Weyl fermions on a finite lattice

Abstract

The phenomenon of unpaired Weyl fermions appearing on the sole 2n-dimensional boundary of a (2n+1)-dimensional manifold with massive Dirac fermions was recently analyzed in a companion paper by one of the authors. In this Letter we show that similar unpaired Weyl edge states can be seen on a finite lattice. In particular, we consider the discretized Hamiltonian for a Wilson fermion in (2+1) dimensions with a 1+1 dimensional boundary and continuous time. We demonstrate that the low lying boundary spectrum is indeed Weyl-like: it has a linear dispersion relation and definite chirality and circulates in only one direction around the boundary. We comment on how our results are consistent with Nielsen-Ninomiya theorem. This work removes one potential obstacle facing the program for regulating chiral gauge theories recently proposed by one of the authors.

Comments: 5 pages, 4 figures. This version coincides with the version accepted for publication in Phys. Rev. Lett. on Jan. 26, 2024. Major changes include performing computations on a disk-shaped lattice instead of square, with corresponding changes in the figures. Supplemental material of the publication version has been included here as an appendix. Scientific conclusions have not changed