Fermion doubling theorems in 2D non-Hermitian systems for Fermi points and exceptional points

Understand

The fermion doubling theorem plays a pivotal role in Hermitian topological materials.

• It states, for example, that Weyl points must come in pairs in three-dimensional semimetals.
• Here, we present an extension of the doubling theorem to non-Hermitian lattice Hamiltonians.
• We focus on two-dimensional non-Hermitian systems without any symmetry constraints, which can host two different types of topological point nodes, namely, (i) Fermi points and (ii) exceptional points.