APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011;
Dallas, Texas
Abstract: X16.00004 : Spin-orbit coupling in graphene: from single layers to graphite
3:06 PM–3:42 PM
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The spin-orbit interaction in graphene is full of contrasts.
First, this relativistic interaction destroys the ideal
relativistic ``touching cones'' electronic dispersion at the K
points. A finite, albeit small, gap appears, giving a finite mass
to the electrons. Then, while the spin-orbit splitting
in the carbon atom is about 10 meV, the electronic states at the
K points have a gap of only about 24 micro eV. Finally, it turns
out that this quintessential sp material has its spin-orbit
coupling derived almost exclusively from d orbitals. In this talk
I will give first-principles [1] and tight-binding [2]
perspectives on the spin-orbit coupling in graphene in
the presence of a transverse electric field. The field, which
would normally come from the substrate or the gates, breaks the
space inversion symmetry and gives the extrinsic (Bychkov-Rashba)
splitting of the states. It also brings interesting
band-structure topologies, from gapped at low electric
fields (the topological insulator phase), through a mixture of
genuine touching Dirac cones and parabolic bands (the intrinsic
and extrinsic spin-orbit strengths equal), to gapples, dominated
by the extrinsic effects [1]. The intrinsic coupling is dominated
by d orbitals, while the extrinsic by the field induced
hybridization of the s and p orbitals. It turns out
that similar physics holds for bilayer and trilayer graphene,
ultimately also in graphite. I will also discuss the problem of
the spin relaxation in graphene. The main issue is that
conventional theories predict microseconds for the spin
relaxation time, while experiments seem to consistently yield
100 ps. One possibility [3] is that that spin relaxation in
graphene is due to adatoms that pull out the carbon-like
spin-orbit coupling of the p electrons and lead to the larger
spin relaxation of the Dyakonov-Perel type.\\[4pt]
[1] M. Gmitra et al., Phys. Rev. B 80, 235431 (2009);\\[0pt]
[2] S. Konschuh et al., Phys. Rev. B (in press);\\[0pt]
[3] C. Ertler et al., Phys. Rev. B(R) 80, 041405 (2009).
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2011.MAR.X16.4