Coherent Nonreciprocal Valley Transport in Dirac/Weyl Semimetals

Abstract

Nonreciprocal electronic transport, characterized by directional asymmetry between forward and backward two-terminal responses, typically requires an intrinsic inversion-breaking feature in the host material or an applied field, such as magnetic order, magnetochiral coupling, polar lattice distortion, or a superconducting state. This study demonstrates that a single electrostatic barrier with a shape lacking inversion symmetry can induce coherent nonreciprocal transport in a Dirac or Weyl channel without these conventional requirements. The underlying mechanism is geometric: when a barrier possesses two qualitatively distinct refraction interfaces, specifically one vertical and one oblique, forward- and backward-propagating wave packets encounter different Fermi-surface-mismatch sequences at the entrance and exit faces. Coherent split-operator Dirac wave-packet simulations with realistic device parameters reveal that, in a channel with isotropic (untilted) energy dispersion, an inversion-asymmetric (right-angle) triangular barrier produces pronounced charge-mode rectification, confirming its geometric origin. Introducing a Dirac-cone tilt causes the same barrier shape to exhibit coherent, valley-resolved one-way transport, with the dichroic structure reversing sign across the Dirac point. Notably, a mirror-symmetric (isosceles) triangle with two oblique faces yields valley-polarized transmission while remaining exactly reciprocal. The combination of oblique interfaces and tilt alone is insufficient; the essential factor is the presence of a sequence of geometrically distinct interface types.