{"id":40787,"date":"2023-02-16T01:15:50","date_gmt":"2023-02-16T02:15:50","guid":{"rendered":"https:\/\/peymantaeidi.net\/stem-cell\/?p=40787"},"modified":"2023-02-16T02:37:50","modified_gmt":"2023-02-16T02:37:50","slug":"mit-physicists-discover-way-to-switch-superconductivity-on-and-off-in-magic-angle-graphene","status":"publish","type":"post","link":"https:\/\/peymantaeidi.net\/stem-cell\/2023\/02\/16\/mit-physicists-discover-way-to-switch-superconductivity-on-and-off-in-magic-angle-graphene\/","title":{"rendered":"MIT Physicists Discover Way To Switch Superconductivity On and Off in \u201cMagic-Angle\u201d Graphene"},"content":{"rendered":"
\"Switch<\/p>\n

MIT physicists have found a new way to switch superconductivity on and off in magic-angle graphene. This figure shows a device with two graphene layers in the middle (in dark gray and in inset). The graphene layers are sandwiched in between boron nitride layers (in blue and purple). The angle and alignment of each layer enables the researchers to turn superconductivity on and off in graphene with a short electric pulse. Credit: Courtesy of the researchers. Edited by MIT News<\/p>\n

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Applying a quick electric pulse completely flips the material\u2019s electronic properties, opening a route to ultrafast, brain-inspired, superconducting electronics.<\/strong><\/p>\n

MIT<\/p>\n

MIT is an acronym for the Massachusetts Institute of Technology. It is a prestigious private research university in Cambridge, Massachusetts that was founded in 1861. It is organized into five Schools: architecture and planning; engineering; humanities, arts, and social sciences; management; and science. MIT's impact includes many scientific breakthroughs and technological advances. Their stated goal is to make a better world through education, research, and innovation.<\/div>\n

” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]”>MIT<\/span> physicists have revealed a new and exotic property in \u201cmagic-angle\u201d graphene<\/p>\n

Graphene is an allotrope of carbon in the form of a single layer of atoms in a two-dimensional hexagonal lattice in which one atom forms each vertex. It is the basic structural element of other allotropes of carbon, including graphite, charcoal, carbon nanotubes, and fullerenes. In proportion to its thickness, it is about 100 times stronger than the strongest steel.<\/div>\n

” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]”>graphene<\/span>: superconductivity that can be turned on and off with an electric pulse, much like a light switch. To accomplish this, they used some meticulous twisting and stacking of layers of graphene and boron nitride.<\/p>\n

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The discovery could lead to ultrafast, energy-efficient superconducting transistors for neuromorphic devices \u2014 electronics designed to operate in a way similar to the rapid on\/off firing of neurons in the human brain.<\/p>\n

Magic-angle graphene refers to a very particular stacking of graphene \u2014 an atom<\/p>\n

An atom is the smallest component of an element. It is made up of protons and neutrons within the nucleus, and electrons circling the nucleus.<\/div>\n

” data-gt-translate-attributes=”[{"attribute":"data-cmtooltip", "format":"html"}]”>atom<\/span>-thin material made from carbon atoms that are linked in a hexagonal pattern resembling chicken wire. When one sheet of graphene is stacked atop a second sheet at a precise \u201cmagic\u201d angle, the twisted structure creates a slightly offset \u201cmoir\u00e9\u201d pattern, or superlattice, that is able to support a host of surprising electronic behaviors.<\/p>\n

In 2018, Pablo Jarillo-Herrero and his group at MIT were the first to demonstrate magic-angle twisted bilayer graphene. They showed that the new bilayer structure could behave as an insulator, much like wood, when they applied a certain continuous electric field. When they upped the field, the insulator suddenly morphed into a superconductor, allowing electrons to flow, friction-free.<\/p>\n

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That discovery was a watershed in the field of \u201ctwistronics,\u201d which explores how certain electronic properties emerge from the twisting and layering of two-dimensional materials. Researchers including Jarillo-Herrero have continued to reveal surprising properties in magic-angle graphene, including various ways to switch the material between different electronic states. So far, such \u201cswitches\u201d have acted more like dimmers, in that researchers must continuously apply an electric or magnetic field to turn on superconductivity, and keep it on.<\/p>\n

Now Jarillo-Herrero and his team have shown that superconductivity in magic-angle graphene can be switched on, and kept on, with just a short pulse rather than a continuous electric field. The key, they found, was a combination of twisting and stacking.<\/p>\n

