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Tunable Fermi level and hedgehog spin texture in gapped graphene.

Varykhalov A, Sánchez-Barriga J, Marchenko D, Hlawenka P, Mandal PS, Rader O - Nat Commun (2015)

Bottom Line: First, a giant Rashba effect (∼70 meV splitting) away from the Dirac point and, second, the breaking of the six-fold graphene symmetry at the interface.Surprisingly, the graphene Fermi level is systematically tuned by the Au concentration and can be moved into the bandgap.We conclude that the out-of-plane spin texture is not only of fundamental interest but can be tuned at the Fermi level as a model for electrical gating of spin in a spintronic device.

View Article: PubMed Central - PubMed

Affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489 Berlin, Germany.

ABSTRACT
Spin and pseudospin in graphene are known to interact under enhanced spin-orbit interaction giving rise to an in-plane Rashba spin texture. Here we show that Au-intercalated graphene on Fe(110) displays a large (∼230 meV) bandgap with out-of-plane hedgehog-type spin reorientation around the gapped Dirac point. We identify two causes responsible. First, a giant Rashba effect (∼70 meV splitting) away from the Dirac point and, second, the breaking of the six-fold graphene symmetry at the interface. This is demonstrated by a strong one-dimensional anisotropy of the graphene dispersion imposed by the two-fold-symmetric (110) substrate. Surprisingly, the graphene Fermi level is systematically tuned by the Au concentration and can be moved into the bandgap. We conclude that the out-of-plane spin texture is not only of fundamental interest but can be tuned at the Fermi level as a model for electrical gating of spin in a spintronic device.

No MeSH data available.


Effect of gating on the vectorial spin texture of graphene Fermi surface.Minor change of charge doping from (a) n-type to (b) p-type shifts Fermi level from the apex of upper gapped Dirac cone π* to the apex of lower cone π and switches the direction of out-of-plane spin while the in-plane spin texture remains unchanged. Red and green arrows sketch in-plane spins of Rashba split bands circulating in opposite directions. Black arrows denote hedgehog spins within the gap of the Dirac cone.
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f4: Effect of gating on the vectorial spin texture of graphene Fermi surface.Minor change of charge doping from (a) n-type to (b) p-type shifts Fermi level from the apex of upper gapped Dirac cone π* to the apex of lower cone π and switches the direction of out-of-plane spin while the in-plane spin texture remains unchanged. Red and green arrows sketch in-plane spins of Rashba split bands circulating in opposite directions. Black arrows denote hedgehog spins within the gap of the Dirac cone.

Mentions: The hedgehog spin texture becomes the key to spin functionality in the context of Fermi level tuning which is shown here by varying the Au concentration (Fig. 3a,b). Aligning the bandgap to the Fermi level also tunes the vectorial spin texture of the graphene Fermi surface at and valleys, as illustrated in Fig. 4. This, in turn, is highly relevant for the emerging field of valleytronics dealing with electronic devices based on valley-dependent Berry phase effects2830. In particular, spin-valley scattering in graphene with broken sublattice symmetry and non-equivalent magnetic moments of and valleys may be used for the creation of highly effective spin separators (see Supplementary Note 6 and Supplementary Figure 7).


Tunable Fermi level and hedgehog spin texture in gapped graphene.

Varykhalov A, Sánchez-Barriga J, Marchenko D, Hlawenka P, Mandal PS, Rader O - Nat Commun (2015)

Effect of gating on the vectorial spin texture of graphene Fermi surface.Minor change of charge doping from (a) n-type to (b) p-type shifts Fermi level from the apex of upper gapped Dirac cone π* to the apex of lower cone π and switches the direction of out-of-plane spin while the in-plane spin texture remains unchanged. Red and green arrows sketch in-plane spins of Rashba split bands circulating in opposite directions. Black arrows denote hedgehog spins within the gap of the Dirac cone.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525204&req=5

f4: Effect of gating on the vectorial spin texture of graphene Fermi surface.Minor change of charge doping from (a) n-type to (b) p-type shifts Fermi level from the apex of upper gapped Dirac cone π* to the apex of lower cone π and switches the direction of out-of-plane spin while the in-plane spin texture remains unchanged. Red and green arrows sketch in-plane spins of Rashba split bands circulating in opposite directions. Black arrows denote hedgehog spins within the gap of the Dirac cone.
Mentions: The hedgehog spin texture becomes the key to spin functionality in the context of Fermi level tuning which is shown here by varying the Au concentration (Fig. 3a,b). Aligning the bandgap to the Fermi level also tunes the vectorial spin texture of the graphene Fermi surface at and valleys, as illustrated in Fig. 4. This, in turn, is highly relevant for the emerging field of valleytronics dealing with electronic devices based on valley-dependent Berry phase effects2830. In particular, spin-valley scattering in graphene with broken sublattice symmetry and non-equivalent magnetic moments of and valleys may be used for the creation of highly effective spin separators (see Supplementary Note 6 and Supplementary Figure 7).

Bottom Line: First, a giant Rashba effect (∼70 meV splitting) away from the Dirac point and, second, the breaking of the six-fold graphene symmetry at the interface.Surprisingly, the graphene Fermi level is systematically tuned by the Au concentration and can be moved into the bandgap.We conclude that the out-of-plane spin texture is not only of fundamental interest but can be tuned at the Fermi level as a model for electrical gating of spin in a spintronic device.

View Article: PubMed Central - PubMed

Affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II, Albert-Einstein-Straße 15, 12489 Berlin, Germany.

ABSTRACT
Spin and pseudospin in graphene are known to interact under enhanced spin-orbit interaction giving rise to an in-plane Rashba spin texture. Here we show that Au-intercalated graphene on Fe(110) displays a large (∼230 meV) bandgap with out-of-plane hedgehog-type spin reorientation around the gapped Dirac point. We identify two causes responsible. First, a giant Rashba effect (∼70 meV splitting) away from the Dirac point and, second, the breaking of the six-fold graphene symmetry at the interface. This is demonstrated by a strong one-dimensional anisotropy of the graphene dispersion imposed by the two-fold-symmetric (110) substrate. Surprisingly, the graphene Fermi level is systematically tuned by the Au concentration and can be moved into the bandgap. We conclude that the out-of-plane spin texture is not only of fundamental interest but can be tuned at the Fermi level as a model for electrical gating of spin in a spintronic device.

No MeSH data available.