Nonreciprocal ballistic transport in multi-layer Weyl semimetal films with surface engineering

Weyl semimetal (WSM) thin films exhibit distinct electronic properties compared to their bulk counterparts. In this study, we theoretically investigate the nonreciprocal ballistic transport phenomena arising in WSM thin films due to surface modifications. Our analysis demonstrates that the nonreciprocity is sub-band-resolved, where the surface states provide the dominant contribution to the nonreciprocity, whereas the bulk states introduce a negative correction. Calculations further reveal a quantum size effect: overall, the nonreciprocal signal decreases with increasing film thickness, but it undergoes discontinuities as the Fermi energy approaches the bottom of a sub-band. Moreover, we observe that the density of states (DOS) in such multi-layer systems exhibits a thickness-independent pattern, which can be effectively explained by a single-variable theory.