2,640 research outputs found
Dynamics of the particle - hole pair creation in graphene
The process of coherent creation of particle - hole excitations by an
electric field in graphene is quantitatively described. We calculate the
evolution of current density, number of pairs and energy after switching on the
electric field. In particular, it leads to a dynamical visualization of the
universal finite resistivity without dissipation in pure graphene. We show that
the DC conductivity of pure graphene is rather than the
often cited value of . This value coincides with the AC
conductivity calculated and measured recently at optical frequencies. The
effect of temperature and random chemical potential (charge puddles) are
considered and explain the recent experiment on suspended graphene. A
possibility of Bloch oscillations is discussed within the tight binding model.Comment: 4 pages, 2 figure
Tetanic Stimulation Leads to Increased Accumulation of Ca^(2+)/Calmodulin-Dependent Protein Kinase II via Dendritic Protein Synthesis in Hippocampal Neurons
mRNA for the ɑ-subunit of CaMKII is abundant in dendrites of neurons in the forebrain (Steward, 1997). Here we show that tetanic stimulation of the Schaffer collateral pathway causes an increase in the concentration of ɑ-CaMKII in the dendrites of postsynaptic neurons. The increase is blocked by anisomycin and is detected by both quantitative immunoblot and semiquantitative immunocytochemistry. The increase in dendritic ɑ-CaMKII can be measured 100-200 µm away from the neuronal cell bodies as early as 5 min after a tetanus. Transport mechanisms for macromolecules from neuronal cell bodies are not fast enough to account for this rapid increase in distal portions of the dendrites. Therefore, we conclude that dendritic protein synthesis must produce a portion of the newly accumulated CaMKII. The increase in concentration of dendritic CaMKII after tetanus, together with the previously demonstrated increase in autophosphorylated CaMKII (Ouyang et al., 1997), will produce a prolonged increase in steady-state kinase activity in the dendrites, potentially influencing mechanisms of synaptic plasticity that are controlled through phosphorylation by CaMKII
Signature of Schwinger's pair creation rate via radiation generated in graphene by strong electric current
Electron - hole pairs are copuously created by an applied electric field near
the Dirac point in graphene or similar 2D electronic systems. It was shown
recently that for sufficiently large electric fields and ballistic times the
I-V characteristics become strongly nonlinear due to Schwinger's pair creation.
Since there is no energy gap the radiation from the pairs' annihilation is
enhanced. The spectrum of radiation is calculated. The angular and polarization
dependence of the emitted photons with respect to the graphene sheet is quite
distinctive. For very large currents the recombination rate becomes so large
that it leads to the second Ohmic regime due to radiation friction.Comment: 9 pages, 7 figure
Dynamics of the chiral phase transition in the 2+1 dimensional Gross-Neveu model
The phase diagram of the Gross-Neveu (G-N) model in 2+1 dimensions as a
function of chemical potential and temperature has a simple curve separating
the broken symmetry and unbroken symmetry phases, with chiral symmetry being
restored both at high temperature and high density. We study, in leading order
in the 1/N expansion, the dynamics of the chiral phase transition for an
expanding plasma of quarks in the Gross-Neveu model in 2+1 dimensions assuming
boost invariant kinematics. We compare the time evolution of the order
parameter (mass of the fermion) for evolutions starting in the unbroken and
broken phases. The proper time evolution of the order parameter resembles
previous results in the 1+1 dimensional G-N model in the same approximation.
The time needed to traverse the transition is insensitive to mu.Comment: 10 pages, 3 figure
The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors
We explain 90 degree reorientation in the vortex lattice of borocarbide
superconductors on the basis of a phenomenological extension of the nonlocal
London model that takes full account of the symmetry of the system. We propose
microscopic mechanisms that could generate the correction terms and point out
the important role of the superconducting gap anisotropy.Comment: 4 pages, 2 eps figure
Ballistic transport, chiral anomaly and emergence of the neutral electron - hole plasma in graphene
The process of coherent creation of particle - hole excitations by an
electric field in graphene is quantitatively described using a dynamic "first
quantized" approach. We calculate the evolution of current density, number of
pairs and energy in ballistic regime using the tight binding model. The series
in electric field strength up to third order in both DC and AC are
calculated. We show how the physics far from the two Dirac points enters
various physical quantities in linear response and how it is related to the
chiral anomaly. The third harmonic generation and the imaginary part of
conductivity are obtained. It is shown that at certain time scale
the physical behaviour dramatically changes and the
perturbation theory breaks down. Beyond the linear response physics is explored
using an exact solution of the first quantized equations. While for small
electric fields the I-V curve is linear characterized by the universal minimal
resistivity %, at the conductivity grows
fast. The copious pair creation (with rate ), analogous to Schwinger's
electron - positron pair creation from vacuum in QED, leads to creation of the
electron - hole plasma at ballistic times of order . This process is
terminated by a relaxational recombination.Comment: 15 pages, 5 figures
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