Following the people and events that make up the research community at Duke

Students exploring the Innovation Co-Lab

Tag: physics

The Second Kind of Impossible: The Thrilling Discovery of Quasicrystals

Sticky post

The finding of natural quasicrystals is a tale of “crazy stubborn people or stubbornly crazy people,” said physicist and Princeton professor, Paul J. Steinhardt, who spoke at Duke University on October 10 regarding his role in their discovery.

Quasicrystals were once thought to be impossible, as crystals were the only stable form of matter. Crystals allow for periodic patterns of atoms while quasicrystals allow for an ordered, yet non-periodic pattern that results in rotational symmetry. Crystals only allow for two-, three-, four-, and six-fold symmetry and create the geographical shapes of squares/rectangles, triangles, hexagons, and rhombuses (Figure 1). However, quasicrystals allow for ten-fold symmetry with unlimited layers of quasicrystal patterns and various shapes. The penrose tiles (Figure 2) is an example of one-dimensional quasicrystal pattern, while the kitchen tiles of your home is an example of a traditional crystal pattern. 

Figure 1

Figure 2

Steinhardt and his student, Don Levine, published a paper in 1984 attempting to prove the theory of quasicrystals

After the discovery of man-made quasicrystals from a fellow scientist, Steinhardt wanted to find quasicrystals in nature as opposed to laboratories. He began this by contacting museums with global mineral samples in case they contained undiscovered quasicrystals. This did not yield any results. 

Luca Bindi, who then worked for the Museum of Natural History at the University of Florence in Italy, discovered that Steinhardt was searching for natural quasicrystal and wanted to join his endeavors. Bindi found the first interesting sample at the museum he worked in through the rare mineral, khatyrkite, from the Koryak Mountains of Chukotka, Russia. They analyzed the tip of this sample, the width was that of a strand of hair, and discovered the most perfect ten-fold, rotationally symmetric pattern of a quasicrystal from minerals in nature. Even more interesting was that the chemical compound of this quasicrystal, Al63Cu24Fe13, was the exact composition of quasicrystals created in a Japanese laboratory, now found in a rock. 

Steinhardt then took these findings to Lincoln Hollister, a renowned geologist, for his expert opinion. Hollister proceeded to tell Steinhardt that this discovery is impossible as its chemical composition of metallic aluminum cannot be created in nature. Steinhardt wondered if this sample came from a meteorite, which was an “ignorant, stupid suggestion, but Lincoln didn’t know that,” Steinhardt said. Lincoln refers Steinhardt to Glenn Macpherson, an expert meteorologist, who further elaborated that metallic aluminum from meteorites is, once again, impossible. 

Two renowned experts in their fields describing the impossibility of Steinhardt and Bindi’s hypotheses was not enough for them to quit. Their next step was to trace Bindi’s khatyrkite to obtain more samples. Firstly, they attempted to find Nico Koekkoek, a Dutch mineral collector who had sold innumerable mineral samples to various museums. Dead end. Then they wrote to museums globally regarding their khatyrkite samples and discovered four potential samples. All fakes. Yet another dead end. Next was to analyze the legitimate sample in St. Petersburg because any sample of a newly discovered mineral must be given to a museum. The uncooperative discoverer, Leonid Razin, had immigrated to Israel and refused to let anyone touch the sample. They had hit a dead end again.

Bindi relayed this story to his sister and her friend over dinner. The friend’s neighbor shared the same common last name as the Dutch mineral collector, so the friend decided to ask his neighbor if it was an unlikely connection. Miraculously, the neighbor was the widow of the Dutch mineral collector and, after much persuading, handed over her late-husband’s secret diary. The diary reveals a mineral smuggler named Tim from Romania whom he received the khatyrkite. They were unable to locate Tim until Koekkoek’s widow relented yet another secret diary, which revealed that Tim had received these minerals from ‘L. Razin.’ The same Leonid Razin who refused them to view the sample! Eventually, Steinhardt discovered that Leonid Razid had sent a man named Valery Kryachko on an expedition for platinum. While he did not find platinum, he gave his samples to Leonid Razin, which astoundingly contained the natural quasicrystals that Steinhardt had searched for decades. Kryachko was completely unaware of its journey and even provided the remaining sample, which Steinhardt and his team used for testing. 

Steinhardt’s original “ignorant, stupid suggestion” proved remarkably accurate, as they discovered that a meteorite hit Chukotka and resulted in natural metallic aluminum. 

