  Fermi-arc surface states of Weyl semimetals exhibit a unique combination of
localization to a surface and connectivity to the bulk Weyl fermions that can
move along the localization direction. We predict anomalous quantum-oscillation
signatures of Fermi arcs in the tunnel mangetoconductance across an interface
between two Weyl semimetals. These oscillations stem from a momentum-space
analog of Aharonov-Bohm interference of electrons moving along the interface
Fermi arcs, driven by an external magnetic field normal to the interface. The
Fermi arcs' connectivity to the bulk enables their characterization via
transport normal to the interface, while their localization manifests in a
strong field-angle anisotropy of the oscillations. This combination
distinguishes these anomalous oscillations from conventional Shubnikov-de Haas
oscillations and makes them identifiable even in complex oscillation spectra of
real materials.
