44,180 research outputs found
Dynamical chiral symmetry breaking in QED at finite density and impurity potential
We study the effects of finite chemical potential and impurity scattering on
dynamical fermion mass generation in (2+1)-dimensional quantum electrodynamics.
In any realistic systems, these effects usually can not be neglected. The
longitudinal component of gauge field develops a finite static length produced
by chemical potential and impurity scattering, while the transverse component
remains long-ranged because of the gauge invariance. Another important
consequence of impurity scattering is that the fermions have a finite damping
rate, which reduces their lifetime staying in a definite quantum state. By
solving the Dyson-Schwinger equation for fermion mass function, it is found
that these effects lead to strong suppression of the critical fermion flavor
and the dynamical fermion mass in the symmetry broken phase.Comment: 8 pages, 4 figure
Diffusive versus displacive contact plasticity of nanoscale asperities: Temperature- and velocity-dependent strongest size
We predict a strongest size for the contact strength when asperity radii of
curvature decrease below ten nanometers. The reason for such strongest size is
found to be correlated with the competition between the dislocation plasticity
and surface diffusional plasticity. The essential role of temperature is
calculated and illustrated in a comprehensive asperity size-strengthtemperature
map taking into account the effect of contact velocity. Such a map should be
essential for various phenomena related to nanoscale contacts such as nanowire
cold welding, self-assembly of nanoparticles and adhesive nano-pillar arrays,
as well as the electrical, thermal and mechanical properties of macroscopic
interfaces
Interaction and excitonic insulating transition in graphene
The strong long-range Coulomb interaction between massless Dirac fermions in
graphene can drive a semimetal-insulator transition. We show that this
transition is strongly suppressed when the Coulomb interaction is screened by
such effects as disorder, thermal fluctuation, doping, and finite volume. It is
completely suppressed once the screening factor is beyond a threshold
even for infinitely strong coupling. However, such transition is
still possible if there is an additional strong contact four-fermion
interaction. The differences between screened and contact interactions are also
discussed.Comment: 7 pages, 4 figures, to appear in Phys. Rev.
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