Japanese researchers have described in different configurations heterostructure consisting of double-layer graphene and hexagonal boron nitride, and have found a way to manage its symmetry and the associated parameter — the curvature of the berry. This material may find application in the promising field of quantum electronics — politronica. The results published in the journal Physical Review B.
To increase the efficiency of modern chips, the scientists try to make their components as little as possible. However, to reduce the size of components to infinity does not allow physical limitations, so researchers are looking for alternative approaches to improving the performance of such devices based on other physical principles. One such area is politronica, in which the “zeros” and “units” are the minima of the energy valleys of conduction electrons. The presence of the electron in this or that valley, encodes a zero or a one. Electrons can also move between the valleys under the action of the quantum Hall effect, which consists in quantization of the voltage when the current flow in the sample. When physicists discovered this kind of Hall effect, they believed that its driving force — a strong magnetic field.
However, subsequent studies showed that the reason the curvature of the berry — artificial magnetic flux within the material, which is created through the movement of charged particles inside the crystal lattice. Unlike the magnetic field which acts on the material from the outside, the curvature of the berry acts from the inside, causing the electrons in the material to jump between the valleys. This option depends first of all from being violated if the material symmetry relative to time reversal and inversion of coordinates. The stronger the observed violations of these symmetries, the higher the curvature of the berry and stronger quantum Hall effect.
One of the most promising materials for politronika in which there is a high degree of violation of the symmetry with respect to inversion of coordinates of double — layer graphene. However, this material proved to be extremely sensitive to impurity atoms, which can get it from the environment. For protection double-layer graphene scientists have suggested that the use of monolayers of hexagonal boron nitride, which, like graphene consists of interconnected hexagons. Due to the polarity of the bonds of boron with nitrogen, the BN layer may alienate the impurity atoms, preventing their sorption by graphene. But still, it was not clear how adding these additional layers affects the berry curvature of bilayer graphene.
Physics the Japanese national Institute of advanced industrial science and technology under the guidance of senior teacher of Muruganathan Manoharan (Manoharan Muruganathan) investigated heterostructures consisting of two graphene layers, and one or two layers of boron nitride. The authors experimented with the position of these layers relative to each other, resulting in the received values of different polarity, and the curvature of the berry. Researchers have shown that for a system in which double-layer graphene placed on a monolayer hexagonal boron nitride, an increase of the curvature of the berry, resulting from the symmetry breaking of the inversion of coordinates. This experimental fact scientists explained that outside of the graphene layers of various forces, which change the mutual orientation of the layers and, as a consequence, the symmetry.