.”

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