In a paper published on January 30 in the journal Nature Nanotechnology<\/em>, the team reports that, by stacking magic-angle graphene between two offset layers of boron nitride \u2014 a two-dimensional insulating material \u2014 the unique alignment of the sandwich structure enabled the researchers to turn graphene\u2019s superconductivity on and off with a short electric pulse.<\/p>\n

\u201cFor the vast majority of materials, if you remove the electric field, zzzzip, the electric state is gone,\u201d says Jarillo-Herrero, who is the Cecil and Ida Green Professor of Physics at MIT. \u201cThis is the first time that a superconducting material has been made that can be electrically switched on and off, abruptly. This could pave the way for a new generation of twisted, graphene-based superconducting electronics.\u201d<\/p>\n

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His MIT co-authors are lead author Dahlia Klein PhD \u201921, graduate student Li-Qiao Xia, and former postdoc David MacNeill, along with Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan.<\/p>\n

Flipping the switch<\/strong><\/p>\n

In 2019, a team at Stanford University discovered that magic-angle graphene could be coerced into a ferromagnetic state. Ferromagnets are materials that retain their magnetic properties, even in the absence of an externally applied magnetic field.<\/p>\n

The researchers found that magic-angle graphene could exhibit ferromagnetic properties in a way that could be tuned on and off. This happened when the graphene sheets were layered between two sheets of boron nitride such that the crystal structure of the graphene was aligned to one of the boron nitride layers. The arrangement resembled a cheese sandwich in which the top slice of bread and the cheese orientations are aligned, but the bottom slice of bread is rotated at a random angle with respect to the top slice. The result intrigued the MIT group.<\/p>\n

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\u201cWe were trying to get a stronger magnet by aligning both slices,\u201d Jarillo-Herrero says. \u201cInstead, we found something completely different.\u201d<\/p>\n

In their current study, the team fabricated a sandwich of carefully angled and stacked materials. The \u201ccheese\u201d of the sandwich consisted of magic-angle graphene \u2014 two graphene sheets, the top rotated slightly at the \u201cmagic\u201d angle of 1.1 degrees with respect to the bottom sheet. Above this structure, they placed a layer of boron nitride, exactly aligned with the top graphene sheet. Finally, they placed a second layer of boron nitride below the entire structure and offset it by 30 degrees with respect to the top layer of boron nitride.<\/p>\n

The team then measured the electrical resistance of the graphene layers as they applied a gate voltage. They found, as others have, that the twisted bilayer graphene switched electronic states, changing between insulating, conducting, and superconducting states at certain known voltages.<\/p>\n

What the group did not expect was that each electronic state persisted rather than immediately disappearing once the voltage was removed \u2014 a property known as bistability. They found that, at a particular voltage, the graphene layers turned into a superconductor, and remained superconducting, even as the researchers removed this voltage.<\/p>\n

<\/span><\/span><\/span><\/p>\n

This bistable effect suggests that superconductivity can be turned on and off with short electric pulses rather than a continuous electric field, similar to flicking a light switch. It isn\u2019t clear what enables this switchable superconductivity, though the researchers suspect it has something to do with the special alignment of the twisted graphene to both boron nitride layers, which enables a ferroelectric-like response of the system. (Ferroelectric materials display bistability in their electric properties.)<\/p>\n

\u201cBy paying attention to the stacking, you could add another tuning knob to the growing complexity of magic-angle, superconducting devices,\u201d Klein says.<\/p>\n

For now, the team sees the new superconducting switch as another tool researchers can consider as they develop materials for faster, smaller, more energy-efficient electronics.<\/p>\n

\u201cPeople are trying to build electronic devices that do calculations in a way that\u2019s inspired by the brain,\u201d Jarillo-Herrero says. \u201cIn the brain, we have neurons that, beyond a certain threshold, they fire. Similarly, we now have found a way for magic-angle graphene to switch superconductivity abruptly, beyond a certain threshold. This is a key property in realizing neuromorphic computing.\u201d<\/p>\n

<\/span><\/span><\/span><\/p>\n

Reference: \u201cElectrical switching of a bistable moir\u00e9 superconductor\u201d by Dahlia R. Klein, Li-Qiao Xia, David MacNeill, Kenji Watanabe, Takashi Taniguchi and Pablo Jarillo-Herrero, 30 January 2023, Nature Nanotechnology<\/em>.
DOI: 10.1038\/s41565-022-01314-x<\/a><\/p>\n

This research was supported in part by the U.S. Air Force Office of Scientific Research, the U.S. Army Research Office, and the Gordon and Betty Moore Foundation.<\/p>\n

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