The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips

TL;DR

This paper theoretically demonstrates that graphene's unique electronic structure enables a relativistic Fano spin-filter, allowing full spin polarization of conductance through STM tips, unlike conventional 2DEG systems.

Contribution

It introduces the concept of using Fano interference in graphene to achieve spin filtering, a novel approach not previously explored.

Findings

Graphene exhibits a diverging Fano factor, lifting spin degeneracy.

2DEG shows a zero Fano factor, maintaining spin degeneracy.

Full polarized conductance is achievable by adjusting STM tip position.

Abstract

We explore theoretically the density of states (LDOS) probed by an STM tip of 2D systems hosting an adatom and a subsurface impurity,both capacitively coupled to AFM tips and traversed by antiparallel magnetic fields. Two kinds of setups are analyzed, a monolayer of graphene and a two-dimensional electron gas (2DEG). The AFM tips set the impurity levels at the Fermi energy, where two contrasting behaviors emerge: the Fano factor for the graphene diverges, while in the 2DEG it approaches zero. As result, the spin-degeneracy of the LDOS is lifted exclusively in the graphene system, in particular for the asymmetric regime of Fano interference. The aftermath of this limit is a counterintuitive phenomenon, which consists of a dominant Fano factor due to the subsurface impurity even with a stronger STM-adatom coupling. Thus we find a full polarized conductance, achievable just by displacing vertically the position of the STM tip. To the best knowledge, our work is the first to propose the Fano effect as the mechanism to filter spins in graphene. This feature arises from the massless Dirac electrons within the band structure and allows us to employ the graphene host as a relativistic Fano spin-filter.