Fermi arc

In the field of unconventional superconductivity, a Fermi arc is a phenomenon visible in the pseudogap state of a superconductor. Seen in momentum space, part of the space exhibits a gap in the density of states, like in a superconductor. This starts at the antinodal points, and spreads through momentum space when lowering the temperature until everywhere is gapped and the sample is superconducting. The area in momentum space that remains ungapped is called the Fermi Arc