Physicists discover important new property for graphene
Researchers have discovered in a graphite crystal the quantum Hall effect, which is characteristic only of 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 in the hundreds..
Over the past 15 years, much research has focused on the properties of graphene, and its three-dimensional predecessor has faded into the background. However, a team of scientists from the University of Manchester, studying devices made from defect-free chipped graphite crystals, discovered several at once. unexpected fundamental material properties.
Physicists have created a quality graphite crystal from individual sheets of graphene and enclosed it in hexagonal boron nitride, giving them the shape of a bar. Further along it was passed a small charge and a strong magnetic field is applied perpendicular to the plane of the rod. After measuring the generated longitudinal and transverse stresses, the scientists were surprised to find the quantum Hall effect, because the samples under study were thick enough and had to behave like an ordinary bulk semimetal, in which Hall resistance should not occur..
According to the team, KEH related to by the fact that a magnetic field forcing electrons move in limited dimension, and conductivity is possible only in a direction parallel to it. In sufficiently thin samples, this is one-dimensional displacement can become quantized through education stationary waves electrons. As a result, the material turns into a two-dimensional system with discrete energy levels..
Another surprise was that the quantum Hall effect was very sensitive to the parity of graphene layers. This is due to the fact that electrons of two types (flavors) also arise in graphite. Each of them forms its own waves, which are distributed among the layers alternately. In samples with an even number of layers, they are equally divided, so the energies of different types coincide. However, in odd ones, a shift of the energy levels of waves of different flavors relative to each other arises, and energy gaps of the QHE are formed.
The researchers also say they observed the fractional quantum Hall effect in thin graphite at 0.5 K, which is the result of strong interactions between electrons that are associated with superconductivity, magnetism, and superfluidity..
Team intends to hold and other experiments to better explore the theoretical basis, and also begin to study the properties of rhombohedral graphite.
We also previously reported that physicists discovered exotic spiral electrons.
text: Ilya Bauer, photo: filmsphotoartetc, wallpaperup