822 research outputs found
Multiple crossovers in interacting quantum wires
We study tunneling of electrons into and between interacting wires in the
spin-incoherent regime subject to a magnetic field. The tunneling currents
follow power laws of the applied voltage with exponents that depend on whether
the electron spins at the relevant length scales are polarized or disordered.
The crossover length (or energy) scale is exponential in the applied field. In
a finite size wire multiple crossovers can occur.Comment: 7 pages, 2 figure
Scaling and interaction-assisted transport in graphene with one-dimensional defects
We analyze the scattering from one-dimensional defects in intrinsic graphene.
The Coulomb repulsion between electrons is found to be able to induce
singularities of such scattering at zero temperature as in one-dimensional
conductors. In striking contrast to electrons in one space dimension, however,
repulsive interactions here can enhance transport. We present explicit
calculations for the scattering from vector potentials that appear when strips
of the material are under strain. There the predicted effects are exponentially
large for strong scatterers.Comment: 4 pages, 2 figure
Local sublattice-symmetry breaking in rotationally faulted multilayer graphene
Interlayer coupling in rotationally faulted graphene multilayers breaks the
local sublattice-symmetry of the individual layers. We present a theory of this
mechanism, which reduces to an effective Dirac model with space-dependent mass
in an important limit. It thus makes a wealth of existing knowledge available
for the study of rotationally faulted graphene multilayers. We demonstrate
quantitative agreement between our theory and a recent experiment.Comment: Valley dependence in Eqs. (2) and (7) corrected; coordinates x and y
interchanged in the appendi
Shot noise free conductance reduction in quantum wires
We show that a shot noise free current at conductance below 2 e^2/h is
possible in short interacting quantum wires without spin-polarization. Our
calculation is done for two exactly solvable limits of the ``Coulomb Tonks
gas'', a one-dimensional gas of impenetrable electrons that can be realized in
ultra-thin quantum wires. In both cases we find that charge transport through
such a wire is noiseless at zero temperature while the conductance is reduced
to e^2/h.Comment: 4 pages, 1 figur
The variable power coupler for the LHC superconducting cavity
Variable input couplers, providing a remotely controlled change of external Q by an order of magnitude under power, are required for the 400 MHz LHC superconducting cavities. These couplers must handle a forward power of 120 kW average and 180 kW pulsed with a large variety of load conditions up to full reflection. A summary of the LHC prototype coupler design (using d.c. bias on the main coupler transmission line to suppress multipactor) and of the RF power tests on a normal conducting test cavity will be given. The same couplers now have been RF power tested on a prototype superconducting LHC bi-module. During both of these RF tests, multipactor events have also been observed in the variable coupler part - outside the main coupler line - which cannot be suppressed by the actual d.c. bias. An improved design with a second d.c. bias will therefore be implemented. Nevertheless, after the usual RF conditioning, these prototype couplers have successfully passed all RF tests at power levels well above the LHC requirements
RF Power Tests of LEP2 Main couplers on a Single Cell Superconducting Cavity
To determine the power capability of the input couplers for the LEP2 superconducting (SC) cavities a new test set-up has been built. The new set-up permits tests at high RF power levels under realistic conditions (cooled-down SC cavity). The couplers have been exposed to high RF power in matched and unmatched CW conditions as well as in pulsed operation. Power levels of more than 500 kW CW have been reached
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