443 research outputs found
Negative differential conductance and magnetoresistance oscillations due to spin accumulation in ferromagnetic double-island devices
Spin-dependent electronic transport in magnetic double-island devices is
considered theoretically in the sequential tunneling regime. Electric current
and tunnel magnetoresistance are analyzed as a function of the bias voltage and
spin relaxation time in the islands. It is shown that the interplay of spin
accumulation on the islands and charging effects leads to periodic modification
of the differential conductance and tunnel magnetoresistance. For a
sufficiently long spin relaxation time, the modulations are associated with
periodic oscillations of the sign of both the tunnel magnetoresistance and
differential conductance
A re-analysis of the spectrum of 2206-199
Recently Pettini, Hunstead, Smith and Mar, (PHSM 1991) performed an analysis of the Ly-alpha forest of QSO 2206-199N at very high resolution. On the basis of their observations they concluded that most Doppler parameters b = (square root of 2)(sigma) of Ly-alpha forest lines are below 22 km/s, with a range down to a few km/s and a median of 17 km/s. They also found a strong intrinsic correlation between Doppler parameter b and column density N. These results are in contrast to those of a similar study by Carswell, Lanzetta, Parnell, and Webb (CLPW 1991) at comparable resolution with the same instruments, who find that most of the Ly-alpha lines towards QSO 1100-264 have Doppler parameters above 15 km/s (median b = 34 km/s), and that there is no significant correlation between b and N. Whilst an intrinsic difference between the lines of sight to 2206-199 and to other QSO's can not be excluded a priori, previous disagreement between Doppler parameter estimates obtained by both groups pointed to a potential difference in estimation techniques and in the interpretation of the results. To investigate this possibility, the AAT/UCLES spectrum of 2206-199 obtained by PHSM were reanalyzed. The spectrum was extracted from the raw data and determined the line parameters using the method described by CLPW
Deep H-band Galaxy Counts and Half-light Radii from HST/NICMOS Parallel Observations
We present deep galaxy counts and half-light radii from F160W
() images obtained with NICMOS on HST. Nearly 9 arcmin
have been imaged with camera 3, with depths ranging from H = 24.3 to
25.5 in a 0.6 diameter aperture. The slope of the counts fainter than H~ is 0.31, and the integrated surface density to H is galaxies per square degree. The half-light radii of the galaxies declines
steeply with apparent magnitude. At H~ we are limited by both the
delivered FWHM and the detection threshold of the images.Comment: 8 pages. Accepted for publication in ApJ Letter
Universality of the Kondo effect in quantum dots with ferromagnetic leads
We investigate quantum dots in clean single-wall carbon nanotubes with
ferromagnetic PdNi-leads in the Kondo regime. In most odd Coulomb valleys the
Kondo resonance exhibits a pronounced splitting, which depends on the tunnel
coupling to the leads and an external magnetic field , and only weakly on
gate voltage. Using numerical renormalization group calculations, we
demonstrate that all salient features of the data can be understood using a
simple model for the magnetic properties of the leads. The magnetoconductance
at zero bias and low temperature depends in a universal way on , where is the Kondo temperature and the external field
compensating the splitting.Comment: 4 pages, 4 figure
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