2,932 research outputs found
Effect of electron-electron interactions on the conductivity of clean graphene
Minimal conductivity of a single undoped graphene layer is known to be of the
order of the conductance quantum, independent of the electron velocity. We show
that this universality does not survive electron-electron interaction which
results in the non-trivial frequency dependence. We begin with analyzing the
perturbation theory in the interaction parameter 'g' for the electron
self-energy and observe the failure of the random-phase approximation. The
optical conductivity is then derived from the quantum kinetic equation and the
exact result is obtained in the limit when g << 1 << g ln\omega.Comment: 4 pages, 3 figures; final versio
Coherent macroscopic quantum tunneling in boson-fermion mixtures
We show that the cold atom systems of simultaneously trapped Bose-Einstein
condensates (BEC's) and quantum degenerate fermionic atoms provide promising
laboratories for the study of macroscopic quantum tunneling. Our theoretical
studies reveal that the spatial extent of a small trapped BEC immersed in a
Fermi sea can tunnel and coherently oscillate between the values of the
separated and mixed configurations (the phases of the phase separation
transition of BEC-fermion systems). We evaluate the period, amplitude and
dissipation rate for Na and K-atoms and we discuss the
experimental prospects for observing this phenomenon.Comment: 4 pages, 3 figure
Dielectric function, screening, and plasmons in 2D graphene
The dynamical dielectric function of two dimensional graphene at arbitrary
wave vector and frequency , , is calculated in
the self-consistent field approximation. The results are used to find the
dispersion of the plasmon mode and the electrostatic screening of the Coulomb
interaction in 2D graphene layer within the random phase approximation. At long
wavelengths () the plasmon dispersion shows the local classical
behavior , but the density dependence of the
plasma frequency () is different from the usual 2D
electron system (). The wave vector dependent plasmon
dispersion and the static screening function show very different behavior than
the usual 2D case.Comment: 6 pages, 3 figure
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