Fermi arcs formation in Weyl semimetals: the key role of intervalley interaction

We propose an analytical model describing Fermi arc surface states observed in the recent investigations of Weyl semimetals. The effective two-valley Hamiltonian is supplemented by the boundary conditions taking into account both the intravalley and intervalley interfacial interaction. We demonstrate that the latter is crucial for the formation of the surface states having the form consistent with the experimental data. Depending on the magnitude and interplay between the intravalley and intervalley interactions, the Fermi arc connects two nearby or distant valleys. Moreover, the emergence of additional Fermi contours (closed curves not intersecting the Weil points) can be understood in the simplest four-valley approximation. These results open the opportunities for search of new effects in Weyl semimetals under the external fields.