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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.


Related in: MedlinePlus

Observation of tunable doping and hedgehog spin texture in Au-intercalated graphene/Fe(110).(a,b) Dirac cones in graphene/Fe(110) intercalated with (a) 1 ML and (b) 2 ML of Au display a bandgap Eg∼230 meV and different charge dopings. The effect is emphasized by intensity profiles (EDCs) sliced through the Dirac point. Increased concentration of Au makes graphene nearly charge neutral and moves the Fermi level into the gap. Red line in the Brillouin zone denotes the direction along which the dispersion was measured. (c–e) Spin-resolved photoemission of graphene intercalated with 1 ML of Au measured at positive k+ (c) and negative k− (d,e) wave vectors relative to . The panels display spin-resolved spectra together with the measured spin polarizations. Red and green colours and arrows in c and d denote opposite directions of spin circulation in the graphene plane. In e, the same colours denote out-of-plane spin components. For in-plane components the data in c,d reveals a giant spin–orbit splitting of the Dirac cone (ΔSO∼70 meV) which reverses its sign between k− and k+. However, the out-of-plane spin splitting is zero (e). This clearly indicates Rashba physics. (f) Spin-resolved measurements of graphene intercalated with 1 ML Au taken within the bandgap at the Dirac point (wave vector k0). Here red and green denote spin components of opposite sign which are perpendicular to the graphene plane. Data reveal out-of-plane spin polarization of gap edges and evidence the formation of a hedgehog spin configuration (g).
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f3: Observation of tunable doping and hedgehog spin texture in Au-intercalated graphene/Fe(110).(a,b) Dirac cones in graphene/Fe(110) intercalated with (a) 1 ML and (b) 2 ML of Au display a bandgap Eg∼230 meV and different charge dopings. The effect is emphasized by intensity profiles (EDCs) sliced through the Dirac point. Increased concentration of Au makes graphene nearly charge neutral and moves the Fermi level into the gap. Red line in the Brillouin zone denotes the direction along which the dispersion was measured. (c–e) Spin-resolved photoemission of graphene intercalated with 1 ML of Au measured at positive k+ (c) and negative k− (d,e) wave vectors relative to . The panels display spin-resolved spectra together with the measured spin polarizations. Red and green colours and arrows in c and d denote opposite directions of spin circulation in the graphene plane. In e, the same colours denote out-of-plane spin components. For in-plane components the data in c,d reveals a giant spin–orbit splitting of the Dirac cone (ΔSO∼70 meV) which reverses its sign between k− and k+. However, the out-of-plane spin splitting is zero (e). This clearly indicates Rashba physics. (f) Spin-resolved measurements of graphene intercalated with 1 ML Au taken within the bandgap at the Dirac point (wave vector k0). Here red and green denote spin components of opposite sign which are perpendicular to the graphene plane. Data reveal out-of-plane spin polarization of gap edges and evidence the formation of a hedgehog spin configuration (g).

Mentions: The Au also mediates a concentration-dependent charge doping, which is known for graphene/Au/SiC21 but has not been seen on metal substrates so far. While for 1 ML of intercalated Au the graphene is n-doped and the Dirac cone is shifted toward higher binding energies (ED=EF−210 meV; Fig. 3a), for intercalation of nominally 2 ML it is charge neutral (ED=EF; Fig. 3b). Here ED denotes the binding energy of Dirac point and EF is the Fermi level.


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)

Observation of tunable doping and hedgehog spin texture in Au-intercalated graphene/Fe(110).(a,b) Dirac cones in graphene/Fe(110) intercalated with (a) 1 ML and (b) 2 ML of Au display a bandgap Eg∼230 meV and different charge dopings. The effect is emphasized by intensity profiles (EDCs) sliced through the Dirac point. Increased concentration of Au makes graphene nearly charge neutral and moves the Fermi level into the gap. Red line in the Brillouin zone denotes the direction along which the dispersion was measured. (c–e) Spin-resolved photoemission of graphene intercalated with 1 ML of Au measured at positive k+ (c) and negative k− (d,e) wave vectors relative to . The panels display spin-resolved spectra together with the measured spin polarizations. Red and green colours and arrows in c and d denote opposite directions of spin circulation in the graphene plane. In e, the same colours denote out-of-plane spin components. For in-plane components the data in c,d reveals a giant spin–orbit splitting of the Dirac cone (ΔSO∼70 meV) which reverses its sign between k− and k+. However, the out-of-plane spin splitting is zero (e). This clearly indicates Rashba physics. (f) Spin-resolved measurements of graphene intercalated with 1 ML Au taken within the bandgap at the Dirac point (wave vector k0). Here red and green denote spin components of opposite sign which are perpendicular to the graphene plane. Data reveal out-of-plane spin polarization of gap edges and evidence the formation of a hedgehog spin configuration (g).
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getmorefigures.php?uid=PMC4525204&req=5

f3: Observation of tunable doping and hedgehog spin texture in Au-intercalated graphene/Fe(110).(a,b) Dirac cones in graphene/Fe(110) intercalated with (a) 1 ML and (b) 2 ML of Au display a bandgap Eg∼230 meV and different charge dopings. The effect is emphasized by intensity profiles (EDCs) sliced through the Dirac point. Increased concentration of Au makes graphene nearly charge neutral and moves the Fermi level into the gap. Red line in the Brillouin zone denotes the direction along which the dispersion was measured. (c–e) Spin-resolved photoemission of graphene intercalated with 1 ML of Au measured at positive k+ (c) and negative k− (d,e) wave vectors relative to . The panels display spin-resolved spectra together with the measured spin polarizations. Red and green colours and arrows in c and d denote opposite directions of spin circulation in the graphene plane. In e, the same colours denote out-of-plane spin components. For in-plane components the data in c,d reveals a giant spin–orbit splitting of the Dirac cone (ΔSO∼70 meV) which reverses its sign between k− and k+. However, the out-of-plane spin splitting is zero (e). This clearly indicates Rashba physics. (f) Spin-resolved measurements of graphene intercalated with 1 ML Au taken within the bandgap at the Dirac point (wave vector k0). Here red and green denote spin components of opposite sign which are perpendicular to the graphene plane. Data reveal out-of-plane spin polarization of gap edges and evidence the formation of a hedgehog spin configuration (g).
Mentions: The Au also mediates a concentration-dependent charge doping, which is known for graphene/Au/SiC21 but has not been seen on metal substrates so far. While for 1 ML of intercalated Au the graphene is n-doped and the Dirac cone is shifted toward higher binding energies (ED=EF−210 meV; Fig. 3a), for intercalation of nominally 2 ML it is charge neutral (ED=EF; Fig. 3b). Here ED denotes the binding energy of Dirac point and EF is the Fermi level.

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.


Related in: MedlinePlus