Signature of valley polarization in fractional flux periodicity of a graphene ring

TL;DR

This paper investigates how valley polarization and Coulomb interactions influence the energy spectrum, persistent current, and optical absorption in graphene quantum rings, revealing fractional flux periodicity and observable effects.

Contribution

It demonstrates the impact of Coulomb interactions on ground state transitions and flux periodicity, highlighting the role of valley polarization in graphene rings.

Findings

Interaction causes additional level crossings and fractional flux periodicity.

Persistent current exhibits extra steps due to Coulomb effects.

Optical absorption spectrum shows intricate structures linked to ground state changes.

Abstract

We have studied the interplay of valley polarization and the Coulomb interaction on the energy spectrum, persistent current, and optical absorption of a graphene quantum ring. We show that the interaction has a dramatic effect on the nature of the ground state as a function of the magnetic flux, and that the absence of the exchange interaction in opposite valleys means that the singlet-triplet degeneracy is not lifted for certain states. The additional level crossings (fractional flux periodicity) due to the interaction directly leads to extra steps in the persistent current and intricate structures in the absorption spectrum that should be experimentally observable. By varying the width of the ring, the nature of the ground state at zero field can be varied as well and this is manifest in the measurable properties we discuss.