Valley symmetry breaking and gap tuning in graphene by spin doping

TL;DR

This paper investigates how spin doping in graphene creates valley-specific gaps and enables independent tuning of electronic properties, leading to novel quantum Hall phenomena and distinctive optical conductivities.

Contribution

It introduces a model for graphene with spin textures that breaks valley symmetry and allows independent gap tuning, revealing new quantum Hall effects.

Findings

Valley symmetry is broken by spin doping creating tunable gaps.

Independent control of valley gaps leads to two Hall plateaux.

Logarithmic singularity in Hall conductivity at gap resonance.

Abstract

We study graphene with an adsorbed spin texture, where the localized spins create a periodic magnetic flux. The latter produces gaps in the graphene spectrum and breaks the valley symmetry. The resulting effective electronic model, which is similar to Haldane's periodic flux model, allows us to tune the gap of one valley independently from that of the other valley. This leads to the formation of two Hall plateaux and a quantum Hall transition. We discuss the density of states, optical longitudinal and Hall conductivities for nonzero frequencies and nonzero temperatures. A robust logarithmic singularity appears in the Hall conductivity when the frequency of the external field agrees with the width of the gap.