Omnidirectional transmission and reflection of pseudospin-1 Dirac fermions in a Lieb superlattice

•The Dirac fermions in a Lieb superlattice are studied for the first time.•The energy spectra and transport properties are analytically obtained.•A transformation from omnidirectional transmission to reflection is realized.•An experimentally measurable switch behavior for conductance is predicted.

We study the behavior of pseudospin-1 Dirac fermions in a Lieb lattice subjected to an external periodic potential. It is found that there exists a zero-averaged wave-number passband at the incident energy corresponding to half of the potential step, in contrast to zero-averaged wave-number gap in graphene superlattices. By tuning the sublattice site-energy, the passband can be turned into an omnidirectional gap. Consequently, a transformation from omnidirectional transmission to reflection, accompanied with a switch of conductance from maximum to zero can be realized easily. It is expected that the controllable properties are useful for some applications in optical or electronic devices.