13,793 research outputs found
Conductivity of graphene in the framework of Dirac model: Interplay between nonzero mass gap and chemical potential
The complete theory of electrical conductivity of graphene at arbitrary
temperature is developed with taken into account mass-gap parameter and
chemical potential. Both the in-plane and out-of-plane conductivities of
graphene are expressed via the components of the polarization tensor in
(2+1)-dimensional space-time analytically continued to the real frequency axis.
Simple analytic expressions for both the real and imaginary parts of the
conductivity of graphene are obtained at zero and nonzero temperature. They
demonstrate an interesting interplay depending on the values of mass gap and
chemical potential. In the local limit, several results obtained earlier using
various approximate and phenomenological approaches are reproduced, refined and
generalized. The numerical computations of both the real and imaginary parts of
the conductivity of graphene are performed to illustrate the obtained results.
The analytic expressions for the conductivity of graphene obtained in this
paper can serve as a guide in the comparison between different theoretical
approaches and between experiment and theory.Comment: 27 pages, 5 figures; accepted for publication in Phys. Rev.
Nonlinearity of vacuum reggeons and exclusive diffractive production of vector mesons at HERA
The processes of exclusive photo- and electroproduction of vector mesons
(770), (1020) and (3096) at collision energies and transferred momenta squared are considered in
the framework of a phenomenological Regge-eikonal scheme with nonlinear Regge
trajectories in which their QCD asymptotic behavior is taken into account
explicitly. By comparison of available experimental data from ZEUS and H1
Collaborations with the model predictions it is demonstrated that corresponding
angular distributions and integrated cross-sections in the above-mentioned
kinematical range can be quantitatively described with use of two -even
vacuum Regge trajectories. These are the "soft" pomeron dominating the high
energy reactions without a hard scale and the "hard" pomeron giving an
essential contribution to photo- and electroproduction of heavy vector mesons
and deeply virtual electroproduction of light vector mesons.Comment: 25 pages, 12 figure
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