Planar Dirac diffusion

TL;DR

This paper investigates how Dirac particles diffuse in a planar setup with step and barrier potentials at arbitrary angles, revealing spin flip phenomena and their specific behaviors in transmission and reflection.

Contribution

It provides a detailed analysis of spin flip effects in Dirac particle diffusion, highlighting unexpected cancellations in barrier transmission.

Findings

Spin flip occurs in both transmitted and reflected waves for step potentials.

No spin flip in transmitted barrier results, contrary to expectations.

Spin flip cancellation occurs for individual wave packets.

Abstract

We present the results of the planar diffusion of a Dirac particle by step and barrier potentials, when the incoming wave impinges at an arbitrary angle with the potential. Except for right-angle incidence this process is characterized by the appearance of spin flip terms. For the step potential, spin flip occurs for both transmitted and reflected waves. However, we find no spin flip in the transmitted barrier result. This is surprising because the barrier result may be derived directly from a two-step calculation. We demonstrate that the spin flip cancellation indeed occurs for each particle (wave packet) contribution.