Theory of proximity-induced exchange coupling in graphene on hBN/(Co, Ni)

URN zum Zitieren dieses Dokuments: urn:nbn:de:bvb:355-epub-348998

Zollner, Klaus, Gmitra, Martin, Frank, Tobias und Fabian, Jaroslav (2016) Theory of proximity-induced exchange coupling in graphene on hBN/(Co, Ni). Physical Review B (PRB) 94, S. 155441.

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Zusammenfassung

Graphene, being essentially a surface, can borrow some properties of an insulating substrate (such as exchange or spin-orbit couplings) while still preserving a great degree of autonomy of its electronic structure. Such derived properties are commonly labeled as proximity. Here we perform systematic first-principles calculations of the proximity exchange coupling, induced by cobalt (Co) and nickel (Ni) in graphene, via a few (up to three) layers of hexagonal boron nitride (hBN). We find that the induced spin splitting of the graphene bands is of the order of 10 meV for a monolayer of hBN, decreasing in magnitude but alternating in sign by adding each new insulating layer. We find that the proximity exchange can be giant if there is a resonant d level of the transition metal close to the Dirac point. Our calculations suggest that this effect could be present in Co heterostructures, in which a d level strongly hybridizes with the valence-band orbitals of graphene. Since this hybridization is spin dependent, the proximity spin splitting is unusually large, about 10 meV even for two layers of hBN. An external electric field can change the offset of the graphene and transition-metal orbitals and can lead to a reversal of the sign of the exchange parameter. This we predict to happen for the case of two monolayers of hBN, enabling electrical control of proximity spin polarization (but also spin injection) in graphene/hBN/Co structures. Nickel-based heterostructures show weaker proximity effects than cobalt heterostructures. We introduce two phenomenological models to describe the first-principles data. The minimal model comprises the graphene (effective) pz orbitals and can be used to study transport in graphene with proximity exchange, while the pz−d model also includes hybridization with d orbitals, which is important to capture the giant proximity exchange. Crucial to both models is the pseudospin-dependent exchange coupling, needed to describe the different spin splittings of the valence and conduction bands.

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Dokumentenart:

Artikel

Datum:

2016

Institutionen:

Physik > Institut für Theoretische Physik > Lehrstuhl Professor Richter > Arbeitsgruppe Jaroslav Fabian

Projekte:

SFB 689: Spinphänomene in reduzierten Dimensionen, GRK 1570, Elektronische Eigenschaften von Nanostrukturen auf Kohlenstoff-Basis, Graphene Flagship

Identifikationsnummer:

Wert	Typ
10.1103/PhysRevB.94.155441	DOI

Dewey-Dezimal-Klassifikation:

500 Naturwissenschaften und Mathematik > 530 Physik

Status:

Veröffentlicht

Begutachtet:

Ja, diese Version wurde begutachtet

An der Universität Regensburg entstanden:

Eingebracht am:

28 Nov 2016 14:16

Zuletzt geändert:

08 Mrz 2017 08:41

Dokumenten-ID:

34899

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