Note on lattice spin in graphene and "spin from isospin" phenomenon

TL;DR

This paper explores how the pseudospin in graphene, originating from its lattice structure, can behave like real angular momentum through a mechanism analogous to the "spin from isospin" phenomenon known in particle physics.

Contribution

It demonstrates that the lattice pseudospin in graphene can acquire properties similar to real angular momentum via a mechanism analogous to "spin from isospin" in particle physics.

Findings

Pseudospin in graphene can act as real angular momentum.

The "spin from isospin" mechanism applies to lattice pseudospin.

Internal symmetries influence angular momentum in graphene.

Abstract

It is well-known that the dynamics of low energy electron in graphene honeycomb lattice near the K/K' points can be described, in tight-binding approximation, by 2+1 massless Dirac equation. Graphene's spin equivalent, "pseudospin", arises from the degeneracy introduced by the honeycomb lattice's two inequivalent atomic sites per unit cell. Mecklenburg and Regan (Phys. Rev. Lett. 106 (2011), 116803) have shown that, contrary to the common view, the pseudospin has all attributes of real angular momentum. In some circumstances, the internal symmetries can produce an important contribution to angular momentum. This phenomenon has been known for many years in particle physics and called "spin from isospin". We show that similar mechanism works in the case of lattice pseudospin.