1,076 research outputs found
Unconventional Integer Quantum Hall effect in graphene
Monolayer graphite films, or graphene, have quasiparticle excitations that
can be described by 2+1 dimensional Dirac theory. We demonstrate that this
produces an unconventional form of the quantized Hall conductivity with , that notably distinguishes graphene from
other materials where the integer quantum Hall effect was observed. This
unconventional quantization is caused by the quantum anomaly of the
Landau level and was discovered in recent experiments on ultrathin graphite
films.Comment: 4 pages, RevTeX4, 2 EPS figures; version accepted for publication in
Physical Review Letter
Phase fluctuations and Non-Fermi Liquid Properties of 2D Fermi-system with attraction
The effect of static fluctuations in the phase of the order parameter on the
normal and superconducting properties of a 2D system with attractive
four-fermion interaction has been studied. Analytic expressions for the fermion
Green function, its spectral density and the density of states are derived. The
resultant single-particle Green function clearly demonstrates non-Fermi liquid
behavior. The results show that as the temperature increases through the 2D
critical temperature the width of the quasiparticle peaks broadens
significantly. At the same time one retains the gap in quasiparticle spectrum.
The spectral density for the dynamical fluctuations can also be obtained.
Clearly the dynamical fluctuations fill the gap giving the observed pseudogap
behaviour.Comment: 4 pages, LaTeX; invited paper presented at New^3SC-2, Las Vegas, USA,
199
Pseudogap phase formation in the crossover from Bose-Einstein condensation to BCS superconductivity in low dimensional systems
A phase diagram for a 2D metal with variable carrier density has been studied
using the modulus-phase representation for the order parameter in a fully
microscopic treatment. This amounts to splitting the degrees of freedom into
neutral fermion and charged boson degrees of freedom. Although true long range
order is forbidden in two dimensions, long range order for the neutral fermions
is possible since this does not violate any continuous symmetry. The phase
fluctuations associated with the charged degrees of freedom destroy long range
order in the full system as expected. The presence of the neutral order
parameter gives rise to new features in the superconducting condensate
formation in low dimensional systems. The resulting phase diagram contains a
new phase which lies above the superconducting (here
Berezinskii-Kosterlitz-Thouless) phase and below the normal (Fermi-liquid)
phase. We identify this phase with the pseudogap phase observed in underdoped
high- superconducting compounds above their critical temperature. We
also find that the phase diagram persists even in the presence of weak
3-dimensionalisation.Comment: 4 pages, LaTeX; invited paper presented at New^3SC-1, Baton Rouge,
USA, 1998. To be published in Int.J.Mod.Phys.
Edge states on graphene ribbon in magnetic field: interplay between Dirac and ferromagnetic-like gaps
By combining analytic and numerical methods, edge states on a finite width
graphene ribbon in a magnetic field are studied in the framework of low-energy
effective theory that takes into account the possibility of quantum Hall
ferromagnetism (QHF) gaps and dynamically generated Dirac-like masses. The
analysis is done for graphene ribbons with both zigzag and armchair edges. The
characteristic features of the spectrum of the edge states in both these cases
are described. In particular, the conditions for the existence of the gapless
edge states are established. Implications of these results for the
interpretation of recent experiments are discussed.Comment: 13 pages, 7 figures. v2: analysis for ribbons with armchair edges
added, to appear in Phys. Rev.
On the universal AC optical background in graphene
The latest experiments have confirmed the theoretically expected universal
value of the ac conductivity of graphene and have revealed
departures of the quasiparticle dynamics from predictions for the Dirac
fermions in idealized graphene. We present analytical expressions for the ac
conductivity in graphene which allow one to study how it is affected by
interactions, temperature, external magnetic field and the opening of a gap in
the quasiparticle spectrum. We show that the ac conductivity of graphene does
not necessarily give a metrologically accurate value of the von Klitzing
constant , because it is depleted by the electron-phonon interaction. In
a weak magnetic field the ac conductivity oscillates around the universal value
and the Drude peak evolves into a peak at the cyclotron frequency.Comment: 18 pages, 4 figures; v2: to match New J. Phys. (Focus on Graphene
issue
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