Ingrid Fadelli is a writer for the website Phys.org.
Researchers at the Weizmann Institute of Science, the Barcelona Institute of Science and Technology, and the National Institute for Material Science in Tsukuba, Japan, have recently investigated a Berry-curvature magnetism in magic-angle graphene. Their paper was published in Nature physics.
Matan Bocarsly, one of the researchers who carried out the study, said that magic angle twisted bilayer graphene has drawn a huge amount of interest over the past few years due to its accessible flat bands.
The Hall effect is a charge transport related phenomenon in which a material's Hall resistance is quantized. Bocarsly and his colleague had studied the effect extensively in their previous works.
The researchers decided to use the measurement tools that they found to be most effective to further investigate the quantum Hall effect. The SQUID was fabricated on the apex of a pipette and was used to do this. The device is very sensitive and can measure magnetic fields in the 100nanometer scale.
The response of the local magnetic field was measured by varying the carrier density of the sample. The magnetic response is correlated with the internal magnetization of the wave functions, which is caused by the Berry curve. We have a local probe that is able to measure the Berry curve.
It is a very difficult task to directly measure the magnetism caused by local Berry curvature. The weak signal makes it hard for most existing Magnetic measurement tools to work.
Bocarsly and his colleagues were the first to measure it. They were able to identify a new disorder in the sample that they observed.
The top of an electronic system is thought to be a global invariant. The C number alternates between +2 and -1 on a device scale. There is a new type of disorder that needs to be accounted for in the fabrication of devices.
A recent study done by this team of researchers greatly contributes to the understanding of the magnetism of the area. It could inform the development of more precise theoretical models of this material, as well as possibly facilitating its implementation in various quantum computing devices.
Bocarsly said that the probe can be used to investigate other properties. There are still many unanswered questions about the symmetries that they obey, which is an interesting direction for future exploration.
More information: Sameer Grover et al, Chern mosaic and Berry-curvature magnetism in magic-angle graphene, Nature Physics (2022). DOI: 10.1038/s41567-022-01635-7 Journal information: Nature PhysicsThere is a science network.
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