584 research outputs found
Instanton-induced Azimuthal Spin Asymmetry in Deep Inelastic Scattering
It is by now well understood that spin asymmetry in deep inelastic scattering
(DIS) can appear if two things are both present: (i) a chirality flip of the
struck quark; (ii) a nonzero T-odd phase due to its final state interaction. So
far (i) was attributed to a new structure/wave function of the nucleon and (ii)
to some gluon exchanges. We propose a new mechanism utilizing strong vacuum
fluctuations of the gluon field described semiclasically by instantons, and
show that both (i) and (ii) are present. The magnitude of the effect is
estimated using known parameters of the instanton ensemble in the QCD vacuum
and known structure and fragmentation functions, without any new free
parameters. The result agrees in sign and (roughly) in magnitude with the
available data on single particle inclusive DIS. Furthermore, our predictions
uniquely relate effects for longitudinally and transversely polarized targets.Comment: version 2 includes few refs and new fig.5 which contains comparison
to recent dat
Conductivity of disordered graphene at half filling
We study electron transport properties of a monoatomic graphite layer
(graphene) with different types of disorder at half filling. We show that the
transport properties of the system depend strongly on the symmetry of disorder.
We find that the localization is ineffective if the randomness preserves one of
the chiral symmetries of the clean Hamiltonian or does not mix valleys. We
obtain the exact value of minimal conductivity in the case of
chiral disorder. For long-range disorder (decoupled valleys), we derive the
effective field theory. In the case of smooth random potential, it is a
symplectic-class sigma model including a topological term with .
As a consequence, the system is at a quantum critical point with a universal
value of the conductivity of the order of . When the effective time
reversal symmetry is broken, the symmetry class becomes unitary, and the
conductivity acquires the value characteristic for the quantum Hall transition.Comment: 11 pages, 2 EPS figures; Proceedings of Graphene Conference, MPIPKS
Dresden 200
Metallic proximity effect in ballistic graphene with resonant scatterers
We study the effect of resonant scatterers on the local density of states in
a rectangular graphene setup with metallic leads. We find that the density of
states in a vicinity of the Dirac point acquires a strong position dependence
due to both metallic proximity effect and impurity scattering. This effect may
prevent uniform gating of weakly-doped samples. We also demonstrate that even a
single-atom impurity may essentially alter electronic states at low-doping on
distances of the order of the sample size from the impurity.Comment: 9 pages, 2 figure
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