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Examinations reveal exotic quantum states in a two-layer graphene



  Examinations reveal exotic quantum states in a two-layer graphene
In a two-layer structure of graphene, a new type of new particle is discovered. This so-called composite farm consists of one electron and two different types of magnetic fluxes, illustrated as blue and golden arrows in the figure. Composite farms are capable of forming pairs, such a unique interaction leading to the experimental discovery of the unexpected new quantum phenomena of Hall. Sincerely: Michelle Miller and Jia Li / Brown University
Researchers at the universities of Brown and Colombia have demonstrated previously unidentified states of matter that arise in double layers of graphene, two-dimensional nanomaterials. These new states, known as Hall's fractional quantum effect, derive from the complex interactions of electrons both in the graphite layers and in them.


"The findings show that aligning 2-D materials together in close proximity generates entirely new physics," says Lee Lee, a physics assistant at Brown, who initiates this work as a post-doc in Colombia working with Cory Dean, Professor of Physics, and Jim Hoon, Professor of Mechanical Engineering. "From the point of view of engineering materials, this work shows that these layered systems can be viable in creating new types of electronic devices that benefit from these new quantum states of Hall." Nature Physics It is important, says Haun, Wang Fung-Jen, a professor of mechanical engineering at Columbia Engineering, that some of these new quantum states of Hall "can be useful in creating fault-resistant quantum computers. "

The Hall effect occurs when a magnetic field is applied to a conductive material in a perpendicular direction to a current flow. The magnetic field causes a deflection of the current, creating tension in the transverse direction called tension in the Hall. The strength of Hall tension increases with the force of the magnetic field. The quantum version of the Hall effect was first discovered in experiments conducted in 1980 at low temperatures and strong magnetic fields. Experiments have shown that instead of increasing smoothly with the magnetic field, tension in Hall increases in a stepwise (or quantum) way. These steps are integer multiples of fundamental constants of nature and are completely independent of the physical composition of the material used in the experiments. The discovery was the 1985 Nobel Prize for Physics.

Several years later, researchers working at temperatures close to absolute zero and very strong magnetic fields found new types of quantum states of Hall in which the quantum steps in the tension of Hall correspond to fractional numbers, hence the name of the fractional quantum effect of Hall. The discovery of Hall's fractional quantum effect won another Nobel Prize in 1998. Later, theorists claim that Hal's fractional quantum effect is related to the formation of quasi-particles called composite farms. In this state, each electron is combined with a quantum of magnetic flux to form a composite fermion carrying a portion of an electron charge that results in Hall's fractional values. phenomena observed in single quantum well systems. This new study uses a two-layer graphite to investigate what happens when two quantum wells get closer together. The theory suggested that the interaction between two layers would lead to a new type of composite farm, but this was never observed in the experiment.

For the experiments, the team has built a multi-year work in Colombia to improve the quality of graphene devices that create ultra-pure devices entirely from atomic flat 2-D materials. The core of the structure consists of two graphite layers separated by a thin layer of hexagonal boron nitride as an insulating barrier. The two layer structure is encapsulated by hexagonal boron nitride as a protective isolator, and graphite as a conducting door to change the density of the charge carrier into the channel.

Once again the incredible versatility of graphene allowed us to push boundaries to the structures of the devices beyond what was possible before. "Dean, a professor of physics at Columbia University, said:" The accuracy and variability we can make these devices now allows us to explore a whole field of physics that was just considered completely inaccessible. "

The structures the graphene were exposed to strong magnetic fields – millions of times stronger than the Earth's magnetic field – the research produced a number of partial quantum states of Hall, some of which demonstrated excellent agreement with the composite farm model, and some that were never predicted us or observed.

"In addition interlayer composite fermions, monitor and other features that may need to be explained in the framework of the composite fermionen model," says Qianhui Shi, first author of the report and researcher at Columbia. "A closer study has revealed that, to our surprise, these new conditions are the result of pairing between composite farms." Pairing the interaction between adjacent layers and within the same layer leads to a variety of new quantum phenomena, making the inspiring platform two sides graphene "

" Of particular interest, "says Houn, there are several new states that have the potential to accept non-wavelength functions – states that do not fully match the traditional composite farm model." In non-aberrant states the electrons maintain some sort of "memory" for their past positions with each other, and this has the potential to enable quantum computers that do not require error correction, which is now a major stumbling block in this area. These are the first new candidates for non-Able States for 30 years, "Dean said," It's really exciting to see a new physique from our experiment. "

The study is titled" Joints of Composite Fermions in a Two-layer Graphene. "
Graphite offers a new quantum surprise


More Information:
J.I. A. Li et al., Connective Conditions of Composite Fermions in Two-Grain Graphen, Nature Physics (2019). DOI: 10.1038 / s41567-019-0547-z

Provided by
School of Engineering and Applied Sciences at Columbia University

References :
Research reveals exotic quantum states in a two-layer graphene (2019, June 26)
restored on 26 June 2019
by https://phys.org/news/2019-06-reveals-exotic-quantum-states-double-layer.html

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