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Physicists find that misaligned carbon sheets give dissimilar properties



Physicists find that misaligned carbon sheets give dissimilar properties

Graphene is a single layer of carbon atoms arranged according to a flat honeycomb design, where each hexagon is formed by six carbon atoms at its vertices. UT Dallas physicists are studying the electrical properties that come out when two layers of graphene are stacked. Credit: University of Texas at Dallas

A material made of two layers of thick carbon — one atom has attracted the attention of physicists worldwide for its intriguing ̵

1; and potentially exploitable conductive properties.

Dr. Fan Zhang, assistant professor of physics at the School of Natural Sciences and Mathematics at the University of Texas at Dallas, and doctoral student in physics Qiyue Wang published an article in June with the group of Dr. Fengnian Xia at Yale University in Photonics of Nature describing how the ability of graphene curved with a graphene coating to carry an electric current with changes in reaction to infrared light.

One to Two Layers

Graphene is a single layer of carbon atoms arranged according to a flat honeycomb design, where each hexagon is formed by six carbon atoms at its vertices. Since the first isolation of graphene in 2004, its unique properties have been intensively studied by scientists for potential use in advanced computers, materials and devices.

If two sheets of graphene are stacked on top of each other, and one layer is rotated so that the layers are slightly out of alignment, the resulting physical configuration, called a graphene with a twisted coating, gives significantly different electronic properties. from those exhibited by a single layer or by two aligned layers.

“Graphene has been interesting for about 15 years,” Zhang said. “One layer is interesting to study, but if we have two layers, their interaction should make physics much richer and more interesting. That’s why we want to study two-layer graphene systems.”

A New Field Is Being Created

When the graphene layers are misaligned, a new periodic pattern emerges in the net, called a moire pattern. The moiré design is also hexagonal, but can be made up of more than 10,000 carbon atoms.

“The angle at which the two layers of graphene are misaligned – the twist angle” is of critical importance to the electronic properties of the material, “Wang said.” The smaller the angle of the graphene. the greater the periodicity of the moire. “

The unusual effects of specific twist angles on electron behavior were first proposed in a 2011 article by Dr. Allan MacDonald, a physics professor at UT Austin, and Dr. Rafi Bistritzer. . Zhang saw the birth of this field as a doctoral student in MacDonald’s group.

“At the time, others really didn’t pay attention to theory, but now it has become arguably the hottest topic in physics,” Zhang said.

In that 2011 research MacDonald and Bistritzer predicted that the kinetic energy of electrons could disappear into a misaligned graphene bilayer with a so-called “magic angle” of 1.1 degrees. In 2018, researchers at the Massachusetts Institute of Technology demonstrated this theory and found that offsetting two layers of graphene at 1.1 degrees produced a two-dimensional superconductor, a material that conducts electric current without resistance and without loss of energy.





This animation shows what happens when two layers of stacked graphene are misaligned with a small amount called a twist angle. A new periodic design appears in the mesh, called a moiré design. UT Dallas physicists are investigating how the twist angle affects the electronic properties of bi-twisted graphene. Credit: University of Texas at Dallas

In a 2019 article in Science Advances, Zhang and Wang, along with Dr. Jeanie Lau’s group at Ohio State University, showed that when offset by 0.93 degrees, graphene twisted with a brown coating shows both a superconducting and insulating state, thus broadening the magic angle significantly.

“In our previous work, we saw superconductivity as well as insulation. That’s what makes the study of coated graphene twisted like a hot field – superconductivity. The fact that you can manipulate pure carbon for superconducting is amazing and unprecedented, “Wang said.

Dallas UT New Findings

In his most recent research in Nature Photonics, Zhang and his collaborators at Yale investigated and how graphene interacts and interacts with the coating twisted with infrared light, which humans cannot see but can detect as heat.

“The interactions between light and matter are useful in many devices – for example, converting the sun into electrical energy,” Wang said. “Almost every object emits infrared light, including people, and this light can be detected by a device.”

Zhang is a theoretical physicist, so he and Wang set out to determine how infrared light can affect the conductance of electrons in graphene with curved sandpaper. Their work involved calculating light absorption based on the structure of the moire band, a concept that determines how electrons move in a quantum material mechanically.

“Graphene has been of interest for about 15 years. One layer is interesting to study, but if we have two layers, their interaction should make physics much richer and more interesting. That’s why we want to study graphene systems. with the shell, “he says.

“There are standard ways to calculate the band structure and light absorption in a regular crystal, but this is an artificial crystal, so we had to come up with a new method,” Wang said. Using the resources of the Texas Advanced Computer Center, a supercomputer facility at the UT Austin campus, Wang calculated the structure of the band and showed how the material absorbs light.

The Yale group has manufactured devices and conducted experiments showing that the mid-infrared photoresponse – the increase in conductivity due to glowing light – was exceptionally strong and the largest at a 1.8 degree twist. The sharp response ended at a twist angle of less than 0.5 degrees.

“Our theoretical results not only fit well with the experimental findings, but also pointed towards a mechanism that is fundamentally linked to the period of the moiré model, which in itself is connected to the angle of twist between the two layers of the graphene, “Zhang said.

The next step

“The twist angle is clearly very important in determining the properties of shell-twisted graphene,” Zhang added. “The question arises: Can we apply this to tune other two-dimensional materials to have unprecedented characteristics? Also, can we combine the response and superconductivity in graphene with the curved coating? For example, can you shine the light or do you focus on superconductivity in some way? That will be very interesting to study. “

“This new advancement could potentially enable a new class of high-sensitivity graphene-based infrared detectors,” said Dr. Joe Qiu, program manager for solid-state electronics and electromagnetics at the Office. of the United States Army Research (ARO), an element of the Army Research Laboratory for the Development of Combat Capabilities in the United States Army. “These new detectors could potentially affect applications such as night vision, which is of critical importance to the U.S. Army.”


Physicists make a discovery of graphene that can help develop superconductors


More information:
Bingchen Deng et al. Infrared infra-graphene mid-infrared response in graphene with small-angle coating with small surface, Photonics of Nature (2020). DOI: 10.1038 / s41566-020-0644-7

Provided by the University of Texas at Dallas



Citation: Physicists find misaligned carbon sheets with unmatched property performance (2020, 31 July) obtained on 31 July 2020 from https://phys.org/news/2020-07-physicists- misaligned-carbon-sheets-yield.html

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