5,381 research outputs found
Possible Verification of Tilted Anisotropic Dirac Cone in \alpha-(BEDT-TTF)_2 I_3 Using Interlayer Magnetoresistance
It is proposed that the presence of a tilted and anisotropic Dirac cone can
be verified using the interlayer magnetoresistance in the layered Dirac fermion
system, which is realized in quasi-two-dimensional organic compound
\alpha-(BEDT-TTF)_2 I_3. Theoretical formula is derived using the analytic
Landau level wave functions and assuming local tunneling of electrons. It is
shown that the resistivity takes the maximum in the direction of the tilt if
anisotropy of the Fermi velocity of the Dirac cone is small. The procedure is
described to determine the parameters of the tilt and anisotropy.Comment: 4 pages, 4 figures, corrected Fig.
Calibration System with Cryogenically-Cooled Loads for CMB Polarization Detectors
We present a novel system to calibrate millimeter-wave polarimeters for CMB
polarization measurements. This technique is an extension of the conventional
metal mirror rotation approach, however it employs cryogenically-cooled
blackbody absorbers. The primary advantage of this system is that it can
generate a slightly polarized signal ( mK) in the laboratory; this is
at a similar level to that measured by ground-based CMB polarization
experiments observing a 10 K sky. It is important to reproduce the
observing condition in the laboratry for reliable characterization of
polarimeters before deployment. In this paper, we present the design and
principle of the system, and demonstrate its use with a coherent-type
polarimeter used for an actual CMB polarization experiment. This technique can
also be applied to incoherent-type polarimeters and it is very promising for
the next-generation CMB polarization experiments.Comment: 7 pages, 9 figures Submitted to RS
Innovative Demodulation Scheme for Coherent Detectors in CMB Experiments
We propose an innovative demodulation scheme for coherent detectors used in
cosmic microwave background polarization experiments. Removal of non-white
noise, e.g., narrow-band noise, in detectors is one of the key requirements for
the experiments. A combination of modulation and demodulation is used to
extract polarization signals as well as to suppress such noise. Traditional
demodulation, which is based on the two- point numerical differentiation, works
as a first-order high pass filter for the noise. The proposed demodulation is
based on the three-point numerical differentiation. It works as a second-order
high pass filter. By using a real detector, we confirmed significant
improvements of suppression power for the narrow-band noise. We also found
improvement of the noise floor.Comment: 3 pages, 4 figure
Sub-TeV proton beam generation by ultra-intense laser irradiation of foil-and-gas target
A two-phase proton acceleration scheme using an ultra-intense laser pulse irradiating a proton foil with a tenuous heavier-ion plasma behind it is presented. The foil electrons are compressed and pushed out as a thin dense layer by the radiation pressure and propagate in the plasma behind at near the light speed. The protons are in turn accelerated by the resulting space-charge field and also enter the backside plasma, but without the formation of a quasistationary double layer. The electron layer is rapidly weakened by the space-charge field. However, the laser pulse originally behind it now snowplows the backside-plasma electrons and creates an intense electrostatic wakefield. The latter can stably trap and accelerate the pre-accelerated proton layer there for a very long distance and thus to very high energies. The two-phase scheme is verified by particle-in-cell simulations and analytical modeling, which also suggests that a 0.54 TeV proton beam can be obtained with a 10(23) W/cm(2) laser pulse. (C) 2012 American Institute of Physics. [doi:10.1063/1.3684658]Physics, Fluids & PlasmasSCI(E)EI0ARTICLE2null1
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