Steinhardt and his dream team needed more samples of khatyrkite to conduct further research. Therefore, seven Russians, five Americans, one Italian, and a cat named Buck set forth the scientific Mission Impossible for natural quasicrystals. They came back with several million grains and after a few weeks, found a sample of clay layer that had not been touched in 10,000 years. This was the first quasicrystal to be declared a natural mineral. They ultimately discovered a total of nine quasicrystal samples, each from a different part of the meteorite. 

Steinhardt and his team’s analysis of quasicrystals is still not over and his book, “The Second Kind of Impossible,” delves further into the outlandish details of the over 30 years of research. This extraordinary journey of passion and ambition allows for the thrilling hope for the future of scientific discovery.

By Samera Eusufzai, Class of 2026

Researchers created a tiny circuit through a single water molecule, and here’s what they found

Graphic by Limin Xiang, Arizona State University

Many university labs may have gone quiet amid coronavirus shutdowns, but faculty continue to analyze data, publish papers and write grants. In this guest post from Duke chemistry professor David Beratan and colleagues, the researchers describe a new study showing how water’s ability to shepherd electrons can change with subtle shifts in a water molecule’s 3-D structure:

Water, the humble combination of hydrogen and oxygen, is essential for life. Despite its central place in nature, relatively little is known about the role that single water molecules play in biology.

Researchers at Duke University, in collaboration with Arizona State University, Pennsylvania State University and University of California-Davis have studied how electrons flow though water molecules, a process crucial for the energy-generating machinery of living systems. The team discovered that the way that water molecules cluster on solid surfaces enables the molecules to be either strong or weak mediators of electron transfer, depending on their orientation. The team’s experiments show that water is able to adopt a higher- or a lower-conducting form, much like the electrical switch on your wall. They were able to shift between the two structures using large electric fields.

In a previous paper published fifteen years ago in the journal Science, Duke chemistry professor David Beratan predicted that water’s mediation properties in living systems would depend on how the water molecules are oriented.

Water assemblies and chains occur throughout biological systems. “If you know the conducting properties of the two forms for a single water molecule, then you can predict the conducting properties of a water chain,” said Limin Xiang, a postdoctoral scholar at University of California, Berkeley, and the first author of the paper.

“Just like the piling up of Lego bricks, you could also pile up a water chain with the two forms of water as the building blocks,” Xiang said.

In addition to discovering the two forms of water, the authors also found that water can change its structure at high voltages. Indeed, when the voltage is large, water switches from a high- to a low-conductive form. In fact, it is may be possible that this switching could gate the flow of electron charge in living systems.

This study marks an important first step in establishing water synthetic structures that could assist in making electrical contact between biomolecules and electrodes. In addition, the research may help reveal nature’s strategies for maintaining appropriate electron transport through water molecules and could shed light on diseases linked to oxidative damage processes.

The researchers dedicate this study to the memory of Prof. Nongjian (NJ) Tao.

CITATION: “Conductance and Configuration of Molecular Gold-Water-Gold Junctions Under Electric Fields,” Limin Xiang, Peng Zhang, Chaoren Liu, Xin He, Haipeng B. Li, Yueqi Li, Zixiao Wang, Joshua Hihath, Seong H. Kim, David N. Beratan and Nongjian Tao. Matter, April 20, 2020. DOI: 10.1016/j.matt.2020.03.023

Guest post by David Beratan and Limin Xiang

Scientists Made a ‘T-Ray’ Laser That Runs on Laughing Gas

‘T-Ray’ laser finally arrives in practical, tunable form. Duke physicist Henry Everitt worked on it over two decades. Courtesy of Chad Scales, US Army Futures Command

It was a Frankenstein moment for Duke alumnus and adjunct physics professor Henry Everitt.

After years of working out the basic principles behind his new laser, last Halloween he was finally ready to put it to the test. He turned some knobs and toggled some switches, and presto, the first bright beam came shooting out.

“It was like, ‘It’s alive!’” Everitt said.

This was no laser for presenting Powerpoint slides or entertaining cats. Everitt and colleagues have invented a new type of laser that emits beams of light in the ‘terahertz gap,’ the no-man’s-land of the electromagnetic spectrum between microwaves and infrared light.

Terahertz radiation, or ‘T-rays,’ can see through clothing and packaging, but without the health hazards of harmful radiation, so they could be used in security scanners to spot concealed weapons without subjecting people to the dangers of X-rays.

