Quantum Interference Assisted Spin Filtering in Graphene Nanoflakes

Abstract

We demonstrate that hexagonal graphene nanoflakes with zigzag edges display quantum interference (QI) patterns analogous to benzene molecular junctions. In contrast with graphene sheets, these nanoflakes also host magnetism. The cooperative effect of QI and magnetism enables spin-dependent quantum interference effects that result in a nearly complete spin polarization of the current and holds a huge potential for spintronic applications. We understand the origin of QI in terms of symmetry arguments, which show the robustness and generality of the effect. This also allows us to devise a concrete protocol for the electrostatic control of the spin polarization of the current by breaking the sublattice symmetry of graphene, by deposition on hexagonal boron nitride, paving the way to switchable spin filters. Such a system benefits from all of the extraordinary conduction properties of graphene, and at the same time, it does not require any external magnetic field to select the spin polarization, as magnetism emerges spontaneously at the edges of the nanoflake.

Interplay between destructive quantum interference and symmetry-breaking phenomena in graphene quantum junctions

“…In our original proposal in Ref. 5, we showed that destructive QI can be used to generate nearly completely spin-polarized currents in the absence of magnetic fields or spin-orbit coupling, simply exploiting the spontaneous breaking of the SU (2) spin-rotational symmetry induced by electronic correlation in the presence of the edges. The present work extends the scope of our previous study to multi-component systems where other degrees of freedom (e.g., valley, orbital, layer) can be manipulated via an external handle lifting the symmetry.…”

“…In the PM state, the anti-resonance is pinned at the Fermi level ω QI = 0 due to the particle-hole symmetry of the spectrum. 5,58 In the AF state instead ω QI σ is spin-dependent and shifts below or above the Fermi level, proportionally to the average staggered magnetization S z . The detailed analysis of the transmission as a function of U/t shown in Fig.…”

“…This is detrimental to the formation of the AF state, and it results in a partial quench of the local magnetic moments. 5 A consequence of this interplay is that, if the system is on the verge of magnetic ordering, tuning ǫ could allow to drive the system through a crossover between phases with different charge and spin order, and ideally working as a switch between spin-filtering and valley-filtering effects.…”

Inducing and controlling magnetism in the honeycomb lattice through a harmonic trapping potential

“…In order to explore extensively the dependence of parameters we focus on finite artificial flakes, following previous calculations in a solid-state set-up [12,21]. We borrow from these works the choice to start from the 150-site cluster that we label as 5N (according to a notation where N is the number of sites on an edge).…”

The Anomalous Effect of Quantum Interference in Organic Spin Filters

“…24,25 But only few reports have described QI effects in systems exhibiting spin polarization. [26][27][28][29] Recently, Li et al proposed a mechanism for tuning the spin filtering ratio based on QI effects in a nickel based junction. 30 Ratner and coworkers have demonstrated that how DQI features can be controlled by addition of a donor or acceptor group to the polyacetylene chain bridging graphene nanoribbons (ZGNR).…”