408 research outputs found
Rashba and intrinsic spin-orbit interactions in biased bilayer graphene
We investigate the effect that the intrinsic spin-orbit and the inter- and
intra-layer Rashba interactions have on the energy spectrum of either an
unbiased or a biased graphene bilayer. We find that under certain conditions, a
Dirac cone is formed out of a parabolic band and that it is possible to create
a "Mexican hat"-like energy dispersion in an unbiased bilayer. In addition, in
the presence of only an intralayer Rashba interaction, the K (K') point splits
into four distinct ones, contrarily to the case in single-layer graphene, where
the splitting also takes place, but the low-energy dispersion at these points
remains identical.Comment: 10 pages, 10 figure
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Openbare les Vrije Universiteit Amsterda
Spin-density-wave instability in graphene doped near the van Hove singularity
We study the instability of the metallic state towards the formation of a new
ground state in graphene doped near the van Hove singularity. The system is
described by the Hubbard model and a field theoretical approach is used to
calculate the charge and spin susceptibility. We find that for repulsive
interactions, within the random phase approximation, there is a competition
between ferromagnetism and spin-density wave (SDW). It turns out that a SDW
with a triangular geometry is more favorable when the Hubbard parameter is
above the critical value U_c(T), which depends on the temperature T, even if
there are small variations in the doping. Our results can be verified by ARPES
or neutron scattering experiments in highly doped graphene.Comment: 5 pages, 5 figures, 1 tabl
Multiple vanishing tumours simulating pulmonary neoplasms. A case report
CITATION: Van Gelderen, W.F.C. 1989. Multiple vanishing tumours simulating pulmonary neoplasms. A case report. S Afr Med J, 75:498-499.The original publication is available at http://www.samj.org.zaVanishing fluid collection (or tumour) in an interlobar fissure associated with congestive cardiac failure is not common. Multiple vanishing tumours are most uncommon and can resemble other multiple opacities, e.g. metastases. The disappearance of these so-called tumours after treatment for cardiac failure provided proof of the diagnosis in the patient reported. This diagnosis is important to consider in order to prevent unnecessary investigation and treatment.Publisher’s versio
Spin- and band-ferromagnetism in trilayer graphene
We study the ground state properties of an ABA-stacked trilayer graphene. The
low energy band structure can be described by a combination of both a linear
and a quadratic particle-hole symmetric dispersions, reminiscent of monolayer-
and bilayer-graphene, respectively. The multi-band structure offers more
channels for instability towards ferromagnetism when the Coulomb interaction is
taken into account. Indeed, if one associates a pseudo-spin 1/2 degree of
freedom to the bands (parabolic/linear), it is possible to realize also a
band-ferromagnetic state, where there is a shift in the energy bands, since
they fill up differently. By using a variational procedure, we compute the
exchange energies for all possible variational ground states and identify the
parameter space for the occurrence of spin- and band-ferromagnetic
instabilities as a function of doping and interaction strength.Comment: 9 pages/ 8 figure
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