Scattering of magnons at graphene quantum-Hall-magnet junctions

TL;DR

This paper investigates how magnons scatter at graphene quantum-Hall-magnet junctions with different filling factors, revealing conditions for weak or blocked scattering and proposing methods to probe QHM states.

Contribution

It provides a theoretical analysis of magnon scattering at QHM junctions, highlighting the effects of junction symmetry and filling factors, and suggests new ways to probe QHM states using valley-waves and magnons.

Findings

Magnons are weakly scattered in the $ u=1|-1|1$ geometry.

Scattering is chiral when the junction lacks mirror symmetry.

Magnon transmission is blocked beyond a critical incident angle in the $ u=1|0|1$ geometry.

Abstract

Motivated by recent non-local transport studies of quantum-Hall-magnet (QHM) states formed in monolayer graphene's $N=0$ Landau level, we study the scattering of QHM magnons by gate-controlled junctions between states with different integer filling factors $\nu$. For the $\nu=1|-1|1$ geometry we find magnons are weakly scattered by electric potential variation in the junction region, and that the scattering is chiral when the junction lacks a mirror symmetry. For the $\nu=1|0|1$ geometry, %in which the scattering region contains a $\nu=0$ canted antiferromagnet, we find that kinematic constraints completely block magnon transmission if the incident angle exceeds a critical value. Our results explain the suppressed non-local-voltage signals observed in the $\nu=1|0|1$ case. We use our theory to propose that valley-waves generated at $\nu=-1|1$ junctions and magnons can be used in combination to probe the spin/valley flavor structure of QHM states at integer and fractional filling factors.