Physicists report promising approaches to take advantage of exotic electronic behavior

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MIT physicists have discovered that moiré superlattices (pictured on the right) can be used to exploit exotic types of electronic behavior. The superlattice consists of two layers of graphene in an atomically thin layer (one layer on the left), which are placed on top of each other and rotated at a slight angle. Credits: Pablo Jarillo-Herrero et al. , WITH

Scientists have been working on using Bloch oscillations for about 50 years. This is an exotic type of electronic movement that has the potential to introduce new areas of physics and important new technologies. This is the same as traditional electronic watch movements, which make everything from smartwatches to computers powerful enough. To take us to the moon

MIT physicists are now reporting a new approach to achieving the recently introduced Bloch oscillation. Graphene superlattice. Graphene, a material made up of a single layer of carbon atoms arranged in a hexagon similar to a honeycomb structure, is an excellent electrical conductor. This is Electronic Properties It goes through an interesting transformation in the presence of an “electrical network” (periodic potential) . resulting in a novel electron behavior not found in the original material. In a recent issue of Physical review letterScientists outline why graphene superlattices become game changers when tracking Bloch oscillations.

Usually electrons that are exposed to a constant electric field accelerate linearly. Quantum Mechanics We predict, however, that materials consisting of electrons in a crystal or regularly arranged atoms can behave differently. When exposed to electric fields, they can vibrate with small waves or Bloch oscillations. “This amazing behavior is a symbolic example of coherent dynamics in quantum many-body systems,” said Leonid Levitov, professor of physics at MIT and current head of research. Levitov is also connected to the MIT materials laboratory.

Other authors are Ali Fahimniya and Zhiyu Dong, physics students at MIT, and Egor I. Kiselev from the Karlsruhe Institute of Technology.

For new applications

It is important that Bloch oscillations occur for all electrons with the same frequency value and that they can be adjusted by the applied electric field. In addition, typical frequency values ​​(terahertz range or trillion cycles per second) are in a range that is difficult to access using conventional means. Today’s electronics and optics work at frequencies below or above terahertz. “The terahertz frequency is in the middle and does not benefit as much as the other spectra,” says Levitov. “With easy access to them, there could be many uses, from better non-invasive security scans at airports to developing new electronics.”

Over the years, many scientists have tried to demonstrate its behavior due to the interesting physics and possible applications of Bloch’s oscillation. However, Bloch oscillations are very sensitive to the scattering process of materials due to lattice vibrations (phonons) and disorder. As a result, early research into creating Bloch oscillations was very important, but an approach that relied on semiconductor superlattices led to the Nobel Prize and modern solid-state lasers, but to the original goal. It was only a limited success over. “People saw signs of Bloch vibrations in these systems, but not at a practical level. Inevitably there was a phase of relaxation that turned out to be pretty terrible. [for the phenomenon]“Says Levitow.

New material

Enter a new material called Moiré Graph. Moire graph was developed by physics professor Pablo Jarillo-Herrero at MIT and consists of two layers of atomically thin graph that are stacked and rotated at a slight angle. “And according to theory, this material should be an ideal candidate for seeing Bloch oscillations,” says Levitov. In a recent paper, he and his colleagues analyzed material parameters that affect how electrons move in them and how chaotic it is: “Moiré graphene is a semiconductor for all reasons. It shows that it is equal to or better than the superlattice. ”

In addition, other attractive types of superlattices have recently appeared. These include graphene paired with hexagonal boron nitride or a structured dielectric superlattice. Among the added benefits, graphene superlattices are much easier to create than the complex complex structures of previous studies. “These systems were only made by a small number of talented groups around the world,” says Levitov. Moiré graphene is already being produced by several corporations in the USA alone and by many other corporations around the world.

Finally, Levitov et al. State that moiré graphs meet another important criterion for the practical use of Bloch oscillations. The electrons involved in the oscillation do so at the same terahertz frequency, but without a little help, they do so independently of each other. It is important that they vibrate synchronously. “If we could do that, we would essentially be moving from a one-electron phenomenon to a microscopic vibration. The macroscopic oscillation is a source of microscopic current, which makes it easy to see and very easy to use, ”says Levitov. Increase. Scientists believe that moiré graphene electrons should be very suitable for synchronization using standard techniques.

Dmitri Basov, professor at Columbia University and dean of physics, commented: Bloch oscillation of the moiré flat band system, but we definitely try. Basov was not involved in the work on in. was reported Physical review letter..

Levitov is excited to continue working with MIT students. “The best of it will come later when we look at the experimental results that back up the idea,” he says.


New beat of quantum materials


For more informations:
Ali Fahimniya et al., Synchronization of Bloch Oscillation-Free Carriers in Moiré Flat Bands, Physical review letter (2021). DOI: 10.1103 / PhysRevLett.126.256803

Provided by
Massachusetts Institute of Technology Materials Research Institute

Quote: Physicists, Get Exotic Electronic Behavior on October 5, 2021 from https://phys.org/news/2021-10-physicists-approach-harnessing-exotic-electronic.html (October 2021) 5th) reports a promising approach advantage from

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Physicists report promising approaches to take advantage of exotic electronic behavior

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