= Fermi surface
{c}
{wiki}
For noninteracting fermions at zero temperature, the Fermi surface is the momentum-space boundary $\epsilon(\mathbf k)=\mu$ between occupied and unoccupied states. Its shape can be a circle, several pockets or a more complicated surface, depending on the dispersion and filling.
In an interacting <Fermi liquid>, occupation is not simply zero or one on either side. Instead the momentum distribution has a discontinuity with quasiparticle weight $Z$, and low-energy <Landau quasiparticles> define the Fermi surface. This distinguishes a sharp quasiparticle boundary from an ideal-gas step distribution. The geometry controls low-energy phase space, transport and collective response. <Quantum oscillations> constrain extremal orbit areas, while momentum-resolved spectral measurements can probe excitations near the chemical potential; the interpretation requires the relevant interaction and measurement model.
Back to article page
