Coherent Nonreciprocal Valley Transport in Dirac/Weyl Semimetals

TL;DR

This paper demonstrates that a simple, inversion-asymmetric electrostatic barrier can induce nonreciprocal and valley-polarized transport in Dirac/Weyl semimetals through purely geometric effects, without magnetic or superconducting ingredients.

Contribution

It reveals a geometric mechanism for nonreciprocal valley transport in Dirac/Weyl semimetals using asymmetric barriers, independent of magnetic or superconducting effects.

Findings

A triangular barrier causes strong charge rectification due to geometric effects.

Tilted Dirac cones enable valley-resolved diode behavior with sign reversal across the Dirac point.

Mirror-symmetric triangles can produce valley-polarized transmission while remaining reciprocal.

Abstract

Nonreciprocal electronic transport, defined as a directional asymmetry between the forward and backward two-terminal responses, typically requires a built-in inversion-breaking feature of the host material or an applied field, such as magnetic order, magnetochiral coupling, polar lattice distortion, or a superconducting state. Here, we show that a single electrostatic barrier whose shape lacks inversion symmetry can drive coherent nonreciprocal transport in a Dirac or Weyl channel without any of these ingredients. The mechanism is geometric: across a barrier with two qualitatively distinct refraction interfaces (one vertical and one oblique), forward- and backward-propagating wave packets experience different Fermi-surface-mismatch sequences at the entrance and exit faces. Using coherent split-operator Dirac wave-packet simulations with realistic device parameters, we show that in a channel with isotropic (untilted) energy dispersion, an inversion-asymmetric (right-angle) triangular barrier produces strong charge-mode rectification, establishing its purely geometric origin. Adding a Dirac-cone tilt turns the same shape into a coherent valley-resolved diode whose dichroic structure flips sign across the Dirac point. Strikingly, a mirror-symmetric (isosceles) triangle with two oblique faces exhibits valley-polarized transmission while remaining exactly reciprocal. Oblique interfaces and tilt together do not suffice; the essential ingredient is a sequence of geometrically distinct interface types.