It’s also possible to identify substances by the characteristic frequencies they absorb when T-rays hit them, which makes terahertz waves ideal for detecting toxins in the air or gases between the stars. And because such frequencies are higher than those of radio waves and microwaves, they can carry more bandwidth, so terahertz signals could transmit data many times faster than today’s cellular or Wi-Fi networks.

“Imagine a wireless hotspot where you could download a movie to your phone in a fraction of a second,” Everitt said.

Yet despite the potential payoffs, T-rays aren’t widely used because there isn’t a portable, cheap or easy way to make them.

Now Everitt and colleagues at Harvard University and MIT have invented a small, tunable T-ray laser that might help scientists tap into the terahertz band’s potential.

While most terahertz molecular lasers take up an area the size of a ping pong table, the new device could fit in a shoebox. And while previous sources emit light at just one or a few select frequencies, their laser could be tuned to emit over the entire terahertz spectrum, from 0.1 to 10 THz.

The laser’s tunability gives it another practical advantage, researchers say: the ability to adjust how far the T-ray beam travels. Terahertz signals don’t go very far because water vapor in the air absorbs them. But because some terahertz frequencies are more strongly absorbed by the atmosphere than others, the tuning capability of the new laser makes it possible to control how far the waves travel simply by changing the frequency. This might be ideal for applications like keeping car radar sensors from interfering with each other, or restricting wireless signals to short distances so potential eavesdroppers can’t intercept them and listen in.

Everitt and a team co-led by Federico Capasso of Harvard and Steven Johnson of MIT describe their approach this week in the journal Science. The device works by harnessing discrete shifts in the energy levels of spinning gas molecules when they’re hit by another laser emitting infrared light.

Their T-ray laser consists of a pencil-sized copper tube filled with gas, and a 1-millimeter pinhole at one end. A zap from the infrared laser excites the gas molecules within, and when the molecules in this higher energy state outnumber the ones in a lower one, they emit T-rays.

The team dubbed their gizmo the “laughing gas laser” because it uses nitrous oxide, though almost any gas could work, they say.

Duke professor Henry Everitt and MIT graduate student Fan Wang and colleagues have invented a new laser that emits beams of light in the ‘terahertz gap,’ the no-man’s-land of the electromagnetic spectrum.

Everitt started working on terahertz laser designs 35 years ago as a Duke undergraduate in the mid-1980s, when a physics professor named Frank De Lucia offered him a summer job.

De Lucia was interested in improving special lasers called “OPFIR lasers,” which were the most powerful sources of T-rays at the time. They were too bulky for widespread use, and they relied on an equally unwieldy infrared laser called a CO2 laser to excite the gas inside.

Everitt was tasked with trying to generate T-rays with smaller gas laser designs. A summer gig soon grew into an undergraduate honors thesis, and eventually a Ph.D. from Duke, during which he and De Lucia managed to shrink the footprint of their OPFIR lasers from the size of an axe handle to the size of a toothpick.

But the CO2 lasers they were partnered with were still quite cumbersome and dangerous, and each time researchers wanted to produce a different frequency they needed to use a different gas. When more compact and tunable sources of T-rays came to be, OPFIR lasers were largely abandoned.

Everitt would shelf the idea for another decade before a better alternative to the CO2 laser came along, a compact infrared laser invented by Harvard’s Capasso that could be tuned to any frequency over a swath of the infrared spectrum.

By replacing the CO2 laser with Capasso’s laser, Everitt realized they wouldn’t need to change the laser gas anymore to change the frequency. He thought the OPFIR laser approach could make a comeback. So he partnered with Johnson’s team at MIT to work out the theory, then with Capasso’s group to give it a shot.

The team has moved to patent their design, but there is still a long way before it finds its way onto store shelves or into consumers’ hands. Nonetheless, the researchers — who couldn’t resist a laser joke — say the outlook for the technique is “very bright.”

This research was supported by the U.S. Army Research Office (W911NF-19-2-0168, W911NF-13-D-0001) and by the National Science Foundation (ECCS-1614631) and its Materials Research Science and Engineering Center Program (DMR-1419807).

CITATION: “Widely Tunable Compact Terahertz Gas Lasers,” Paul Chevalier, Arman Armizhan, Fan Wang, Marco Piccardo, Steven G. Johnson, Federico Capasso, Henry Everitt. Science, Nov. 15, 2019. DOI: 10.1126/science.aay8683.

Powered by WordPress & Theme by Anders Norén