The researchers discovered a quantum hall effect in a graphite crystal, which is characteristic only for two-dimensional systems. They also found that the material behaves differently depending on the parity of the graphene layers, even when their number is measured by hundreds.
For the past 15 years, many studies have been focused on studying the properties of graphene, and its three-dimensional predecessor departed to the background. However, a team of scientists from the University of Manchester, who studied the devices made from compatible crystals of graphite, not containing defects, opened several unexpected fundamental properties of the material.
Physicists created a high-quality graphite crystal from individual graphene sheets and concluded it in the hexagonal nitride of Bohr, giving them the form of Bar. Further, a small charge was passed along it and a strong magnetic field was applied, perpendicular to the rod plane. Measuring the generated longitudinal and transverse voltage, scientists were surprised by finding the quantum Hall effect, because the samples under study were quite thick and should have behaved as an ordinary bulk semimetal, in which Hall resistance should not occur.
According to the team, KEH is associated with the fact that the magnetic field forces electrons to move in a limited dimension, and conductivity is possible only in the direction parallel to it. In sufficiently thin samples, this one-dimensional movement may become quantized due to the formation of stationary electron waves. As a result, the material turns into a two-dimensional system with discrete energy levels.
Another surprise was the fact that the quantum effect of the Hall was very sensitive to the parity of the graphene layers. This is due to the fact that in graphite there are also electrons of two varieties (aromas). Each of them forms its own waves, which are distributed between the layers alternately. In samples with an even amount of layers of their equal, therefore the energy of various species coincide. However, in odd displacement of the energy levels of different flavors relative to each other, and the energy gaps of CEC are formed.
The researchers also say that a fractional quantum hall effect was observed in thin graphite at a temperature of 0.5 K, which is the result of strong interactions between electrons that are associated with superconductivity, magnetism and superfluidity.
The team intends to conduct other experiments to better explore the theoretical foundation, and will also begin to study the properties of rhombohedral graphite.
Previously, we also reported that physicists opened