In summary, a Fermi surface is the boundary between occupied and unoccupied energy levels for electrons in a solid material at absolute zero temperature. It is closely related to electronic correlations and can provide valuable insights into the properties and behavior of materials. Electronic correlations can significantly alter the Fermi surface, and it can be measured experimentally using various techniques.
An increase in the number of Fermi pockets can reduce electronic correlations because it can lead to a more homogeneous distribution of electronic states. This means that electrons are less likely to interact with each other and show reduced correlation effects. Additionally, when multiple Fermi pockets exist, electrons may be able to avoid each other by occupying different pockets, thereby further reducing electronic correlations.